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Quadriceps muscle activity in female runners with patellofemoral pain syndrome 1986

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QUADRICEPS MUSCLE ACTIVITY IN FEMALE RUNNERS WITH PATELLOFEMORAL PAIN SYNDROME by DONNA LEE MACINTYRE B.S.R., The University of British Columbia, 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE DEGREE OF MASTER OF PHYSICAL EDUCATION in THE FACULTY OF GRADUATE STUDIES School of Physical Education and Recreation He accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July 1986 ® Donna Lee Maclntyre, 1986 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of pHi^icAu £DnCA)'0O The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date (Dot E-6 (3/81) ABSTRACT The a im o f t h i s s t u d y was t o d e t e r m i n e i f t h e r e was a d i f f e r e n c e i n t h e s u r f a c e EMG p a t t e r n s o f t h r e e o f t h e q u a d r i c e p s m u s c l e s ( v a s t u s med i a l i s , v a s t u s l a t e r a l i s and r e c t u s f e m o r i s ) i n f e m a l e r u n n e r s d i a g n o s e d w i t h p a t e l l o f e m o r a l p a i n syndrome (PFPS) compared t o t h e q u a d r i c e p s a c t i v i t y o f f e m a l e r u n n e r s f r e e o f knee p a i n and w i t h norma l l o w e r e x t r e m i t y a l i g n m e n t . L i n e a r e n v e l o p e EMGs f r om v a s t u s m e d i a l i s , v a s t u s l a t e r a l i s and r e c t u s f e m o r i s , t o g e t h e r w i t h a f o o t s w i t c h s i g n a l , were d i g i t a l l y r e c o r d e d as each s u b j e c t r an on a t r e a d m i l l a t 12 km/h . Each s t r i d e p e r i o d was n o r m a l i z e d t o 100%, and t hen t h e l i n e a r e n v e l o p e s f o r t e n t r i a l s f r om each mus c l e were ensemb le a v e r aged t o a c h i e v e a mean ensemb le f o r each mus c l e f r om each s u b j e c t . S u b s e q u e n t l y , t h e g r and mean ensemb le o f each mus c l e f o r a l l o f t h e s u b j e c t s i n each g roup was computed . I t was a l s o t h e o b j e c t i v e o f t h i s s t u d y t o d e t e r m i n e i f t h e r e was a d i f f e r e n c e i n t h e peak c o n c e n t r i c and e c c e n t r i c t o r q u e s o f t h e q u a d r i c e p s and t h e h a m s t r i n g s between t h e e x p e r i m e n t a l g roup and t h e c o n t r o l g r o u p . The s u b j e c t s were t e s t e d on an i s o k i n e t i c dynamometer (KINCOM) t h r o u g h a range o f 90° a t an a n g u l a r v e l o c i t y o f 200°/s. The r e s u l t s showed no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s between t h e g roups f o r t h e peak EMG a m p l i t u d e s . In f a c t when c ompa r i n g t h e EMG p a t t e r n s o f a c t i v i t y between t h e two g r o u p s , t h e g r and ensemb le a ve r age o f i n the experimental group remained within + one standard deviation of the control group's mean EMG pattern. However, when individual subjects with PFPS were compared to the control group, there were periods 1n the gait cycle when the EMG amplitude was outside of + one standard deviation of the control group's mean. When comparing the two groups for the peak concentric and eccentric torques of each muscle group, again the results were not s t a t i s t i c a l l y significant. The peak torques were also compared between groups as hamstrings/quadriceps ratios but found to be not significantly different. However, the mean concentric hamstrings/quadriceps ratio of the group with PFPS was found to be 1.02, which is outside of the range of values reported 1n the literature. TABLE OF CONTENTS A b s t r a c t i i L i s t o f T a b l e s v i L i s t o f F i g u r e s v i i Acknowl edgements v i i i I n t r o d u c t i o n 1 Pu r po s e 3 Me thodo l ogy 4 S u b j e c t s 4 E x p e r i m e n t a l P r o c e d u r e 5 T e s t i n g o f M u s c l e S t r e n g t h 5 EMG Measurement 7 S t a t i s t i c a l A n a l y s i s 8 R e s u l t s 10 D i s c u s s i o n 21 Group Mean M u s c l e A c t i v a t i o n P a t t e r n s 21 Peak C o n c e n t r i c and E c c e n t r i c To rque V a l u e s 24 C o n c l u s i o n s 31 Recommendat ions 33 V R e f e r e n c e s 34 Append i x 1 C h a r a c t e r i s t i c s o f t h e C o n t r o l Group S u b j e c t s and T h e i r I n d i v i d u a l Ensemb le A v e r a g e s 39 Append i x 2 I n d i v i d u a l Peak To rque V a l u e s and H a m s t r i n g s / Q u a d r i c e p s R a t i o s 53 Append i x 3 I n d i v i d u a l M u s c l e A c t i v a t i o n P a t t e r n s 55 Append i x 4 Rev iew o f t h e L i t e r a t u r e 81 P a t e l l o f e m o r a l P a i n Syndrome 82 I n t r o d u c t i o n 82 Anatomy o f t h e P a t e l l o f e m o r a l J o i n t 82 B i o m e c h a n i c s o f t h e P a t e l l o f e m o r a l J o i n t 85 C l i n i c a l F e a t u r e s 86 E t i o l o g y o f P a t e l l o f e m o r a l P a i n 90 E l e c t r o m y o g r a p h y 95 B i o m e c h a n i c a l S t u d i e s o f Runn i ng 98 I s o k i n e t i c Dynamometry 101 B i b l i o g r a p h y v i LIST OF TABLES I . D e s c r i p t i v e C h a r a c t e r i s t i c s o f t h e S u b j e c t s 10 I I . Summary o f Manova 14 EMG Peak A m p l i t u d e f o r V a s t u s M e d i a l i s , V a s t u s L a t e r a l i s and R e c t u s F e m o r i s I I I . Summary o f T - T e s t 15 IV . Mean Peak To rque V a l u e s a t 200°/s 16 f o r t h e R i g h t Q u a d r i c e p s and H a m s t r i n g s V . Summary o f Manova 17 Peak To rque V a l u e s - Group by M u s c l e by C o n t r a c t i o n V I . Summary o f T - T e s t 18 Peak To rque - A n a l y s i s by R a t i o s V I I . D e v i a t i o n s o f t h e EMG A m p l i t u d e s Compared t o t h e 20 C o n t r o l G r o u p ' s G rand Ensemb le Ave r age V I I I . C l i n i c a l C h a r a c t e r i s t i c s o f t h e C o n t r o l Group S u b j e c t s 39 I X . I n d i v i d u a l Peak To rque V a l u e s f o r t h e R i g h t Leg a t 200°/s. .53 X . I n d i v i d u a l C o n c e n t r i c and E c c e n t r i c H a m s t r i n g s / 54 Q u a d r i c e p s R a t i o s f o r t h e R i g h t Leg X I . C l i n i c a l C h a r a c t e r i s t i c s and Dynamic S t r e n g t h o f 55 Those S u b j e c t s W i t h R i g h t P a t e l l o f e m o r a l P a i n Syndrome v i i LIST OF FIGURES 1. Grand Ensemb le Ave r age s o f t h e C o n t r o l Group 11 2 . Grand Ensemble A v e r a g e s o f t h e E x p e r i m e n t a l Group 12 3 . G rand Ensemble Ave r age s o f t h e E x p e r i m e n t a l Group 13 Compared t o t h e C o n t r o l Group 4 . S u b j e c t CR 41 5 . S u b j e c t CS 42 6 . S u b j e c t GG 43 7 . S u b j e c t J F 44 8 . S u b j e c t LS 45 9 . S u b j e c t MR 46 1 0 . S u b j e c t PB 47 1 1 . S u b j e c t PW 48 1 2 . S u b j e c t SL 49 1 3 . S u b j e c t SO 50 1 4 . S u b j e c t SP 51 1 5 . S u b j e c t VA 52 1 6 . S u b j e c t SC 58 1 7 . S u b j e c t HB 61 1 8 . S u b j e c t EC 64 1 9 . S u b j e c t TR 67 2 0 . S u b j e c t RW 69 2 1 . S u b j e c t SS 71 2 2 . S u b j e c t JH 75 2 3 . S u b j e c t JG 77 v i i i ACKNOWLEDGEMENTS I wou l d l i k e t o e x p r e s s my a p p r e c i a t i o n t o D r . D. Gordon E. R o b e r t s o n f o r h i s g u i d a n c e , p a t i e n c e and encou ragement t h r o u g h o u t t h e c o u r s e o f my t h e s i s w o r k . I am a l s o g r a t e f u l t o D r . ' s Don M c K e n z i e , J a c k Taun ton and J e a n Wesse l f o r t h e i r s u p p o r t and a s s i s t a n c e w i t h o u t w h i c h I wou l d n o t have been a b l e t o c o m p l e t e t h i s s t u d y . F i n a l l y , I w i s h t o thank my f a m i l y and f r i e n d s who i n d i r e c t l y and o f t e n u n k n o w i n g l y have p r o v i d e d me w i t h u n d e r s t a n d i n g and t h e i n c e n t i v e t o c o m p l e t e what somet imes seemed l i k e an i m p o s s i b l e t a s k ! - 1 - INTRODUCTION The d r a m a t i c i n c r e a s e i n t h e p o p u l a r i t y o f e x e r c i s e , and i n p a r t i c u l a r r u n n i n g , i n t h e p a s t few decades has p r odu ced a need t o u n d e r s t a n d t h e b i o m e c h a n i c s o f r u n n i n g so t h a t e l i t e a t h l e t e s can improve t h e i r p e r f o r m - ances and c l i n i c i a n s can t r e a t and pe rhaps p r e v e n t r u n n i n g i n j u r i e s . T h i s need i s c o m p l i c a t e d by t h e f a c t t h a t t h e r e may be more v a r i a b i l i t y i n t h e mechan i c s o f r u n n i n g t h a n i n w a l k i n g . Mann (1982) s u g g e s t s t h a t speed i s one o b v i o u s v a r i a b l e w h i c h a f f e c t s r ange o f m o t i o n , m u s c l e a c t i v i t y and j o i n t f o r c e s i n t h e l o w e r e x t r e m i t y . However , i f t h e r u n n i n g speed c an be h e l d c o n s t a n t by a t r e a d m i l l , t h en a f a c t o r such as p h a s i c mus c l e a c t i v i t y can be s t u d i e d and compared between g r oups o f s u b j e c t s . Our s o c i e t y ' s i n c r e a s e d p a r t i c p a t i o n i n p h y s i c a l a c t i v i t y has a l s o r e s u l t e d i n an a s s o c i a t e d r i s e i n o v e r u s e i n j u r i e s . Ma lek and Mang ine (1981) and C l emen t e t a l . (1981) have f ound f r om t h e i r r e v i e w o f c l i n i c a l r e c o r d s t h a t t h e most common s i t e o f i n j u r y i s t h e knee and t h e most common c l i n i c a l f i n d i n g i s p a t e l l o f e m o r a l p a i n syndrome ( P F P S ) . P a t e l l o f e m o r a l p a i n syndrome has been d e s c r i b e d as a d i f f u s e , p o o r l y l o c a t e d p a i n a r ound t h e p a t e l l a w h i c h a r i s e s f r om abnormal t r a c k i n g o f t h e p a t e l l a (G rana e t a l . 1 9 8 4 ) . A n a t o m i c a l f a c t o r s w h i c h have been i d e n t i f i e d as h a v i n g some i n f l u e n c e on t h e a l i g n m e n t o f t h e p a t e l l a a r e genu v a l g um , genu r e c u r v a t u m , p a t e l l a a l t a , a h y p e r m o b i l e p a t e l l a , f emo r a l neck a n t e v e r s i o n , p r o n a t e d f e e t , i n e f f i c i e n c y o f t h e v a s t u s m e d i a l i s mus c l e a n d / o r h y p e r t r o p h y o f t h e v a s t u s l a t e r a l i s ( R e y n o l d s e t a l . 1 9 8 3 ) . - 2 - The e l e c t r o m y o g r a p h i c a c t i v i t y o f t h e m u s c l e s of t h e k n e e , i n p a r t i c u l a r t h e q u a d r i c e p s have been s t u d i e d i n i s o m e t r i c c o n t r a c t i o n s ( H a l l e n and L i n d a h l , 1967; L i e b and P e r r y , 1 9 7 1 ) , i n a c t i v e and r e s i s t e d mus c l e work ( P o c o c k , 1963; E l o r a n t a and K o m i , 1 9 8 1 ) , d u r i n g e c c e n t r i c and c o n c e n t r i c work ( K o m i , 1 9 7 3 ) , and d u r i n g t h e l a s t 30° o f e x t e n s i o n w h i l e w e i g h t - b e a r i n g ( R e y n o l d s e t a l , 1 9 8 3 ) . The n e x t l o g i c a l p r o g e s s i o n of musc l e a n a l y s i s p a r t i c u l a r t o r u n n i n g has been t o a n a l y z e t h e mus c l e a c t i v i t y d u r i n g a c t u a l r u n n i n g u s i n g EMG ( E l l i o t t and B l a n k s b y , 1979; Schwab e t a l . 1983; M a c l n t y r e and R o b e r t s o n , i n p r e s s ) . Improvements i n e l e c t r i c a l t e c h n o l o g y i n t h e p a s t few decades have made p o s s i b l e advancements i n e l e c t r o m y o g r a p h i c a n a l y s i s of g a i t . Th rough EMG s t u d i e s o f w a l k i n g , a b a s e l i n e of normal moto r p a t t e r n s has been e s t a b l i s h e d and s p e c i f i c a b n o r m a l i t i e s can be d e t e c t e d when compared t o t h e norm ( W i n t e r , 1 9 8 4 ) . U t i l i z i n g t h e s e same t e c h n i q u e s , i t i s a l s o p o s s i b l e t o s t u d y t h e p a t t e r n s of m u s c l e a c t i v i t y i n r u n n i n g and t o d e t e r m i n e i f t h e r e a r e o b s e r v a b l e a b n o r m a l i t i e s i n c e r t a i n c l i n i c a l c o n d i t i o n s . Re cen t advancements i n mus c l e t e s t i n g t e c h n i q u e s , i n p a r t i c u l a r t h e deve l opmen t of an i s o k i n e t i c dynamometer wh i c h can a s s e s s c o n c e n t r i c and e c c e n t r i c m u s c l e s t r e n g t h , have made i t p o s s i b l e t o r e l a t e m u s c l e s t r e n g t h r e s u l t s w i t h f u n c t i o n a l a c t i v i t y . I t has been shown by W i n t e r (1983) t h a t o v e r one r u n n i n g s t r i d e t h e knee m u s c l e s a b s o r b a p p r o x i m a t e l y t h r e e and a h a l f t i m e s more ene rgy t h a n t h e y g e n e r a t e , w i t h t h e l a r g e s t amount of e c c e n t r i c a c t i v i t y i n t h e q u a d r i c e p s d u r i n g s t a n c e p h a s e . The i m p o r t a n c e of h i s f i n d i n g s d u r i n g r u n n i n g r e l a t e s t o t h e use of t h e i s o k i n e t i c - 3 - dynamometer and t he need t o be a b l e t o t e s t and t r a i n m u s c l e s d u r i n g c o n c e n t r i c and e c c e n t r i c c o n t r a c t i o n s . Purpose The pu rpo se o f t h i s s t u dy was t o d e t e r m i n e i f t h e r e was a d i f f e r e n c e i n t h e EMG p a t t e r n s o f t h e q u a d r i c e p s i n f e m a l e r u n n e r s w i t h p a t e l l o - f emo ra l p a i n syndrome compared t o a g roup o f f e m a l e r u n n e r s f r e e o f knee p a i n and w i t h normal l o w e r e x t r e m i t y a l i g n m e n t . S e c o n d a r i l y , t h i s s t u d y compared t h e peak c o n c e n t r i c and e c c e n t r i c t o r q u e o f t h e q u a d r i c e p s and h a m s t r i n g s a t an a n g u l a r v e l o c i t y o f 200°/s t o see i f t h e r e was a s i g n i f i c a n t d i f f e r e n c e between t h o s e g roups o f s u b j e c t s w i t h and w i t h o u t p a t e l l o f e m o r a l p a i n syndrome. - 4 - METHODOLOGY SUBJECTS Twenty f e m a l e r e c r e a t i o n a l r u n n e r s , aged 15-36 y e a r s , v o l u n t e e r e d t o t a k e p a r t i n t h i s s t u d y . Twe l ve o f t h e s u b j e c t s were p l a c e d i n t h e c o n t r o l g roup as t h e y had no c o m p l a i n t s o f knee p a i n , no p r e v i o u s l o w e r e x t r e m i t y s u r g e r y o r known m u s c u l o s k e l e t a l a b n o r m a l i t i e s , and ' n o r m a l ' l o w e r e x t r e m i t y a l i g n m e n t . They were e v a l u a t e d by t h e p h y s i c i a n s a t U . B . C . S p o r t s M e d i c i n e C l i n i c f o r Q -ang l e (S chambe rge r , 1 9 8 3 ) , r e a r f o o t and f o r e f o o t a l i g n m e n t ( J ames , 1 9 7 9 ) , t h e deg ree o f p r o n a t i o n (James e t a l . 1 9 7 8 ) , l e g l e n g t h , and a l i g n m e n t a t t h e knee (Lehmkuhl and S m i t h , 1 9 8 3 ) . Normal v a l u e s were c o n s i d e r e d t o be : Q -ang l e 15° o r l e s s , r e a r f o o t and f o r e f o o t v a r u s 4° o r l e s s , no o v e r p r o n a t i o n , l e g l e n g t h d i s c r e p a n c y l e s s t h a n one c e n t i m e t e r and no genu r e c u r v a t u m . These s u b j e c t s were r u n n i n g a t l e a s t 16 km/week (10 m i l e s / w e e k ) . The e x p e r i m e n t a l g roup c o n s i s t e d o f e i g h t s u b j e c t s who had been d i a g n o s e d as h a v i n g p a t e l l o f e m o r a l p a i n syndrome by t h e p h y s i c i a n s a t UBC S p o r t s M e d i c i n e C l i n i c . They c o m p l a i n e d o f r i g h t knee p a i n a r ound t h e p a t e l l a , and had t h e f o l l o w i n g l o w e r e x t r e m i t y m a l a l i g n m e n t f e a t u r e s : Q - ang l e 15° o r more , r e a r f o o t and f o r e f o o t a l i g n m e n t measures more t h a n 4° and o v e r p r o n a t i o n o f t h e r i g h t f o o t when w e i g h t - b e a r i n g . F u r t h e r m o r e t h e i r l e g l e n g t h and a l i g n m e n t a t t h e knee were a s s e s s e d . These s u b j e c t s were a l s o r u n n i n g p r i o r t o t h e o n s e t o f p a i n . - 5 - EXPERIMENTAL PROCEDURE Testing of Peak Torque The s u b j e c t s were t e s t e d on an i s o k i n e t i c dynamometer (KINCOM) t o d e t e r m i n e t h e peak t o r q u e o f t h e i r r i g h t q u a d r i c e p s and h a m s t r i n g s , d u r i n g f o u r c o n c e n t r i c and e c c e n t r i c c o n t r a c t i o n s . I l l u s t r a t i o n o f a s u b j e c t b e i n g t e s t e d f o r q u a d r i c e p s s t r e n g t h on t h e KINCOM. Each s u b j e c t was i n s t r u c t e d t o s i t w i t h h e r back a g a i n s t t h e back s u p p o r t o f t h e c h a i r , t h e p e l v i s was s t a b i l i z e d by s t r a p p i n g , and t he p o s t e r i o r a s p e c t o f t h e knee was p o s i t i o n e d a t t h e f r o n t o f t h e c h a i r . - 6 - P o s i t i o n i n g o f t h e s u b j e c t ' s l o w e r l e g a g a i n s t t h e f o r c e arm o f t h e mach ine f o l l o w e d t h e d i r e c t i o n o f G o s l i n and C h a r t e r i s ( 1 9 7 9 ) . S u b j e c t s were i n s t r u c t e d t o g r i p t h e s i d e s o f t h e s e a t f o r s u p p o r t d u r i n g t h e t e s t i n g . D u r i n g h a m s t r i n g s t e s t i n g a d d i t i o n a l s t a b i l i z a t i o n was p r o v i d e d by s t r a p p i n g t h e t h i g h t o t h e t a b l e . The s u b j e c t s were g i v e n s t a n d a r d i z e d i n s t r u c t i o n s and t hen f o u r submaximal t r i a l s were p e r f o rmed b e f o r e t h e maximal t e s t . The range o f m o t i o n f o r t h e knee movement was t h r o u g h an a r c o f 90° (5° - 95°) a t a v e l o c i t y o f 200°/s, n o n - g r a v i t y c o r r e c t e d . Each t e s t c o n s i s t e d o f a c o n c e n t r i c c o n t r a c t i o n and an e c c e n t r i c c o n t r a c t i o n , t h u s , t h e s u b j e c t had t o c o n c e n t r a t e on two c o n s e c u t i v e c o n t r a c t i o n s f o r each r e p e t i t i o n . Each s u b j e c t p e r f o rmed f o u r max imal r e p e t i t i o n s f o r each mus c l e g roup ( q u a d r i c e p s and h a m s t r i n g s ) w i t h v e r b a l en cou ragemen t . EMG Measurement The s u b j e c t s r a n on a t r e a d m i l l , f i r s t a t a speed t h a t was 80% o f t h e i r normal r u n n i n g pace and t h e n f o r a s e cond t r i a l a t 12 km/h ( 7 . 5 MPH) u n t i l 10 s t r i d e s were c o l l e c t e d by t h e c ompu t e r . The f i r s t t r i a l was used as a warm-up f o r t h e se cond r un a t 12 km/h . L i n e a r e n v e l o p e EMG s i g n a l s f r om t h e r i g h t v a s t u s m e d i a l i s , v a s t u s l a t e r a l i s and r e c t u s f e m o r i s , t o g e t h e r w i t h a f o o t s w i t c h s i g n a l , were d i g i t a l l y r e c o r d e d a t 100 Hz e a c h . S u r f a c e e l e c t r o d e s were p l a c e d o v e r t h e mo to r p o i n t s o f each o f t h e m u s c l e s ( D e l a g i e t a l . 1 9 7 5 ) , w i t h an i n t e r e l e c t r o d e s p a c i n g o f one c e n t i m e t e r . P r e p a r a t i o n o f t h e s k i n was a c c o r d i n g t o t h e methods d e s c r i b e d by B a s m a j i a n ( 1 9 7 9 ) . - 7 - I l l u s t r a t i o n o f a s u b j e c t r u n n i n g on t h e t r e a d m i l l w i t h s u r f a c e e l e c t r o d e s i n p l a c e . The b i o a m p l i f i e r (custom-made) had a f r e q u e n c y r ange o f 20-1000 H z , t h e g a i n was 1000, t h e i n p u t impedance was 10 megaohms and t h e common mode r e j e c t i o n r a t i o (CMRR) was g r e a t e r t h an 100 dB . The a m p l i f i e r u t i l i z e d a se cond o r d e r band -pa s s f i l t e r ( W i n t e r , p e r s o n a l c o m m u n i c a t i o n ) . Each s t r i d e p e r i o d was n o r m a l i z e d t o 100% and t hen ensemb le a v e r a g e d o v e r t h e 10 t r i a l s f o r each mus c l e and f o r each s u b j e c t by c o m p u t e r . - 8 - S t a n d a r d d e v i a t i o n s f o r each i n t e r v a l were a l s o c a l c u l a t e d . S u b s e q u e n t l y g r and ensemb le a v e r a g e s f o r each mus c l e and f o r a l l o f t h e s u b j e c t s i n each g roup were compu ted . Statistical Analysis A m u l t i v a r i a t e a n a l y s i s (MANOVA) was done t o d e t e r m i n e i f t h e r e was a d i f f e r e n c e between g r oups f o r t h e peak EMG a m p l i t u d e f r om each mus c l e ( v a s t u s m e d i a l i s , v a s t u s l a t e r a l i s and r e c t u s f e m o r i s ) d u r i n g s t a n c e . A s e cond MANOVA a n a l y s i s was p e r f o rmed t o d e t e r m i n e i f t h e r e was a d i f f e r e n c e between g roups f o r mus c l e s t r e n g t h (peak t o r q u e s ) i n t h e q u a d r i c e p s and h a m s t r i n g s , bo th c o n c e n t r i c a l l y and e c c e n t r i c a l l y . An a n a l y s i s o f t h e s t r e n g t h r e l a t i o n s h i p s between t h e q u a d r i c e p s and h a m s t r i n g s , as e x p r e s s e d as a r a t i o , was done by a t - t e s t t o d e t e r m i n e i f t h e r e was a d i f f e r e n c e between g r o u p s . The l e v e l f o r s i g n i f i c a n c e o f ea ch a n a l y s i s was s e t a t p < 0 . 0 5 . A v i s u a l a n a l y s i s o f t h e EMG d a t a was a l s o i n c l u d e d t o d e t e r m i n e i f t h e r e was a d i f f e r e n c e o f more t h a n _+ one s t a n d a r d d e v i a t i o n i n t h e p h a s i c p a t t e r n s o f t h e mus c l e a c t i v i t y when t h e e x p e r i m e n t a l g roup was compared t o t h e c o n t r o l g r o u p . F u r t h e r m o r e , each i n d i v i d u a l ' s EMG p r o f i l e was s upe r impo sed on t h e c o n t r o l g r o u p ' s g r and ensemb le a v e r age t o d e t e r m i n e i f t h e r e were d i f f e r e n c e s o f more t han + one s t a n d a r d d e v i a t i o n , i n t h e i r EMG p a t t e r n s . - 9 - RESULTS T a b l e I i s a summary o f t h e c h a r a c t e r i s t i c s and c l i n i c a l f i n d i n g s o f t h e s u b j e c t s i n each g r o u p . TABLE I D e s c r i p t i v e C h a r a c t e r i s t i c s o f t h e S u b j e c t s AGE ( r a n g e ) HEIGHT ( r a n g e ) WEIGHT ( r a n g e ) KM/WEEK ( r ange ) KNEE PAIN Q-ANGLE REARFOOT & FOREFOOT ALIGNMENT OVERPRONATION (n) C o n t r o l Group 12 20 - 32 y e a r s 155 cm - 175 cm 5 3 . 2 - 6 3 . 6 kg 19 - 56 No 15° o r l e s s 4° o r l e s s 4 m i l d E x p e r i m e n t a l Group 8 15 - 36 y e a r s 152 .5 cm - 167 . 5 cm 50 kg - 6 3 . 6 kg 8 - 4 0 Yes 15° o r more 4° o r more - 10 - F i g u r e 1 shows t h e g r and ensemb le a v e r a g e s o f each m u s c l e ' s EMG a c t i v i t y ( V . M . - v a s t u s m e d i a l i s , R . F . - r e c t u s f e m o r i s , V . L . - v a s t u s l a t e r a l i s ) f r om t h e 12 s u b j e c t s i n t h e c o n t r o l g r o u p . The s o l i d l i n e r e p r e s e n t s t h e g r and ensemb le a v e r age w h i l e t h e d o t t e d l i n e s a r e + one s t a n d a r d d e v i a t i o n . One hund red p e r c e n t o f t h e g a i t c y c l e i s f r om h e e l - s t r i k e t o i p s i l a t e r a l hee l s t r i k e . T o e - o f f o c c u r r e d between 29 and 45% o f t h e c y c l e . The a m p l i t u d e o f t h e c u r v e s i s measured i n m i l l i v o l t s . The g r and ensemb le a v e r a g e s o f v a s t u s m e d i a l i s and r e c t u s f e m o r i s r e p r e s e n t 11 EMG p r o f i l e s . The re were t e n EMG r e c o r d i n g s o b t a i n e d f o r t h e g r and ensemb le a v e r a g e o f v a s t u s l a t e r a l i s . F i g u r e 2 r e p r e s e n t s t h e g r and ensemb le a v e r a g e s o f each m u s c l e f o r t h e e i g h t s u b j e c t s i n t h e e x p e r i m e n t a l g r o u p . T o e - o f f o c c u r r e d between 30 and 50% o f t h e g a i t c y c l e . In t h e e x p e r i m e n t a l g r o u p , t h e r e were a t o t a l o f e i g h t EMG p r o f i l e s each f o r v a s t u s m e d i a l i s and v a s t u s l a t e r a l i s , w h i l e t h e number o f r e c o r d i n g s f o r r e c t u s f e m o r i s was s e v e n . F i g u r e 3 shows t h e g r and ensemb le a v e r age o f each m u s c l e f r om t h e e x p e r i m e n t a l g roup s upe r imposed on t h e r e s u l t s o f t h e c o n t r o l g r o u p . The s o l i d l i n e i s t h e g r and ensemb le a ve r age o f t h e c o n t r o l g r o u p , t h e d o t t e d l i n e s r e p r e s e n t ^ one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean, and t h e c r o s s e d l i n e i s t h e g r and ensemb le a v e r age o f t h e e x p e r i m e n t a l g r o u p . 0 . 6 0 . 5 > £ 0 . 4 0 . 3 _ J 0 . 2 > 0 . 1 0 . 0 0 6 0 5 > £ 0 4 0 3 0 2 cn 0 . 1 0 . 0 0 . 6 0 . 5 > £ 0 . 4 0 . 3 0 . 2 > 0 . 1 0 . 0 FIGURE 1 GRAND ENSEMBLE AVERAGES OF THE CONTROL GROUP "1 1 1 ' I I •I I "1 1 2 0 3 0 4 0 5 0 6 0 % C Y C L E - 1 1 1̂ 1 7 0 8 0 9 0 1 0 0 FIGURE 2 GRAND ENSEMBLE AVERAGES OF THE EXPERIMENTAL GROUP 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0 % C Y C L E 0 . 6 _ FIGURE 3 GRAND ENSEMBLE AVERAGES OF THE EXPERIMENTAL GROUP COMPARED TO THE CONTROL GROUP 4 0 5 0 6 0 % C Y C L E C O I 1 0 0 - 14 - A m u l t i v a r i a t e a n a l y s i s (MANOVA) o f t h e peak EMG a m p l i t u d e s o f each mus c l e d u r i n g s t a n c e showed no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between g r o u p s , and no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e when t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s were compa red . However , t h e a n a l y s i s d i d r e v e a l a s i g n i f i c a n t d i f f e r e n c e between t h e peak a m p l i t u d e s o f r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s and a s i g n i f i c a n t d i f f e r e n c e between r e c t u s f e m o r i s and t h e v a s t u s m e d i a l i s (p < 0 . 0 5 ) . TABLE II Summary o f Manova EMG Peak A m p l i t u d e f o r V a s t u s M e d i a l i s , V a s t u s L a t e r a l i s and R e c t u s F e m o r i s C o n t r o l Group v s E x p e r i m e n t a l Group d f 1,13 Between Groups N .S . (p = .114) Between M u s c l e s V a s t u s L a t e r a l i s / R e c t u s F e m o r i s p = .008 V a s t u s M e d i a l i s ^Rec tus F e m o r i s p = .007 V a s t u s M e d i a l i s ^Vas tu s L a t e r a l i s N. S . (p = .347) - 15 - S u b s e q u e n t l y , a t - t e s t was p e r f o r m e d f o r each mus c l e t o d e t e r m i n e i f t h e r e wou l d have been a s i g n f i c a n t d i f f e r e n c e between t h e c o n t r o l g roup and t h e e x p e r i m e n t a l g roup peak EMG a m p l i t u d e s i f o n l y one mus c l e had been t e s t e d i n t h e e x p e r i m e n t . TABLE III Summary o f T - t e s t V a s t u s M e d i a l i s C o n t r o l Group "x = 309 .18 d f = 17 t = 1.241 N .S . E x p e r i m e n t a l Group 7 = 238 .87 V a s t u s L a t e r a l i s C o n t r o l Group x = 457 . 40 d f = 16 t = 2 .196 p < .025 E x p e r i m e n t a l Group "x = 289 .87 R e c t u s F e m o r i s C o n t r o l Group x = 142 .82 d f = 16 t = 0 .244 N .S . E x p e r i m e n t a l Group "x = 137 I f v a s t u s l a t e r a l i s had been t h e o n l y mus c l e t e s t e d t h e r e wou l d have been a s i g n i f i c a n t d i f f e r e n c e between t h e peak EMG a m p l i t u d e s o f t h e two g roups (p < 0 . 0 5 ) . - 16 - In T a b l e IV t h e r e s u l t s o f t h e m u s c l e s t r e n g t h t e s t s on t h e i s o k i n e t i c dynamometer a r e s ummar i z ed . TABLE IV Mean Peak To rque V a l u e s (+ one s t a n d a r d d e v i a t i o n ) a t 200°/s f o r t h e R i g h t Q u a d r i c e p s and H a m s t r i n g s C o n t r o l Group (n=12) E x p e r i m e n t a l Group (n=8) Q u a d r i c e p s E c c e n t r i c C o n c e n t r i c 170 N.m 112 .6 N.m (+50 .33) (+22 .27 ) 139 .4 N.m 9 5 . 1 N.m (+47 .06) (+21 .36) H a m s t r i n g s E c c e n t r i c C o n c e n t r i c 116 .25 N.m 9 8 . 5 N.m (+26 .53 ) (+21 .85) 111 .4 N.m (+27 .25) 93.6- N.m (+17 .94) - 17 - T a b l e V i s a summary o f t h e m u l t i v a r i a t e a n a l y s i s o f t h e mean peak t o r q u e s when compared by g r o u p s , by m u s c l e s ( q u a d r i c e p s and h a m s t r i n g s ) and by c o n t r a c t i o n ( e c c e n t r i c and c o n c e n t r i c ) . TABLE Y Summary o f Manova Peak To rque V a l u e s - Group by M u s c l e by C o n t r a c t i o n d f 1, 18 Between Groups N .S . (p = .230) Between M u s c l e s p = .001 Between C o n t r a c t i o n s p < .001 Peak t o r q u e v a l u e s were d e f i n e d as t h e h i g h e s t r e c o r d e d v a l u e on any one o f f o u r r e p e t i t i o n s o f t h e mus c l e t e s t , r e g a r d l e s s o f i t s p o s i t i o n i n t h e range o f m o t i o n . The re was no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between t h e g r oups f o r t h e peak t o r q u e v a l u e s , a l t h o u g h t h e r e was a s i g n i f i c a n t d i f f e r e n c e between t h e peak t o r q u e s o f t h e h a m s t r i n g s and t h e q u a d r i c e p s when t hey were g r ouped by m u s c l e . The r e was a l s o a s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between t h e peak t o r q u e s o f c o n c e n t r i c and e c c e n t r i c c o n t r a c t i o n s . - 18 - H a m s t r i n g s / q u a d r i c e p s (H/Q) r a t i o s were c a l c u l a t e d f r om t h e peak t o r q u e v a l u e s o f b o t h t h e e c c e n t r i c and c o n c e n t r i c c o n t r a c t i o n s . T a b l e VI i s a summary o f t h e t - t e s t t o compare g r oups f o r each o f t h e r a t i o s . TABLE VI Summary o f T - t e s t Peak To rque - A n a l y s i s By R a t i o s H/Q RATIO CONCENTRIC CONTROL GROUP x = .88 d f = 18 t = - 1 . 6 0 N .S . (p = .127) EXPERIMENTAL GROUP x = 1.02 H/Q RATIO ECCENTRIC CONTROL GROUP x = .73 d f = 18 t = - 1 . 0 6 N .S . (p = .304) EXPERIMENTAL GROUP x = .87 The re was no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between t h e g r oups f o r e i t h e r t h e c o n c e n t r i c o r e c c e n t r i c H/Q r a t i o s . - 19 - T a b l e V I I i s a summary o f t h e number o f d e v i a t i o n s o f t h e ensemb le a v e r a g e s o u t s i d e o f + one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean, f o r t h e e x p e r i m e n t a l g roup and t h e c o n t r o l g r o u p . In a normal ( G a u s s i a n ) d i s t r i b u t i o n 68.26% o f t h e s u b j e c t s ' EMG p r o f i l e s w o u l d l i e w i t h i n + one s t a n d a r d d e v i a t i o n and 15.87% wou l d be above one s t a n d a r d d e v i a t i o n w h i l e 15.87% wou l d be l e s s t h an one s t a n d a r d d e v i a t i o n . To d e t e r m i n e i f t h e r e s u l t s o f t h e c o n t r o l g roup f o l l o w e d a normal d i s t r i b u t i o n , t h e EMG peak a m p l i t u d e s d u r i n g s t a n c e phase f o r a l l t h r e e m u s c l e s and sw i ng phase f o r r e c t u s f e m o r i s f r om each s u b j e c t i n t h e c o n t r o l g roup were compared t o t h e mean EMG p a t t e r n +_ one s t a n d a r d d e v i a t i o n . S u b s e q u e n t l y t h e same EMG a m p l i t u d e s f r om each s u b j e c t i n t h e e x p e r i m e n t a l g roup were compared t o t h e c o n t r o l g r o u p ' s g r and ensemb le a v e r age +_ one s t a n d a r d d e v i a t i o n t o d e t e r m i n e i f t h e r e were more d e v i a t i o n s ( o u t s i d e + one s t a n d a r d d e v i a t i o n ) i n t h e EMG p r o f i l e s o f t h e g roup o f s u b j e c t s w i t h p a t e l l o f e m o r a l p a i n syndrome t han one wou l d e x p e c t i n a normal d i s t r i b u t i o n . - 20 - TABLE VII Deviations of the EMG Peak Amplitudes Compared to the Control Group's Grand Ensemble Average V a s t u s m e d i a l i s ( s t a n c e phase) w i t h i n +_ 1 S . D . above 1 S . D . be low 1 S . D . C o n t r o l Group 6/11 * 3/11 2/11 E x p e r i m e n t a l Group 6/8 2/8 R e c t u s f e m o r i s ( s t a n c e phase) w i t h i n + 1 S . D . above 1 S . D . be low 1 S . D . 5/11 4 /11 2/11 4/7 2/7 1/7 ( sw i ng phase) w i t h i n + 1 S .D . above 1 S .D . be l ow 1 S .D . 6/11 3/11 2/11 2/7 5/7 V a s t u s l a t e r a l i s ( s t a n c e phase) w i t h i n + 1 S .D . above 1 S .D . be l ow 1 S .D . 6/10 2/10 2/10 4/8 4/8 S i x s u b j e c t s o u t o f 11 r ema i ned w i t h i n + one s t a n d a r d d e v i a t i o n ( S . D . ) - 21 - DISCUSSION Group Mean Muscle Activation Patterns The r e s u l t s o f t h e c o m p a r i s o n o f t h e g r a n d ensemb le a v e r a g e s o f t h e q u a d r i c e p s m u s c l e s ( t h e v a s t u s m e d i a l i s , r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s ) o f s u b j e c t s w i t h p a t e l l o f e m o r a l p a i n syndrome t o t h o s e s u b j e c t s w i t h normal l o w e r e x t r e m i t y a l i g n m e n t and no knee p a i n , showed t h a t t h e two g r oups had t h e same a ve r age p a t t e r n s o f m u s c l e a c t i v i t y w h i l e r u n n i n g on a t r e a d m i l l , v a r y i n g o n l y i n r e g a r d t o a m p l i t u d e ( F i g u r e 3 ) . The peak a m p l i t u d e d i f f e r e n c e was n o t s t a t i s t i c a l l y s i g n i f i c a n t ( T a b l e I I ) as t h e mean mus c l e p a t t e r n s o f t h e e x p e r i m e n t a l g roup r ema i ned w i t h i n _+ one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean. The mean m u s c l e p a t t e r n s r e v e a l e d t h a t t h e l a r g e s t amount o f q u a d r i c e p s a c t i v i t y o c c u r r e d i n e a r l y s t a n c e i n b o t h t h e c o n t r o l g roup and t he e x p e r i m e n t a l g r o u p . T h i s b u r s t o f a c t i v i t y c o i n c i d e s w i t h an ene rgy a b s o r b i n g phase by t h e knee e x t e n s o r s as t h e y a r e c o n t r a c t i n g e c c e n t r i c a l l y t o c o n t r o l knee f l e x i o n ( W i n t e r , 1983; R o b e r t s o n and T a u n t o n , 1982; R o b e r t s o n , i n p r e s s ) . W i n t e r (1983) and R o b e r t s o n ( i n p r e s s ) have a l s o r e p o r t e d f r om t h e i r power a n a l y s e s o f j o g g i n g and r u n n i n g , t h a t f r om m i d - s t a n c e u n t i l l a t e - s t a n c e t h e q u a d r i c e p s c o n t i n u e t o be a c t i v e b u t t h e y a r e c o n t r a c t i n g c o n c e n t r i c a l l y t o e x t e n d t h e k n e e . From t h e EMG r e s u l t s o f t h i s s t u d y i t wou l d appea r t h a t t h e v a s t u s med i a l i s and v a s t u s l a t e r a l i s c o n t r i b u t e most t o t h e a c t i v i t y o f t h e q u a d r i c e p s d u r i n g e a r l y s t a n c e , s i n c e r e c t u s f e m o r i s showed l e s s mus c l e a c t i v i t y a t t h i s t i m e i n t h e g a i t c y c l e . In t h e i r EMG s t u d y o f t h e l e g m u s c l e s d u r i n g t r e a d m i l l r u n n i n g , E l l i o t t and B l a n k s b y (1979) a l s o - 22 - r e p o r t e d t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s t o have l a r g e r a m p l i t u d e s d u r i n g s t a n c e phase t h a n r e c t u s f e m o r i s , howeve r , t h e i r r e s u l t s d i f f e r e d f r om t h i s s t u d y i n t h a t t h e y r e p o r t e d t h e v a s t u s m e d i a l i s t o have t h e g r e a t e s t peak a m p l i t u d e w h i l e t h i s s t u d y f o u n d t h e v a s t u s l a t e r a l i s t o have t h e most EMG a c t i v i t y . I t i s n o t known why t h e r e may be t h e d i f f e r e n c e i n t h e a m p l i t u d e s o f t h e two m u s c l e s between t h e two s t u d i e s , as E l l i o t t and B l a n k s b y a l s o had t h e i r f e m a l e s u b j e c t s ( aged 20 -28 y e a r s ) r un on a t r e a d m i l l a t a p p r o x i m a t e l y 12 km/h . The m a j o r d i f f e r e n c e between t h e s t u d i e s i s t h a t E l l i o t t and B l a n k s b y u sed a v e r a g e d i n t e g r a t e d EMG as a f o rm o f p r o c e s s i n g w h i l e t h i s s t u d y u t i l i z e d l i n e a r e n v e l o p e p r o c e s s i n g . D u r i n g sw i ng p h a s e , t h e r e was a s e cond b u r s t o f a c t i v i t y i n r e c t u s f e m o r i s b u t no f u r t h e r a c t i v i t y i n t h e v a s t u s m e d i a l i s o r t h e v a s t u s l a t e r a l i s . E l l i o t t and B l a n k s b y (1979) a l s o r e p o r t e d t h i s s e cond c u r v e w h i c h t h e y s u g g e s t e d i s t h e m u s c l e ' s c o n t r i b u t i o n t o h i p f l e x i o n . The d i f f e r e n t m u s c l e a c t i v a t i o n p a t t e r n o f r e c t u s f e m o r i s - h a v i n g two b u r s t s o f a c t i v i t y d u r i n g t h e g a i t c y c l e , w h i l e t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s have o n l y one - i s because i t i s a t w o - j o i n t m u s c l e . Schwab e t a l . (1983) have r e p o r t e d t h a t s u r f a c e e l e c t r o d e s a r e n o t s e n s i t i v e enough t o d e p i c t t h e EMG p a t t e r n o f s p e c i f i c m u s c l e s b u t r a t h e r a r e r e p r e s e n t a t i v e o f t h e a c t i v i t y o f a mus c l e g r o u p . However , t h e EMG p r o f i l e s f r om t h i s s t u d y i n d i c a t e t h a t t h e r e was a d i f f e r e n c e i n t h e a c t i v i t y p a t t e r n o f r e c t u s f e m o r i s d u r i n g r u n n i n g g a i t compared t o t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s . F u r t h e r m o r e , t h e r e was a s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between t h e peak EMG a m p l i t u d e s o f - 23 - r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s (p = 0 . 008 ) and r e c t u s f e m o r i s and t h e v a s t u s m e d i a l i s (p = 0 . 007 ) d u r i n g s t a n c e phase ( T a b l e I I ) . In summary, a c o m p a r i s o n o f t h e a v e r age EMG p a t t e r n s o f t h e e x p e r i - men ta l g roup t o t h e c o n t r o l g roup r e v e a l e d t h e p h a s i n g o f t h e p a t t e r n s t o be s i m i l a r . D i f f e r e n c e s i n t h e a m p l i t u d e o f t h e c u r v e s o f t h e two g r oups were f o u n d ; i n p a r t i c u l a r t h e a m p l i t u d e s o f t h e m u s c l e a c t i v i t y p a t t e r n s o f t h e e x p e r i m e n t a l g roup were o b s e r v e d t o be l e s s t h an t h a t o f t h e c o n t r o l g r o u p . However , t h e s e d i f f e r e n c e s were n o t f o u n d t o be s t a t i s t i c a l l y s i g n i f i c a n t . T h i s l a c k o f a s t a t i s t i c a l d i f f e r e n c e may have r e s u l t e d f o r d i f f e r e n t r e a s o n s . I t may be t h a t t h e d i f f e r e n c e s i n t h e mus c l e a c t i v a t i o n p a t t e r n s between a ' n o r m a l ' g roup o f r u n n e r s and a g roup o f r u n n e r s w i t h PFPS a r e t o o s u b t l e f o r t h e EMG t o r e c o r d even though t h e l i t e r a t u r e has s u g g e s t e d t h a t t h e r e may be q u a d r i c e p s weakness a s s o c i a t e d w i t h P FPS , and more s p e c i f i c a l l y weakness o f v a s t u s m e d i a l i s (LeVeau & R o g e r s , 1980; F o x , 1 9 7 5 ) . R i c h a r d s e t a l . (1985) have s u g g e s t e d t h a t t h e a l t e r e d g a i t o f a s e v e r e l y d i s a b l e d p e r s o n w i l l r e s u l t i n changes i n t h e t i m i n g o f t h e EMG p a t t e r n s , however , t h e g a i t o f p a t i e n t s w i t h PFPS i s n o t u s u a l l y s e v e r e l y a f f e c t e d by t h e i r c o n d i t i o n , and i n t h e c a s e o f t h e s u b j e c t s i n t h i s s t u d y many were s t i l l r u n n i n g . I t may a l s o be t h a t a v e r a g i n g t h e EMG p a t t e r n s o f i n d i v i d u a l s w i t h a c l i n i c a l c o n d i t i o n o n l y a v e r a g e s t h e d i f f e r e n c e s o f each o f t h o s e s u b j e c t s . C l i n i c a l l y i t wou l d be more b e n e f i c i a l t o a n a l y z e each i n d i v i d u a l ' s r e s u l t s compared t o a ' n o rm ' t o d e t e r m i n e how o r i f t h e p a t i e n t d i f f e r s , and t h e n t r e a t m e n t c o u l d be d i r e c t e d t o c o r r e c t i n g t h e p r o b l e m . - 24 - Peak Concentric and Eccentric Torque Values of the Knee Extensor and F1exor Muscles The r e s u l t s show t h a t t h e r e was no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between t h e s u b j e c t s w i t h PFPS and t h e g roup o f s u b j e c t s f r e e o f knee p a i n and w i t h normal a l i g n m e n t when t h e mean peak c o n c e n t r i c and e c c e n t r i c t o r q u e v a l u e s were compared , f o r b o t h t h e r i g h t q u a d r i c e p s and h a m s t r i n g s . To d a t e t h e r e have been few s t u d i e s o f t h e q u a d r i c e p s and h a m s t r i n g s t o r q u e s a t c e r t a i n v e l o c i t i e s i n young women, and o f t h e s e few t h e y have o n l y i n v e s t i g a t e d c o n c e n t r i c m u s c l e a c t i v i t y . Wya t t & Edwards (1981) s t u d i e d 50 n o n - a t h l e t i c f e m a l e s u b j e c t s aged 25 - 34 y e a r s , a t t h r e e a n g u l a r v e l o c i t i e s . They f ound a t 180°/s t h a t t h e g r o u p ' s mean peak t o r q u e s were 57 f t - l b s . (77 N.m) f o r t h e q u a d r i c e p s and 45 f t - l b (61 N.m) f o r t h e h a m s t r i n g s . D i b r e z z o e t a l . (1985) s t u d i e d 241 n o n - a t h l e t i c f e m a l e s aged 18 - 28 y e a r s b u t o n l y a t 60°/s . B e r g e t a l . (1985) s t u d i e d 13 f e m a l e c o l l e g e b a s k e t b a l l p l a y e r s and f ound t h e i r mean peak t o r q u e s t o be 78 .7 f t - l b ( 107 N.m) f o r t h e r i g h t knee e x t e n s o r s and 5 6 . 3 f t - l b ( 76 N.m) f o r t h e r i g h t knee f l e x o r s a t 180°/s. R i c h a r d s (1981) s t u d i e d 19 f e m a l e s whose ages r anged f r om 21 - 60 y e a r s whose a c t i v i t y l e v e l s were no t s t a t e d , and she r e p o r t e d t h e i r mean peak t o r q u e f o r t h e q u a d r i c e p s t o be 8 0 . 9 N.m and f o r t h e h a m s t r i n g s t o be 4 8 . 1 N.m, a t 180°/s. A l l o f t h e s e s t u d i e s used t h e Cybex I I i s o k i n e t i c dynamometer , and i n each c a s e t h e s u b j e c t s were t e s t e d i n s i t t i n g w i t h a back s u p p o r t . Each g roup o f i n v e s t i g a t o r s a l s o p r e s e n t e d t h e i r r e s u l t s as a h a m s t r i n g s / q u a d r i c e p s r a t i o (H/Q r a t i o ) - t h a t i s t h e peak t o r q u e o f - 25 - c o n c e n t r i c knee f l e x i o n d i v i d e d by t h e peak t o r q u e o f c o n c e n t r i c knee e x t e n s i o n . In t h i s c a s e a t an a n g u l a r v e l o c i t y o f 180°/s Wya t t & Edwards r e p o r t e d a r a t i o o f . 7 9 , B e r g e t a l . r e p o r t e d .72 and R i c h a r d s f o und a r a t i o o f . 6 0 . The d i f f e r e n c e i n t h e r a t i o ' s may be due t o t h e d i f f e r e n t a c t i v i t y l e v e l s and t h e d i f f e r e n t age g roups o f t h e s u b j e c t s i n each s t u d y . The t e s t i n g f o r t h i s s t u d y was p e r f o r m e d on a KINCOM a t an a n g u l a r v e l o c i t y o f 200°/s w i t h t h e s u b j e c t s s e a t e d and s u p p o r t e d by a b a c k r e s t . The g r a v i t y c o r r e c t i o n o p t i o n was n o t used so t h a t c o m p a r i s o n s c o u l d be made t o o t h e r s t u d i e s . Those f e m a l e s who were r u n n i n g a minimum o f 16 km week (10 m i l e s / w e e k ) and who were f r e e o f l o w e r e x t r e m i t y a b n o r m a l i t i e s and p a i n had a c o n c e n t r i c mean peak t o r q u e o f 112 .6 N.m f o r t h e r i g h t q u a d r i c e p s and 9 8 . 5 N.m f o r t h e r i g h t h a m s t r i n g s . The mean H/Q r a t i o o f t h i s g roup was . 8 8 . Nosse (1982) r e v i e w e d 50 r e p o r t s o f h a m s t r i n g s / q u a d r i c e p s r a t i o s and f ound t h a t t h e r a t i o s v a r i e d f r om .43 - . 9 0 , unde r a v a r i e t y o f c o n d i t i o n s . He s u g g e s t e d t h a t i t i s n e c e s s a r y t o c o n s i d e r t h e a n g u l a r v e l o c i t y o f t h e t e s t , t h e t e s t i n g p o s i t i o n , t h e equ i pmen t u sed and t h e p o p u l a t i o n b e i n g i n v e s t i g a t e d b e f o r e c ompa r i n g o r g e n e r a l i z i n g f r om one s t u d y t o a n o t h e r . Appen & Duncan (1986) e l a b o r a t e f u r t h e r on s u b j e c t c h a r a c t e r i s t i c s , s u g g e s t i n g t h a t s e x , age , a c t i v i t y l e v e l and t y p e o f a c t i v i t y a l s o i n f l u e n c e t h e t o r q u e v a l u e s . They have f o u n d i n t h e i r r e s e a r c h t h a t a t h i g h c o n c e n t r i c v e l o c i t i e s (300°/s) , t h e r e was a s i g n i f i c a n t d i f f e r e n c e between t y p e s o f c o m p e t i t o r s , w h i c h may i n d i c a t e t h a t f i b r e t y p e c o m p o s i t i o n o r f i b r e s i z e i s a f a c t o r i n peak t o r q u e - 26 - v a l u e s . F u r t h e r m o r e , t h e y n o t e d t h a t g r a v i t y a f f e c t s t h e measured t o r q u e s . A t each o f f o u r a n g u l a r v e l o c i t i e s (60°/s, 180°/s, 240°/s and 300°/s) t h e g r a v i t y c o r r e c t e d peak e x t e n s o r t o r q u e s were i n c r e a s e d compared t o t h e n o n g r a v i t y c o r r e c t e d t o r q u e s , w h i l e t h e g r a v i t y c o r r e c t e d f l e x o r peak t o r q u e s d e c r e a s e d . These d i f f e r e n c e s r e s u l t e d i n a s i g n i f i c a n t d i f f e r e n c e between t h e H/Q r a t i o s c o r r e c t e d and n o t c o r r e c t e d f o r g r a v i t y , w i t h t h e g r a v i t y c o r r e c t e d t o r q u e s l o w e r . As more s t u d i e s a r e p u b l i s h e d i t becomes a p p a r e n t t h a t t h e r e i s a need f o r b a s e l i n e o r normal d a t a f r om w e l l d e l i n e a t e d p o p u l a t i o n s w i t h w e l l d e f i n e d t e s t i n g p r o t o c o l s , so t h a t c o m p a r i s o n s can be made. Compar ing t h e r e s u l t s o f t h i s s t u d y ' s g roup o f f e m a l e r u n n e r s ( w i t h o u t PFPS) t o t h e non- a t h l e t i c f e m a l e s i n Wya t t & E d w a r d ' s s t u d y , t h e peak t o r q u e v a l u e s f o r t h e r u n n e r s were h i g h e r f o r b o t h t h e q u a d r i c e p s and h a m s t r i n g s , as wou l d be e x p e c t e d c o m p a r i n g a c t i v e and n o n - a c t i v e p o p u l a t i o n s . , In B e r g & c o w o r k e r s ' s t u dy t h e f e m a l e b a s k e t b a l l p l a y e r s had a mean H/Q r a t i o l e s s t h an t h e r e c r e a t i o n a l r u n n e r s f r om t h i s s t u d y , w h i c h was d e m o n s t r a t e d by t h e f a c t t h a t t h e mean peak e x t e n s o r t o r q u e s were n e a r l y t h e same (107 N.m compared t o 112 .6 N.m r e s p e c t i v e l y ) b u t t h e mean peak f l e x o r t o r q u e s had a g r e a t e r s p r e a d between them. The mean peak f l e x o r t o r q u e o f t h e b a s k e t b a l l p l a y e r s was l e s s t h a n t h a t o f t h e r u n n e r s (76 N.m compared t o 9 8 . 5 N .m) . T h i s c o m p a r i s o n i s i n d i c a t i v e o f d i f f e r e n c e s i n t y p e s o f a c t i v i t y and a c t i v i t y l e v e l s . However , one can n o t r u l e o u t t h a t t y p e s o f equ i pmen t ( i . e . , - Cybex v s K incom) may a l s o be c o n t r i b u t i n g t o t h e d i f f e r e n c e s . - 27 - A n o t h e r pu r po se o f e s t a b l i s h i n g n o r m a t i v e d a t a i s so t h a t c o m p a r i s o n s can be made t o c l i n i c a l f i n d i n g s . Campbe l l and G l e n n (1982) s t u d i e d t h e r e s u l t s o f r e h a b i l i t a t i o n i n ma le and f e m a l e p a t i e n t s w i t h c h o n d r o m a l a c i a , and o t h e r knee p r o b l e m s , and r e p o r t e d t h e mean peak t o r q u e s o f t h e knee m u s c l e s o f t h e i n v o l v e d l e g b e f o r e t r e a t m e n t t o be l e s s t h a n t h e same m u s c l e s o f t h e n o n - i n v o l v e d l i m b . R i c h a r d s e t a l . (1985) compared t h e mean peak knee e x t e n s o r and f l e x o r t o r q u e s o f r h e u m a t o i d a r t h r i t i c p a t i e n t s ( f u n c t i o n a l c l a s s I I ) t o a ' n o r m a l ' g r o u p , and f ound s i g n i f i c a n t d i f f e r e n c e s between t h e two g r o u p s . The r e s u l t s o f t h i s s t u d y have shown t h e c o n c e n t r i c mean peak t o r q u e s o f t h e q u a d r i c e p s and h a m s t r i n g s i n t h o s e p a t i e n t s w i t h PFPS ( T a b l e IV) n o t t o be s i g n i f i c a n t l y d i f f e r e n t f r om t h e c o n t r o l g roup ( T a b l e V ) . The r e s u l t s o f t h e s e s t u d i e s i n d i c a t e t h a t t h e c au se o f p a i n and t h e a c t i v i t y l e v e l a l l o w e d by a d i s a b i l i t y o r d y s f u n c t i o n o f t h e m u s c u l o s k e l e t a l s y s t em a r e i m p o r t a n t c o n s i d e r a t i o n s i n a n a l y z i n g t e s t r e s u l t s . One wou l d e x p e c t p a t i e n t s w i t h t h e d i s a b l i n g d i s e a s e o f r h e u m a t o i d a r t h r i t i s t o have s i g n i f i c a n t l y l e s s mus c l e s t r e n g t h compared t o a c o n t r o l g r o u p , w h i l e t h o s e p a t i e n t s w i t h PFPS a r e s t i l l r e l a t i v e l y a c t i v e a l t h o u g h t h e y may n o t be r u n n i n g as a f o rm o f e x e r c i s e . T h i s b r i n g s f o r t h t h e need t o d e t e r m i n e what i s c l i n i c a l l y s i g n i f i c a n t f o r each c o n d i t i o n . G o s l i n and C h a r t e r i s (1979) b e l i e v e t h a t t h e H/Q r a t i o c o u l d be an i n d i c a t o r o f c l i n i c a l a b n o r m a l i t y a t t h e knee o r an i n d i c a t o r o f t h e p o t e n t i a l f o r i n j u r y . T h i s r a t i o i s s p e e d - s p e c i f i c , as t h e a n g u l a r v e l o c i t y i n c r e a s e s t h e d i f f e r e n c e s between t h e c o n c e n t r i c peak t o r q u e s o f t h e q u a d r i c e p s and h a m s t r i n g s d e c r e a s e s (Wya t t and Edwa rds , 1 9 8 1 ) . The - 28 - c o n c e n t r i c H/Q r a t i o f r om t h i s s t u d y o f .88 f o r t h e c o n t r o l g roup a t an a n g u l a r v e l o c i t y o f 200°/s, s u g g e s t s t h a t t h e peak t o r q u e d i f f e r e n c e s between t h e two mus c l e g r oups i s n o t g r e a t . The c o n c e n t r i c H/Q r a t i o f r om t h o s e s u b j e c t s w i t h PFPS was 1.02 ( T a b l e V I ) w h i c h was no t s t a t i s t i c a l l y d i f f e r e n t f r om t h e c o n t r o l g roup b u t w h i c h i s o u t s i d e o f t h e range r e p o r t e d by Nosse ( 1 9 8 2 ) . T h i s H/Q r a t i o s u g g e s t s t h a t on t h e a v e r age t h e s u b j e c t s w i t h PFPS had s i m i l a r s t r e n g t h i n t h e h a m s t r i n g s as i n t h e q u a d r i c e p s . The o n l y e c c e n t r i c i n v e s t i g a t i o n o f i s o k i n e t i c m u s c l e a c t v i t y f o und i n t h e l i t e r a t u r e i s t h a t by Komi (1973) d u r i n g w h i c h he s t u d i e d t h e e l bow f l e x o r s . He f ound t h a t as v e l o c i t y o f c o n t r a c t i o n i n c r e a s e d , t h e c o n c e n t r i c f o r c e d e c r e a s e d and t h e e c c e n t r i c f o r c e i n c r e a s e d . From t h e r e s u l t s o f t h i s s t u d y , a t 200°/s, t h e e c c e n t r i c mean peak t o r q u e s f o r b o t h t h e c o n t r o l g roup and t h e e x p e r i m e n t a l g roup were h i g h e r t h a n t h e c o n c e n t r i c mean peak t o r q u e s f o r t h e same m u s c l e s ( T a b l e I V ) . The r e s u l t s s u g g e s t t h a t f u r t h e r s t u d y i s n e c e s s a r y t o d e t e r m i n e i f a s i m i l a r f o r c e - v e l o c i t y r e l a t i o n s h i p e x i s t s i n c l i n i c a l c o n d i t i o n s ( s u c h as PFPS) as w e l l as i n t h e m u s c l e s o f normal h e a l t h y s u b j e c t s . A l t h o u g h t h e r e a r e no o t h e r s t u d i e s w h i c h have r e p o r t e d e c c e n t r i c peak t o r q u e s o f t h e q u a d r i c e p s and h a m s t r i n g s w i t h w h i c h t o compare , i t i s v a l u a b l e t o no t e t h e f i n d i n g s f r om t h i s s t u d y f o r t h e c o n t r o l g roup and t h e e x p e r i m e n t a l g r oup ( T a b l e IV) so t h a t f u t u r e c o m p a r i s o n s c an be made. S i m i l a r l y t h e r e has been no l i t e r a t u r e on t h e e c c e n t r i c H/Q r a t i o . The re was n o t a s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between t h e two g roups when c ompa r i n g e c c e n t r i c H/Q r a t i o s i n t h i s s t u d y , however , as - 29 - p r e v i o u s l y s t a t e d i t i s u s e f u l t o n o t e t h e r a t i o s ( T a b l e V I ) f o r f u t u r e c o m p a r i s o n s . I t i s i n t e r e s t i n g t o no t e f r om t h e r e s u l t s t h a t t h e c o n c e n t r i c and e c c e n t r i c mean peak t o r q u e v a l u e s o f t h e h a m s t r i n g s f o r b o t h s u b j e c t g roups a r e c l o s e r t o g e t h e r w h i l e t h e mean peak t o r q u e s o f each g roup f o r t h e q u a d r i c e p s a r e much f a r t h e r a p a r t ( T a b l e I V ) . In summary, t h e r e s u l t s o f o u r i s o k i n e t i c t e s t i n g have r e v e a l e d t h a t - i ) t h e mean c o n c e n t r i c H/Q r a t i o ( 1 . 0 2 ) o f t h o s e s u b j e c t s w i t h PFPS was above t h e r ange t h a t has been r e p o r t e d i n t h e l i t e r a t u r e . T h i s a b n o r m a l l y h i g h r a t i o s u g g e s t e d t h a t t h e mean peak t o r q u e o f t h e h a m s t r i n g s was n e a r l y t h e same as t h e mean peak t o r q u e o f t h e q u a d r i c e p s . i i ) a t an a n g u l a r v e l o c i t y o f 200°/s t h e c o n c e n t r i c and e c c e n t r i c H/Q r a t i o s were d i f f e r e n t , due t o t h e f a c t t h a t t h e c o n c e n t r i c and e c c e n t r i c mean peak t o r q u e s o f t h e h a m s t r i n g s were c l o s e r t o g e t h e r w h i l e t h e c o n c e n t r i c and e c c e n t r i c mean peak t o r q u e s o f t h e q u a d r i c e p s had a g r e a t e r s p r e a d between them. - 30 - i i i ) when c o n s i d e r i n g c l i n i c a l f i n d i n g s compared t o no rms , i t a ppea r s t h a t c l i n i c a l s i g n i f i c a n c e d i f f e r s f r om s t a t i s t i c a l s i g n i f i c a n c e , and t h a t each c o n d i t i o n may have a d i f f e r e n t l e v e l o f s i g n i f i - c an ce d epend i ng upon p a i n , m u s c u l o s k e l e t a l i n v o l v e m e n t and deg ree o f d i s a b i l i t y . - 31 - CONCLUSIONS The r e s u l t s o f t h i s s t u dy have shown t h a t : 1. From a v i s u a l a n a l y s i s o f t h e mean EMG p r o f i l e s o f t h e e x p e r i m e n t a l g roup s upe r imposed on t h e c o n t r o l g r o u p ' s mean EMG p a t t e r n + one s t a n d a r d d e v i a t i o n , t h e mean mus c l e a c t i v i t y o f t h e v a s t u s m e d i a l i s , r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s was s i m i l a r ( w i t h i n +̂  one s t a n d a r d d e v i a t i o n ) f o r s u b j e c t s w i t h p a t e l l o f e m o r a l p a i n syndrome compared t o s u b j e c t s f r e e o f knee p a i n and w i t h normal l o w e r e x t r e m i t y a l i g n m e n t , d u r i n g t r e a d m i l l r u n n i n g . A d d i t i o n a l l y , a m u l t i v a r i a t e a n a l y s i s (MANOVA), o f t h e peak EMG a m p l i t u d e s r e v e a l e d t h a t t h e r e was n o t a s i g n i f i c a n t d i f f e r e n c e between t h e two g r o u p s . 2 . The mean EMG p a t t e r n f o r r e c t u s f e m o r i s f r om bo t h g roups was d i f f e r e n t f r om t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s , i n t h a t r e c t u s f e m o r i s had a b u r s t o f a c t i v i t y d u r i n g s t a n c e phase and a second b u r s t o f a c t i v i t y d u r i n g s w i n g , w h i l e t h e v a s t u s med i a l i s and t h e v a s t u s l a t e r a l i s had o n l y one b u r s t o f a c t i v i t y d u r i n g s t a n c e p h a s e . F u r t h e r m o r e , t h e r e was a s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e i n t h e peak EMG a m p l i t u d e s o f r e c t u s f e m o r i s compared t o t h e v a s t u s m e d i a l i s and r e c t u s f e m o r i s compared t o t h e v a s t u s l a t e r a l i s d u r i n g s t a n c e p h a s e . 3 . The r e was no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between t h e s u b j e c t s w i t h and w i t h o u t p a t e l l o f e m o r a l p a i n syndrome when t h e i r - 32 - mean peak c o n c e n t r i c and e c c e n t r i c t o r q u e v a l u e s were compared f o r t h e r i g h t h a m s t r i n g s and q u a d r i c e p s . S i m i l a r l y a t - t e s t o f t h e peak t o r q u e v a l u e s e x p r e s s e d as a h a m s t r i n g s / q u a d r i c e p s r a t i o showed t h a t t h e r e was no t a s i g n i f i c a n t d i f f e r e n c e between t h e g r o u p s . However , t h e mean c o n c e n t r i c H/Q r a t i o f r om t h e s u b j e c t s w i t h PFPS was 1.02 wh i c h i s o u t s i d e o f t h e normal r ange wh i c h has been r e p o r t e d i n t h e l i t e r a t u r e . - 3 3 - RECOMMENDATIONS Based on t h e u n d e r s t a n d i n g g a i n e d as a r e s u l t o f t h i s s t u d y , t h e f o l l o w i n g recommenda t i ons a r e s u g g e s t e d f o r f u t u r e i n v e s t i g a t i o n s . 1. The s i z e o f t h e c o n t r o l g roup must be g r e a t e r so t h a t t h e mean EMG p r o f i l e + one s t a n d a r d d e v i a t i o n f r om each mus c l e wou l d have l e s s v a r i a b i l i t y and b e t t e r r e p r e s e n t a normal d i s t r i b u t i o n . 2. A c t i v i t i e s su ch a s a s c e n d i n g o r d e s c e n d i n g s t a i r s o r s q u a t t i n g may r e v e a l g r e a t e r d i f f e r e n c e s i n t h e EMG p r o f i l e s o f t h o s e s u b j e c t s w i t h p a t e l l o f e m o r a l p a i n syndrome compared t o a c o n t r o l g r o u p , as t h e j o i n t r e a c t i o n f o r c e s t h r o u g h t h e p a t e l l o f e m o r a l j o i n t a r e known t o be h i g h d u r i n g t h o s e a c t i v i t i e s and p a t i e n t s o f t e n c o m p l a i n o f p a i n d u r i n g t h o s e a c t i v i t i e s . 3 . By r e c o r d i n g t h e EMG a c t i v i t y o f t h e m u s c l e s s i m u l t a n e o u s l y w i t h t h e mus c l e t e s t i n g and t h en r e c o r d i n g t h e m u s c l e a c t i v i t y d u r i n g a f u n c t i o n a l a c t i v i t y w i t h o u t r emov ing t h e e l e c t r o d e s , t h e i n v e s t i g a t o r wou l d be a b l e t o d e t e r m i n e t h e p e r c e n t a g e o f mus c l e a c t i v i t y d u r i n g a c t i v i t y compared t o a max imal s t r e n g t h t e s t . 4. F u r t h e r s t u d y may i n v o l v e p r e - t r e a t m e n t and p o s t - t r e a t m e n t EMG and mus c l e s t r e n g t h e v a l u a t i o n o f p a t i e n t s w i t h p a t e l l o f e m o r a l p a i n syndrome. - 34 - REFERENCES A n d e r s o n , J . E . , e d . G r a n t ' s A t l a s o f Ana tomy. V I I I E d i t i o n . W i l l i a m s and W i l k i n s C o . , B a l t i m o r e . 1983 . Appen , E . L . , Duncan , P.W. 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P h y s i c a l T h e r a p y . 6 1 : 9 2 5 - 9 2 7 . 1 9 8 1 . P e r r y , J . E a s t e r d a y , C , A n t o n e l l i , D. S u r f a c e v s i n t r a m u s c u l a r e l e c t r o d e s f o r e l e c t r o m y o g r a p h y o f s u p e r f i c i a l and deep m u s c l e s . P h y s i c a l T h e r a p y . 6 1 : 7 - 1 5 . 1 9 8 1 . - 37 - P o c o c k , G . E l e c t r o m y o g r a p h i c s t u d y o f t h e q u a d r i c e p s d u r i n g r e s i s t i v e e x e r c i s e . P h y s i c a l T h e r a p y . 4 3 : 4 2 7 - 4 3 4 . 1 9 6 3 . R e y n o l d s , L . , L e v i n , T . A . M e d e i r o s , J . M . , A d l e r , N . S . , H a l l u m , A . EMG a c t i v i t y o f t h e v a s t u s m e d i a l i s o b l i q u e and t h e v a s t u s l a t e r a l i s i n t h e i r r o l e i n p a t e l l a r a l i g n m e n t . A m e r i c a n J o u r n a l o f P h y s i c a l M e d i c i n e . 6 2 : 6 1 - 7 0 . 1 9 8 3 . R i c h a r d s , C . L . , Dynamic s t r e n g t h c h a r a c t e r i s t i c s d u r i n g i s o k i n e t i c knee movements i n h e a l t h y women. P h y s i o t h e r a p y Canada . 3 3 : 1 4 1 - 1 5 0 . 1 9 8 1 . R i c h a r d s , C . L . , W e s s e l , J . , M a l o u i n , F . M u s c l e a c t i v a t i o n p a t t e r n s i n g a i t o f r h e u m a t o i d a r t h r i t i c p a t i e n t s . P h y s i o t h e r a p y Canada . 3 7 : 2 2 0 - 2 2 8 . 1985 . R o b e r t s o n , D .G . E . F u n c t i o n s o f t h e l e g m u s c l e s d u r i n g s t a n c e phase i n r u n n i n g . In B i o m e c h a n i c s X . In p r e s s . R o b e r t s o n , D . G . E . , T a u n t o n , J . E . Power c h a r a c t e r i s t i c s o f l e g m u s c l e s d u r i n g s t a n c e phase o f r u n n i n g . P r o c e e d i n g s o f t h e Second B i a n n u a l C o n f e r e n c e o f t h e C a n a d i a n S o c i e t y f o r B i o m e c h a n i c s , 1982 . S chambe rge r , w. O r t h o t i c s f o r a t h l e t e s : A t t a c k i n g t h e b i o m e c h a n i c a l r o o t s o f i n j u r y . C a n a d i a n F a m i l y P h y s i c i a n . 2 9 : 1 6 7 0 - 1 6 8 0 . 1 9 8 3 . Schwab, G . H . , Moynes , D .R . , J o b , F .W. , P e r r y , J . Lower e x t r e m i t y e l e c t r o m y o g r a p h i c a n a l y s i s o f r u n n i n g g a i t . C l i n i c a l O r t h o p a e d i c s . 176: 1 6 6 - 1 7 0 . 1983 . T a u n t o n , J . E . , C l e m e n t , D . B . , S m a r t , G .W. , W i l e y , J . P . , M c N i c o l , K . L . A t r i p l a n a r e l e c t r o g o n i o m e t e r i n v e s t i g a t i o n o f r u n n i n g mechan i c s i n r u n n e r s w i t h c ompensa t o r y o v e r p r o n a t i o n . C a n a d i a n J o u r n a l o f A p p l i e d S p o r t S c i e n c e s . 10 : 1 0 4 - 1 1 5 . 1 985 . V r e d e n b r e g t , J . , R au , G . S u r f a c e e l e c t r o m y o g r a p h y i n r e l a t i o n t o f o r c e , mus c l e l e n g t h and e n d u r a n c e . In New Deve l opmen t s i n E l e c t r o m y o g r a p h y and C l i n i c a l N e u r o p h y s i o l o g y , p. 6 0 7 - 6 2 2 . E d i t e d by J . E . Desmedt . K a r g e r . B a s e l . 1973": - W i b e r g , G. R o e n t g e n o g r a p h ^ and ana t om i c s t u d i e s on t h e f e m o r o p a t e l l a r j o i n t . A c t a O r t h o p a e d i c a S c a n d i n a v i a . 12 : 3 1 9 - 4 1 0 . 1 9 4 1 . W i l d , J . , F r a n k l i n , T . , Woods, G . P a t e l l a r p a i n and q u a d r i c e p s r e h a b i l i t a t i o n . A m e r i c a n J o u r n a l o f S p o r t s M e d i c i n e . 10 : 1 2 - 1 5 . 1982 . W i n t e r , D .A . , B i o m e c h a n i c s o f Human Movement. J o hn W i l e y & S o n s , New Y o r k . 1979 . - 38 - W i n t e r , D.A. Movements o f f o r c e and m e c h a n i c a l power i n j o g g i n g . J . o f B i o m e c h a n i c s . 16 : 9 1 - 9 7 . 1 9 8 3 . W i n t e r , D.A. P a t h o l o g i c g a i t d i a g n o s i s w i t h c o m p u t e r - a v e r a g e d e l e c t r o - m y o g r a p h i c p r o f i l e s . A r c h i v e s o f P h y s i c a l M e d i c i n e and R e h a b i l i t a t i o n . 16: 9 1 - 9 7 . 1984 . W y a t t , M .P . , Edwa rds , A . M . Compa r i s on o f q u a d r i c e p s and h a m s t r i n g t o r q u e v a l u e s d u r i n g i s o k i n e t i c e x e r c i s e . J . o f O r t h o p a e d i c and S p o r t s P h y s i c a l T h e r a p y . 3 : 4 8 - 5 6 . 1 9 8 1 . APPENDIX 1 TABLE VIII C l i n i c a l C h a r a c t e r i s t i c s o f t h e C o n t r o l Group S u b j e c t s CS CR GG J F LS MR PB PW SL SO SP VA Age (years) He ight (cm) Weight (kg) Km/wk runn ing 20 155 60.9 19 22 155 54.5 24 20 167.5 58.1 56 21 160 54.5 16 27 165 60 56 32 170 53.6 24 25 172.5 56.4 32 21 160 53.2 24 29 165 63.6 40 23 175 63.6 40 25 170 54 19 26 167.5 53.2 48 Knee pa in no no no no no no no no no no no no Knee a l ignment va lgus va lgus va lgus varus varus varus varus varus varus va lgus varus va lgus Q-angle 12° 12° 10° 12° 12° 15° 15° 14° 12° 13° 12° 10° Rear foot varus a l ignment < 4° < 4° < 4° < 4° < 3° < 4° < 4° < 4° < 4° < 4° < 4° < 4 ° Fo re foo t varus a l i gnment < 4° < 4° < 4° < 4° < 3° <4° < 4° < 4° < 2° < 3° < 3° < 4 0 Overpronat ion no m i l d no m i l d m i l d no no m i l d no no no no Leg-1ength equal equal equal R<L 1cm* equal equal equal equal equal equal equal equal r i g h t l e g sho r t e r than l e f t by one cent imeter CO - 40 - Individual Ensemble Averages from the Control Group F i g u r e s 4 t o 15 a r e t h e ensemb le a v e r a g e s o f t h e l i n e a r e n v e l o p e EMG o f v a s t u s m e d i a l i s ( V . M . ) , r e c t u s f e m o r i s ( R . F . ) and v a s t u s l a t e r a l i s ( V . L . ) f o r each s u b j e c t i n t h e c o n t r o l g r o u p . The s o l i d l i n e r e p r e s e n t s t h e ensemb le a v e r a g e w h i l e t h e d o t t e d l i n e s a r e +_ one s t a n d a r d d e v i a t i o n . One hund red p e r c e n t o f t h e g a i t c y c l e i s f r om h e e l - s t r i k e t o i p s i l a t e r a l h e e l - s t r i k e . T o e - o f f i s i n d i c a t e d by A . The a m p l i t u d e o f t h e c u r v e s i s measu red i n m i l l i v o l t s . FIGURE 4 T 1 r 40 50 60 % C Y C L E 100 SUBJECT CR. FIGURE 5 > 0.4 J e ^ 0 . 3 . • 0.2 • 0 . 1 J ^• in i i-iMMiiHU . j \\\&WA 10 20 30 40 50 60 % C Y C L E 70 80 90 100 SUBJECT CS. FIGURE 6 3 0 4 0 5 0 6 0 % C Y C L E 7 0 8 0 9 0 1 0 0 SUBJECT GG FIGURE 7 a . 6 r\ 0 . 5 _ > 0 . 4 _ ^ 0 . 3 _ % C Y C L E SUBJECT JF FIGURE 8 0 . 6 r\ 0 . 5 _ > 0 . 4 _ £ 3 _ 2 _ > 0 1 _ 0 0 _ 0 6 _ ^ 0 . 5 _ > 0 . 4 _ ^ 0 . 3 _ 2 _ C 0 - 1 0 0 0 6 _ 0 5 _ > 0 4 _ £ 0 3 _ 0 2 _ 0 . 1 _ > 0 . 0 0 5 0 6 0 % C Y C L E 7 0 T 8 0 T 9 0 4^ in 1 0 0 SUBJECT LS FIGURE 9 T 4 0 5 0 6 0 % C Y C L E 1 0 0 SUBJECT MR FIGURE 10 r\ 0 . 5 _ > 0 . 4 _ ^ 0 . 3 _ • 0 . 2 a. 0 . 1 J 0 . 0 0 1 0 2 0 3 0 4 0 5 0 6 0 % C Y C L E "1 1 " • " I I 7 0 8 0 9 0 1 0 0 SUBJECT PB FIGURE 11 0.0 0.6 ^ 0.5 _ > 0 . 4 _ £ ^ 0 . 3 • 0 . 2 J 0 . 1 J ^ 0.5 J > 0. 4 ^ 0.3 _ ^ • 0 . 2 . > 0 . 1 J 0.0 0 ! ! 1 ^ * H J * * * ^ t i K j i i i i i i i i i | i i « i j . i - M : i . : | i m r H«*p 40 50 % CYCLE l i i l ; i i i | i i n i i i i i | i i 60 70 80 90 100 SUBJECT PW FIGURE 12 SUB.JECT SL FIGURE 13 0.6 r\ 0 . 5 _ > 0 . 4 _ E ^ 0 .3 _ ^ 0 . 5 _ > 0 . 4 _ % CYCLE SUBJECT SO FIGURE 14 0.6 ^ 0.5 J > 0 . 4 _ ^ 0 .3 _ ^ 0.5 _ > 0 . 4 _ ^ 0 .3 _ rx 0.5 _ > 0 . 4 _ ^ 0.3 _ 10 20 30 40 50 60 70 80 90 100 % CYCLE SUBJECT SP FIGURE 15 0*6 . ' 1 1 1 n 1 1 ' ~ ~ T 1 1 % C Y C L E SUBJECT VA - 53 - APPENDIX 2 TABLE IX I n d i v i d u a l Peak To rque V a l u e s f o r t h e R i g h t Leg a t 200°/s Q u a d r i c e p s H a m s t r i n g s SUBJECTS C o n t r o l Group C o n c e n t r i c E c c e n t r i c C o n c e n t r i c E c c e n t r i c CR 100 166 77 99 CS 98 197 104 132 GG 90 72 88 97 J F 137 172 139 154 LS 109 104 92 110 MR 122 198 103 125 PB 114 202 127 150 PW 90 169 74 92 SL 116 124 73 63 SO 129 193 115 135 SP 164 276 118 142 VA 82 168 72 96 imenta l Group SC 87 144 107 138 HB 128 84 111 120 EC 76 80 89 91 TR 78 110 66 66 RW 90 168 122 158 SS 114 233 96 121 JH 121 164 85 105 JG 67 132 73 92 - 54 - TABLE X I n d i v i d u a l C o n c e n t r i c and E c c e n t r i c H a m s t r i n g s / Q u a d r i c e p s R a t i o s F o r The R i g h t Leg SUBJECTS C o n t r o l Group C o n c e n t r i c E c c e n t r i c CR .77 .60 CS 1.06 .67 GG .98 1.35 J F 1.01 .90 LS .84 1.06 MR .84 .63 PB 1.11 .74 PW .82 .54 SL .63 .51 SO .89 .70 SP .72 .51 VA .88 .57 E x p e r i m e n t a l Group SC 1.23 .95 HB .87 1.43 EC 1.17 1.14 TR .85 .60 RW 1.36 .94 SS .84 .52 JH .70 .64 JG 1.09 .70 - 55 - APPENDIX 3 Individual Muscle Activation Patterns The c l i n i c a l e x a m i n a t i o n o f t h e e i g h t s u b j e c t s w i t h p a t e l l o f e m o r a l p a i n , p l u s t h e r e s u l t s o f t h e i r dynamic s t r e n g t h t e s t i n g i s summar i zed i n T a b l e X I . TABLE XI C l i n i c a l C h a r a c t e r i s t i c s and Dynamic S t r e n g t h o f t h o s e S u b j e c t s W i t h R i g h t P a t e l l o f e m o r a l P a i n Syndrome Age (years) He ight (cm) Weight (kg) Km/week runn ing Pa in - l o c a t i o n - du ra t i on - w i t h runni Knee a l ignment SC HB EC TR RW SS 23 24 22 15 35 20 165 167.5 160 155 167.5 160 56.8 63.6 53.6 54.5 59.1 61.4 24 19 40 8 19 24 JH JG 22 36 167.5 152.5 61.4 50 24 16 medial medial medial i n f r a - media l r e t r o - r e t r o - p a t e l l a r r e t r o - pa te ! 1 a r medial medial i n f r a p a t e l l a r l a t e r a l p a t e l l a r p a t e l l a r 6-7 y r s 5 y r s 3 mo 2 y r s 2-3 y r s 6 y r s ng yes yes yes yes yes yes va lgus va lgus va lgus r e c u r - varus varus vatum va lgus 2 y r s yes varus 6 mo yes va lgus Q-angle 15° 20° 20° 18° 20° 17° 20° 19° Rear foot varus a l ignment 3° 8° 8° 10° 6° 10° 4° 5° Fo r e f oo t varus a l ignment 10° 6° 10° 6° 4° 2° 4° 4° Overpronat ion y e s yes yes yes yes y e s yes yes Leg- length equal equal L<R 1 cm * equal equal L<R 1 cm* equal equal Peak torque (N.m) Quadr iceps - c on cen t r i c 87 128 76 78 90 114 121 67 - e c c e n t r i c 144 84 80 110 168 233 164 132 Hamstr ings - c on cen t r i c 107 111 89 66 122 96 85 73 - e c c e n t r i c 138 120 91 66 158 121 105 92 Hamstr ings/Quadr iceps r a t i o - c on cen t r i c 1.23 .87 1.17 .85 1.36 .84 .70 1.09 - e c c e n t r i c .95 1.43 1.14 .60 .94 .52 .64 .70 * l e f t l e g s ho r t e r than r i g h t by one cen t imete r - 56 - C e r t a i n r e s e a r c h e r s ( W i n t e r , 1984 , R i c h a r d s e t a l . 1985) b e l i e v e t h a t a v e r a g i n g t h e EMG p a t t e r n s o f s u b j e c t s w i t h a c l i n i c a l p r ob l em masks t h e i n d i v i d u a l d i f f e r e n c e s o f each p a t i e n t . I t i s t h e i r s u g g e s t i o n t h a t i n o r d e r t o e v a l u a t e c l i n i c a l d i f f e r e n c e s between p a t i e n t s and a c o n t r o l g r o u p , i t must be done on an i n d i v i d u a l b a s i s and no t by c ompa r i n g t h e p a t i e n t s as a g r o u p . W i n t e r (1984) p o i n t s o u t , howeve r , t h a t i n o r d e r t o use t h i s t e c h n i q u e a l a r g e d a t a bank o f normal s u b j e c t s ' m u s c l e a c t i v i t y i s r e q u i r e d p l u s imp roved n o r m a l i z a t i o n t e c h n i q u e s t o r e du ce t h e between - s u b j e c t v a r i a b i l i t y . In t h i s s t u d y t h e i n d i v i d u a l mus c l e a c t i v a t i o n p a t t e r n s o f t h o s e s u b j e c t s w i t h p a t e l l o f e m o r a l p a i n syndrome have been compared t o t h e c o n t r o l g r o u p , however t h e r e s u l t s must be v i ewed c a u t i o u s l y f o r d i f f e r e n t r e a s o n s . The s m a l l number o f s u b j e c t s i n t h e c o n t r o l g roup (n=12) has t h e p o s s i b i l i t y o f i n c r e a s i n g t h e v a r i a b i l i t y o f t h e r e s u l t s . As seen i n T a b l e V I I t h e mean EMG p a t t e r n s o f t h e s u b j e c t s i n t h e c o n t r o l g roup d i d n o t a lway s f a l l w i t h i n a normal ( G a u s s i a n ) d i s t r i b u t i o n , w h i c h makes a c o m p a r i s o n t o what i s c o n s i d e r e d a ' n o r m a l ' g roup ( t h e c o n t r o l g roup) n o t as s i g n i f i c a n t . I t i s a l s o i m p o r t a n t t o p o i n t o u t t h a t t h i s s t u d y has o n l y a d d r e s s e d and a t t e m p t e d t o r e l a t e t h e a l i g n m e n t f e a t u r e s , s t r e n g t h measu remen t s , c l i n i c a l s i g n s and symptoms and t h e EMG r e s u l t s o f each s u b j e c t . P a t e l l o - f emo r a l p a i n syndrome i s a c o m p l i c a t e d c l i n i c a l e n t i t y w i t h c o n s i d e r a b l e v a r i a t i o n i n i t s f e a t u r e s f r om p a t i e n t t o p a t i e n t , and t h e r e may have been c e r t a i n o t h e r c o n t r i b u t i n g f a c t o r s t h a t were no t a s s s e s s e d o r d i s c u s s e d . - 57 - These i n c l u d e t r a i n i n g e r r o r s , w h i c h a c c o r d i n g t o James e t a l . (1978) a c c o u n t f o r 60% o f t h e l o w e r e x t r e m i t y i n j u r i e s t o r u n n e r s . W i t h i n t h e c a t e g o r y o f t r a i n i n g e r r o r s t h e r e a r e such f a c t o r s as e x c e s s i v e m i l e a g e , t h e t y p e o f r u n n i n g s u r f a c e , a r a p i d change i n r u n n i n g r o u t i n e o r a sudden i n t e n s e w o r k o u t , any one o f w h i c h may p r o voke p a t e l l o f e m o r a l p a i n . A n o t h e r i m p o r t a n t a s p e c t i n t h e o c c u r r e n c e o f knee i n j u r i e s as a r e s u l t o f r u n n i n g i s f o o t w e a r . A r u n n e r who has e x c e s s i v e p r o n a t i o n o f t h e f o o t and who i s n o t w e a r i n g a w e l l s u p p o r t i n g shoe w i l l d e f o rm t h e shoe t o an e x t e n t t h a t w i l l i n d i c a t e t h e a d v e r s e s t r e s s e s a t t h e f o o t (James e t a l . 1 9 7 8 ) . These s t r e s s e s a r e o f t e n r e f l e c t e d up t o t h e k n e e . The re a r e o t h e r p o s s i b l e c l i n i c a l a n d / o r a n a t o m i c a l r e a s o n s f o r a n t e r i o r knee p a i n , w h i c h must be d i f f e r e n t i a t e d f r om p a t e l l o f e m o r a l p a i n syndrome. A s i d e f r om a t i g h t l a t e r a l r e t i n a c u l u m , p l i c a , abnormal l o a d i n g o f t h e a r t i c u l a r c a r t i l a g e o f t h e p a t e l l o f e m o r a l j o i n t o r abnormal s t r e s s t o t h e m e d i a l s o f t t i s s u e s t h e r e may be t r u e c h o n d r o m a l a c i a p a t e l l a e (wh i c h wou l d be d e t e r m i n e d by a r t h r o s c o p i c i n v e s t i g a t i o n ) , r e c u r r e n t s u b l u x a t i o n o r d i s l o c a t i o n o f t h e p a t e l l a and o t h e r c o n d i t i o n s w h i c h wou l d a t f i r s t r e s emb l e PFPS u n t i l t h e knee has been more t h o r o u g h l y e xam ined , such as O s g o o d - S c h l a t t e r ' s syndrome, q u a d r i c e p s t e n d i n i t i s , i n f r a p a t e l l a r t endon b u r s i t i s , pes a n s e r i n e b u r s i t i s , g e n e r a l i z e d s y n o v i t i s , f a t pad syndrome ( J ames , 1979 , F i c a t & H u n g e r f o r d , 1 9 7 7 ) . T h e r e f o r e , i n a n a l y z i n g t h e i n d i v i d u a l r e s u l t s i t i s o n l y p o s s i b l e t o make i n f e r e n c e s f r om t h e d a t a t h a t has been c o l l e c t e d , and where t h e EMG r e s u l t s , t h e mus c l e s t r e n g t h v a l u e s and t h e c l i n i c a l f e a t u r e s a g r e e , k e e p i n g i n m ind t h e s m a l l number o f s u b j e c t s i n t h e c o n t r o l g roup and t h e v a r i a b i l i t y o f t h a t g r o u p . - 58 - a . 6 _ 0 10 28 30 40 50 60 70 80 90 100 % CYCLE Figure 16 S u b j e c t S C . The ensemb le a v e r a g e s ( c r o s s e d l i n e ) o f t h e v a s t u s m e d i a l i s ( VM) , r e c t u s f e m o r i s (RF) and t h e v a s t u s l a t e r a l i s (VL ) o f t h i s s u b j e c t a r e compared t o t h e mean m u s c l e p a t t e r n s o f t h e c o n t r o l g r oup ( s o l i d l i n e ) + one s t a n d a r d d e v i a t i o n ( d o t t e d l i n e ) . H e e l - s t r i k e i s a t 0 and 100% o f t h e g a i t c y c l e , w h i l e t o e - o f f i s i n d i c a t e d by * . - 59 - As can be seen i n F i g u r e 16 , t h e a c t i v i t y l e v e l o f a l l t h r e e o f t h e q u a d r i c e p s m u s c l e s f o r S u b j e c t SC i s l e s s t h a n t h e a v e r age EMG o f t h e c o n t r o l g r o u p , and i n p a r t i c u l a r t h e v a s t u s m e d i a l i s i s o u t s i d e o f one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean d u r i n g e a r l y s t a n c e . A t t h i s p o i n t i n t h e g a i t c y c l e t h e knee i s f l e x i n g t o a b s o r b t h e f o r c e s o f f o o t c o n t a c t w h i l e t h e q u a d r i c e p s a r e w o r k i n g e c c e n t r i c a l l y t o c o n t r o l knee f l e x i o n ( W i n t e r , 1 9 8 3 ) . The r e was a l s o l e s s EMG a c t i v i t y i n t h e r e c t u s f e m o r i s o f S u b j e c t SC d u r i n g sw i ng pha s e , when i t i s t h o u g h t t o be w o r k i n g as a h i p f l e x o r ( E l l i o t t and B l a n k s b y , 1 9 7 9 ) . T h i s s u b j e c t ' s s t r e n g t h t e s t s r e v e a l e d t h a t h e r r i g h t q u a d r i c e p s were weake r t h a n t h e mean o f t h e c o n t r o l g roup b o t h e c c e n t r i c a l l y and c o n c e n t r i c a l l y ( T a b l e I V , T a b l e X I ) . Her h a m s t r i n g s / q u a d r i c e p s r a t i o (H/Q r a t i o ) was 1.23 c o n c e n t r i c a l l y and .95 e c c e n t r i c a l l y w h i c h i n d i c a t e s t h a t c o n c e n t r i c a l l y h e r h a m s t r i n g s were s t r o n g e r t h an h e r q u a d r i c e p s and n e a r l y t h e same s t r e n g t h e c c e n t r i c a l l y . The c o n c e n t r i c r a t i o i s o u t s i d e o f t h e r ange ( . 43 - .90) r e p o r t e d by Nosse ( 1 9 8 2 ) . Compar ing t h i s s u b j e c t ' s EMG p a t t e r n s o f t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s , t h e r e s u l t s i n d i c a t e d a n o t a b l e d i f f e r e n c e between t h e i r a c t i v i t y l e v e l s d u r i n g s t a n c e . As t h e q u a d r i c e p s work f i r s t e c c e n t r i c a l l y d u r i n g s t a n c e and t hen c o n c e n t r i c a l l y ( W i n t e r , 1983) i t may be t h a t t h e l o w e r peak EMG a m p l i t u d e o f t h e v a s t u s m e d i a l i s d u r i n g t h e r u n n i n g c y c l e i s r e f l e c t e d i n t h e r e d u c e d peak t o r q u e v a l u e s o f t h e q u a d r i c e p s f r om t h e s t r e n g t h t e s t . In t h i s c a s e i t may be t h a t t h e v a s t u s m e d i a l i s was no t a b l e t o b a l a n c e t h e l a t e r a l p u l l o f t h e v a s t u s l a t e r a l i s . - 60 - T h i s s u b j e c t had genu va l gum and a Q - ang l e o f 15° w h i c h a c c o r d i n g t o LeVeau & B e r n h a r d t (1984) enhances t h e t endency t o l a t e r a l t r a c k i n g o f t h e p a t e l l a . Her r e a r f o o t and f o r e f o o t v a r u s a l i g n m e n t wou l d be c o n s i d e r e d mode ra te ( T a u n t o n , e t a l . 1985) and a c o n t r i b u t i n g f a c t o r t owa rd s compensa to r y p r o n a t i o n o f h e r f o o t (James e t a l . 1 9 7 8 ) . She had e x p e r i e n c e d m e d i a l knee p a i n f o r s i x t o seven y e a r s and r e p o r t e d t h a t i t was p r e s e n t w i t h r u n n i n g . He r m e d i a l knee p a i n may be due t o e a r l i e r t h an normal c o n t a c t o f t h e odd f a c e t w i t h t h e m e d i a l f e m o r a l c o n d y l e as a r e s u l t o f l a t e r a l t r a c k i n g o f t h e p a t e l l a ( K e s s l e r and H e r t l i n g , 1 9 8 3 ) , o r due t o t h e m e d i a l s o f t t i s s u e s b e i n g s t r e t c h e d and s t r a i n e d l e a d i n g t o i n f l a m m a t i o n and p a i n ( L e V e a u , & B e r n h a r d t , 1 9 8 4 ) . - 61 - 0 . 6 ^ % CYCLE Figure 17 S u b j e c t HB. As i n F i g u r e 1 6 , t h e c r o s s e d l i n e r e p r e s e n t s t h e ensemb l e a v e r a g e o f t h e v a s t u s m e d i a l i s , r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s f o r t h i s s u b j e c t , compared t o t h e mean m u s c l e a c t i v i t y o f t h e c o n t r o l g r oup ( s o l i d l i n e ) + one s t a n d a r d d e v i a t i o n ( d o t t e d l i n e ) . - 62 - F i g u r e 17 showed t h a t t h e l e v e l s o f mus c l e a c t i v i t y o f t h e t h r e e q u a d r i c e p s m u s c l e s f r om S u b j e c t HB were l o w e r t h a n t h e means o f t h e c o n t r o l g r o u p . The r e s u l t s a l s o r e v e a l e d t h a t a l t h o u g h t h e p h a s i n g o f t h e p a t t e r n s was s i m i l a r , t h e peak EMG a m p l i t u d e s o f t h e v a s t u s m e d i a l i s d u r i n g s t a n c e and r e c t u s f e m o r i s d u r i n g sw i ng phase were l e s s t h a n one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean. T h i s s u b j e c t ' s peak t o r q u e v a l u e s f r om t h e s t r e n g t h t e s t were w i t h i n +_ one s t a n d a r d d e v i a t i o n o f t h e mean o f t h e c o n t r o l g roup e x c e p t f o r e c c e n t r i c q u a d r i c e p s w h i c h was l e s s t h a n - one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean (84 N.m compared t o 170 N.m + 5 0 . 3 3 ) . I t may be t h a t , s i m i l a r t o S u b j e c t SC , t h e r e d u c e d EMG l e v e l o f t h e v a s t u s m e d i a l i s d u r i n g s t a n c e i s a s s o c i a t e d w i t h t h e low e c c e n t r i c peak t o r q u e v a l u e f o r t h e q u a d r i c e p s f r om t h e s t r e n g t h t e s t . The H/Q r a t i o s f r om t h i s s u b j e c t were c o n c e n t r i c .86 and e c c e n t r i c 1 . 4 , w h i c h r e v e a l e d t h a t e c c e n t r i c a l l y h e r h a m s t r i n g s were s t r o n g e r t h a n t h e q u a d r i c e p s . A l t h o u g h t h e r e have been no p u b l i s h e d s t u d i e s on t h e knee f l e x o r / e x t e n s o r s t r e n g t h r e l a t i o n s h i p e c c e n t r i c a l l y , t h e mean H/Q r a t i o f o r t h e c o n t r o l g roup i n t h i s s t u d y was .73 (+ . 2 5 3 ) . S u b j e c t HB r e p o r t e d t h a t she had e x p e r i e n c e d r i g h t m e d i a l knee p a i n f o r a t l e a s t f i v e y e a r s , w h i c h was s e v e r e enough t o s t o p h e r f r om r u n n i n g . She had genu v a l g um , a Q - ang l e o f 20°, mode ra te r e a r f o o t and f o r e f o o t v a r u s a l i g n m e n t and compensa t o r y o v e r p r o n a t i o n . Her h i g h e r t h a n normal Q - ang l e and t h e genu va lgum may have been c o n t r i b u t i n g t o l a t e r a l t r a c k i n g o f t h e p a t e l l a and as such she c o u l d be e x p e r i e n c i n g h e r p a i n f r om o v e r s t r e t c h i n g o f t h e m e d i a l s o f t t i s s u e s o r f r om e a r l i e r t h a n normal - 63 - c o n t a c t o f t h e odd f a c e t on t h e m e d i a l f emo r a l c o n d y l e . L i e b and P e r r y (1971) and B a s m a j i a n (1970) have r e p o r t e d t h a t t h e v a s t u s m e d i a l i s s h o u l d o f f s e t t h e l a t e r a l and s u p e r i o r p u l l o f t h e v a s t u s l a t e r a l i s , b u t i t a ppea r s t h a t i n t h i s c a s e and i n S u b j e c t SC t h e v a s t u s m e d i a l i s had l e s s a c t i v i t y d u r i n g e a r l y s t a n c e and may have a l l o w e d a g r e a t e r deg ree o f l a t e r a l p u l l by t h e v a s t u s l a t e r a l i s . LeVeau and Roge r s (1980) s u g g e s t t h a t a weakened v a s t u s m e d i a l i s i s n o t a b l e t o c o n t r i b u t e t o t h e m a i n t e n a n c e o f normal a l i g n m e n t o f t h e p a t e l l a i n t h e f emo r a l g r o o v e . T h e r e f o r e , a l e s s a c t i v e v a s t u s m e d i a l i s i n i t s e l f may c o n t r i b u t e t o l a t e r a l t r a c k i n g o f t h e p a t e l l a ( F o x , 1 9 7 5 ) . - 64 - 1 I I I T 1 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0 % CYCLE Figure 18 S u b j e c t EC . A c o m p a r i s o n o f t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s ( c r o s s e d l i n e ) t o t h e mean m u s c l e a c t i v i t y o f t h e c o n t r o l g r oup ( s o l i d l i n e ) +_ one s t a n d a r d d e v i a t i o n ( d o t t e d l i n e ) . O n l y t h e a c t i v i t y p a t t e r n s f o r t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s m u s c l e s have been p r e s e n t e d f o r S u b j e c t EC , a s no r e c o r d i n g was o b t a i n e d f o r r e c t u s f e m o r i s . I n t h i s c a s e , t h e a m p l i t u d e o f b o t h m u s c l e s was be l ow t h a t o f t h e c o n t r o l g r oup e x c e p t a t h e e l - s t r i k e f o r t h e v a s t u s m e d i a l i s . The peak a m p l i t u d e o f t h e v a s t u s l a t e r a l i s i n s t a n c e was l e s s t h a n - one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean. In f a c t b o t h t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s had n e a r l y t h e same peak - 65 - a m p l i t u d e d u r i n g s t a n c e f o r t h i s s u b j e c t , a l t h o u g h t h e peak a m p l i t u d e o f t h e v a s t u s m e d i a l i s was s l i g h t l y g r e a t e r . A l l o f t h e peak t o r q u e v a l u e s f r om t h e s t r e n g t h t e s t f o r S u b j e c t EC were l o w e r t h a n t h e c o n t r o l g r o u p ' s a v e r a g e s . Her H/Q r a t i o s were 1.17 c o n c e n t r i c a l l y and 1.14 e c c e n t r i c a l l y i n d i c a t i n g t h a t t h e h a m s t r i n g s and q u a d r i c e p s were n e a r l y t h e same s t r e n g t h a l t h o u g h t h e h a m s t r i n g s were s l i g h t l y s t r o n g e r . The l i t e r a t u r e on H/Q r a t i o s s u g g e s t s t h a t c o n c e n t r i c a l l y t h e r a t i o v a r i e s f r om .43 - . 9 0 , d epend i ng upon t h e a n g u l a r v e l o c i t y . S u b j e c t EC was r u n n i n g an a v e r age o f 40 km/week. She n o t e d knee p a i n t h r e e months p r i o r t o t h e d i a g n o s i s o f P FPS . She had genu va lgum w i t h a Q -ang l e o f 20°, h e r r e a r f o o t v a r u s a l i g n m e n t was 8° and f o r e f o o t v a r u s a l i g n m e n t was 10°, and she had compensa t o r y p r o n a t i o n . Her l e f t l e g was 1.2 cm s h o r t e r t h a n t h e r i g h t . T h i s s u b j e c t ' s a l i g n m e n t measures may have p r e d i s p o s e d h e r t o l a t e r a l t r a c k i n g o f t h e p a t e l l a . R a t h e r t h a n e x p e r i e n c i n g m e d i a l knee p a i n however , she r e p o r t e d l a t e r a l and i n f r a p a t e l l a r p a i n . Some o f t h i s p a i n c o u l d be r e l a t e d t o h i g h e r t h a n normal c o m p r e s s i o n f o r c e s t h r o u g h t h e l a t e r a l f a c e t due t o e x c e s s i v e t i g h t e n i n g o f t h e l a t e r a l r e t i n a c u l u m ( F i c a t and H u n g e r f o r d , 1 9 7 7 ) . However , t h e s u b j e c t s were no t examined p a r t i c u l a r l y f o r e x c e s s i v e t i g h t e n i n g o f t h e l a t e r a l s o f t t i s s u e s , so i t i s n o t p o s s i b l e t o c o m p l e t e l y s u b s t a n t i a t e t h e l o c a t i o n o f h e r p a i n . Some a u t h o r s ( M a r i a n i and C a r u s o , 1979; F o x , 1975) have b e l i e v e d t h a t q u a d r i c e p s weakness i n p a t e l l a r syndromes i s a t t r i b u t a b l e s o l e l y t o weakness o f t h e v a s t u s m e d i a l i s , however t h e EMG r e s u l t s f r om t h i s s u b j e c t - 66 - s u g g e s t h e r a c t i v i t y l e v e l s a r e n e a r l y t h e same between t h e v a s t u s m e d i a l i s and v a s t u s l a t e r a l i s . Indeed i t i s t h e v a s t u s l a t e r a l i s t h a t has a r e d u c e d a m p l i t u d e compared t o t h e c o n t r o l g roup and w h i c h may be r e l a t e d t o h e r d e c r e a s e d q u a d r i c e p s s t r e n g t h . The r e s u l t s o f a p i l o t s t u d y ( M a c l n t y r e and R o b e r t s o n , i n p r e s s ) showed t h a t t h e v a s t u s l a t e r a l i s had a peak a m p l i t u d e i n s t a n c e h i g h e r t h a n t h e v a s t u s m e d i a l i s , s i m i l a r t o t h e r e s u l t s o f t h e c o n t r o l g roup i n t h i s s t u d y . - 67 - 0 . 6 _ % C Y C L E Figure 19 S u b j e c t TR. A c o m p a r i s o n o f t h e ensemb le a v e r a g e s o f t h e v a s t u s m e d i a l i s , r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s t o t h e a v e r a g e m u s c l e p a t t e r n s o f t h e c o n t r o l g r o u p . The EMG r e c o r d s o f S u b j e c t TR showed r e d u c e d a c t i v i t y i n t h e v a s t u s l a t e r a l i s d u r i n g t h e shock a b s o r p t i o n phase o f e a r l y s t a n c e . A t t h e same t i m e t h e a c t i v i t y i n t h e v a s t u s m e d i a l i s was g r e a t e r t h a n t h e c o n t r o l - 68 - g r o u p ' s mean a c t i v i t y t h r o u g h o u t t h e g a i t c y c l e . In f a c t t h e peak a m p l i t u d e o f t h e v a s t u s m e d i a l i s was g r e a t e r t h a n t h a t o f t h e v a s t u s l a t e r a l i s f o r t h i s s u b j e c t . R e c t u s f e m o r i s a l s o had i n c r e a s e d EMG a m p l i t u d e f r om s t a n c e phase i n t o e a r l y sw i ng compared t o t h e c o n t r o l g r o u p , and may i n d i c a t e t h a t i t i s c o n t r i b u t i n g more t han u sua l t o q u a d r i c e p s a c t i v i t y . The peak t o r q u e v a l u e s o f a l l o f S u b j e c t T R ' s s t r e n g t h t e s t s were l e s s t h a n one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean. Her H/Q r a t i o s were c o n c e n t r i c .85 and e c c e n t r i c . 6 . T h i s s u b j e c t had c o m p l a i n e d o f r i g h t m e d i a l knee p a i n f o r two y e a r s . She r e p o r t e d t h a t t h e p a i n had c a u s e d h e r t o s t o p r u n n i n g . She had genu va l gum, p l u s r e c u r v a t u m , w i t h a Q - ang l e o f 18°. She o v e r p r o n a t e d and had what i s c o n s i d e r e d t o be modera te v a r u s a l i g n m e n t o f h e r r i g h t f o o t . Her a l i g n m e n t may have been c o n t r i b u t i n g t o l a t e r a l t r a c k i n g o f t h e p a t e l l a , howeve r , i n t h i s c a s e t h e v a s t u s m e d i a l i s was more a c t i v e d u r i n g s t a n c e t h a t t h e v a s t u s l a t e r a l i s . - 69 - 0 . 6 ^ 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0 % C Y C L E Figure 20 S u b j e c t RW Ensemb le a v e r a g e s o f t h e t h r e e q u a d r i c e p s - t h e v a s t u s m e d i a l i s , r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s compared t o t h e c o n t r o l g r o u p . As can be seen i n F i g u r e 20, t h e EMG p a t t e r n s o f S u b j e c t RW f o l l o w e d t h e p a t t e r n s o f t h e c o n t r o l g r o u p . However , t h e peak a m p l i t u d e o f t h e v a s t u s l a t e r a l i s was l e s s t h a n one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l - 70 - g r o u p ' s mean i n s t a n c e and r e c t u s f e m o r i s was j u s t l e s s t h a n - one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean d u r i n g s t a n c e and s w i n g . The s t r e n g t h t e s t s r e v e a l e d o n l y t h e c o n c e n t r i c q u a d r i c e p s t o r q u e t o be weake r t h a n t h e c o n t r o l g r o u p ' s mean peak t o r q u e s . Her H/Q r a t i o s were c o n c e n t r i c 1.36 and e c c e n t r i c .9 i n d i c a t i n g t h a t h e r h a m s t r i n g s were s t r o n g e r c o n c e n t r i c a l l y t h a n h e r q u a d r i c e p s and t h a t t h e r e was l i t t l e d i f f e r e n c e i n t h e i r e c c e n t r i c peak t o r q u e s . T h i s s u b j e c t had s u f f e r e d f r om m e d i a l and r e t r o p a t e l l a r p a i n f o r two t o t h r e e y e a r s . The p a i n was p r e s e n t w h i l e she was r u n n i n g . She had genu varum w i t h a Q - ang l e o f 20° and m i l d v a r u s a l i g n m e n t o f h e r r i g h t f o o t , w i t h c ompensa t o r y p r o n a t i o n . James (1979) has r e p o r t e d a sequence o f m a l a l i g n m e n t f e a t u r e s t h a t he b e l i e v e s c o n t r i b u t e s t o an i n c r e a s e d Q - ang l e and l a t e r a l t r a c k i n g o f t h e p a t e l l a . He has f o u n d t h a t genu varum may accompany f emo r a l neck a n t e v e r s i o n , and t h a t i n an a t t e m p t t o p l a c e t h e f o o t s t r a i g h t ahead r a t h e r t h a n i n - t o e i n g , t h e p a t i e n t e x t e r n a l l y r o t a t e s t h e t i b i a w h i c h t h en i n c r e a s e s t h e Q - a n g l e . A l t h o u g h a n t e v e r s i o n / r e t r o v e r s i o n a t t h e h i p has n o t been e v a l u a t e d , J ames ' d e s c r i p t i o n o f ' m i s e r a b l e m a l a l i g n m e n t ' may a p p l y t o t h i s p a t i e n t . As i n S u b j e c t s EC and TR, t h e EMG r e c o r d s s u g g e s t t h a t t h e v a s t u s l a t e r a l i s i s n o t as a c t i v e as t h e v a s t u s m e d i a l i s d u r i n g s t a n c e p h a s e , and i n t h i s c a s e t h a t r e c t u s f e m o r i s i s l e s s a c t i v e t h a n t h e c o n t r o l g r o u p ' s mean a c t i v i t y . - 71 - 4 0 5 0 6 0 % C Y C L E ! 0 0 Figure 21 S u b j e c t S S . The EMG p r o f i l e s o f t h e v a s t u s m e d i a l i s , r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s s u p e r i m p o s e d on t h e g r a n d ensemb le a v e r a g e s o f t h e c o n t r o l g r o u p . The m u s c l e a c t i v a t i o n p a t t e r n s o f S u b j e c t SS were a l l l o w e r t h a n t h e c o n t r o l g r o u p ' s a v e r a g e p a t t e r n . The v a s t u s l a t e r a l i s was l e s s t h a n - one s t a n d a r d d e v i a t i o n d u r i n g s t a n c e and r e c t u s f e m o r i s was a l s o l o w e r t h a n one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean i n s w i n g p h a s e . - 72 - Not o n l y was t h e a m p l i t u d e l e s s , b u t i n t h i s c a s e r e c t u s f e m o r i s a l s o d e v i a t e d f r om i t s u s ua l p a t t e r n o f a c t i v i t y ( E l l i o t t and B l a n k s b y , 1979; M a c l n t y r e and R o b e r t s o n , i n p r e s s ) because o f t h e absence o f t h e s e cond c u r v e d u r i n g s w i n g . The s t r e n g t h t e s t s f o r t h i s s u b j e c t were a l l n e a r t o t h e a v e r a g e o f t h e c o n t r o l g r o u p , e x c e p t f o r e c c e n t r i c q u a d r i c e p s t o r q u e w h i c h was above one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean. Her H/Q r a t i o s were .84 c o n c e n t r i c a l l y and .52 e c c e n t r i c a l l y , i n d i c a t i n g t h a t h e r q u a d r i c e p s were s t r o n g e r t h a n t h e h a m s t r i n g s . S u b j e c t SS r e p o r t e d t h a t she had s u f f e r e d f r om m e d i a l and r e t r o p a t e l l a r p a i n f o r s i x y e a r s . She had genu va rum, w i t h a Q - ang l e o f 17° and h e r l e f t l e g was one c e n t i m e t e r s h o r t e r t h a n t h e r i g h t . Her r e a r f o o t and f o r e f o o t v a r u s a l i g n m e n t was c o n s i d e r e d m o d e r a t e , c o n t r i b u t i n g t o o v e r p r o n a t i o n o f h e r f o o t . S i m i l a r t o S u b j e c t RW, t h i s s u b j e c t ' s a l i g n m e n t may f i t J a m e s ' ( 1979) d e s c r i p t i o n o f ' m i s e r a b l e m a l a l i g n m e n t ' , w h i c h may have c o n t r i b u t e d t o l a t e r a l t r a c k i n g o f t h e p a t e l l a . Even though t h i s s u b j e c t ' s s t r e n g t h t e s t s were n e a r t o t h e c o n t r o l g r o u p ' s a v e r a g e o r a bove , i t wou l d appea r t h a t t h e v a s t u s l a t e r a l i s was l e s s a c t i v e d u r i n g t h e s t a n c e phase o f r u n n i n g . S i m i l a r l y , r e c t u s f e m o r i s d i d n o t show t h e s e cond b u r s t o f a c t i v i t y i n sw ing p h a s e . T h i s s u b j e c t ' s r e s u l t s i n d i c a t e t h e v a l u e o f d e t e r m i n i n g an EMG p e r c e n t u t i l i z a t i o n v a l u e . R i c h a r d s e t a l . (1985) have d e s c r i b e d t h i s v a l u e as t h e peak EMG a m p l i t u d e d u r i n g g a i t / p e a k EMG a m p l i t u d e d u r i n g a max imal v o l u n t a r y c o n t r a c t i o n x 100%. A l t h o u g h t h i s s t u d y d i d n o t l e n d i t s e l f t o o b t a i n i n g - 73 - t h i s v a l u e due t o t h e l o g i s t i c s o f equ i pmen t l o c a t i o n , i t wou l d have been a u s e f u l i n d i c a t o r o f t h e p e r c e n t o f a c t i v a t i o n o f a m u s c l e d u r i n g g a i t . F o u r o u t o f e i g h t o f t h e e x p e r i m e n t a l s u b j e c t s had EMG a m p l i t u d e s f r om t h e v a s t u s l a t e r a l i s l e s s t h an - one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean d u r i n g t h e s t a n c e phase o f r u n n i n g , w h i l e o n l y two o u t o f e l e v e n o f t h e s u b j e c t s i n t h e c o n t r o l g roup were l e s s t h a n - one s t a n d a r d d e v i a t i o n ( T a b l e V I I ) . A l t h o u g h t h e p r e s e n t s u b j e c t numbers were s m a l l t h i s may i n d i c a t e a need f o r f u r t h e r s t u d y t o d e t e r m i n e i f t h e r e wou l d be a s i g n i f i c a n t d i f f e r e n c e between t h e g roups when c o m p a r i n g t h e peak a m p l i t u d e s o f t h e v a s t u s l a t e r a l i s d u r i n g s t a n c e , i f s u b j e c t numbers were g r e a t e r . F u r t h e r m o r e , a s t a t i s t i c a l a n a l y s i s w i t h a t - t e s t i n d i c a t e d t h a t i f t h e v a s t u s l a t e r a l i s had been t h e o n l y mus c l e t e s t e d t h e r e wou l d have been a s i g n i f i c a n t d i f f e r e n c e between t h e g roups when c ompa r i n g t h e peak EMG a m p l i t u d e s . However , t h e c l i n i c a l i n f o r m a t i o n f o r each o f t h e f o u r s u b j e c t s w i t h a r e d u c e d v a s t u s l a t e r a l i s EMG a m p l i t u d e was i n c o n s i s t e n t and d i f f i c u l t t o e x p l a i n i n r e l a t i o n t o t h e mus c l e a c t i v i t y . Th r ee o f t h e s u b j e c t s had m e d i a l knee p a i n , w h i l e one had l a t e r a l knee p a i n . Two s u b j e c t s had genu va lgum and two had genu va rum, a l t h o u g h as LeVeau and B e r n h a r d t (1984) and James (1979) have s u g g e s t e d , i t i s p o s s i b l e t o have l a t e r a l t r a c k i n g o f t h e p a t e l l a as a r e s u l t o f each t y p e o f knee a l i g n m e n t and t h e e f f e c t s i t has on o t h e r a s p e c t s o f t h e l o w e r e x t r e m i t y . A d d i t i o n a l l y , t h e mus c l e s t r e n g t h r e s u l t s v a r i e d f r om one s u b j e c t w i t h v a l u e s n e a r t o t h e c o n t r o l g r o u p ' s mean e x c e p t f o r e c c e n t r i c q u a d r i c e p s wh i c h was above one s t a n d a r d d e v i a t i o n , t o one s u b j e c t who had v a l u e s a l l - 74 - l e s s t h an - one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean. In d i s c u s s i n g q u a d r i c e p s weakne s s , t h e l i t e r a t u r e has emphas i z ed t h a t t h e v a s t u s m e d i a l i s i s t h e mus c l e t h a t i s most o f t e n weake r ( H u g h s t o n , 1968 , Fox 1975 , M a r i a n i & C a r u s o , 1979 , LeVeau & R o g e r s , 1980) b u t i t wou l d a ppea r f r om t h e r e s u l t s o f t h i s s t u d y t h a t weakness o f t h e v a s t u s l a t e r a l i s may a l s o o c c u r i n PFPS and f u r t h e r i n v e s t i g a t i o n wou l d be w a r r a n t e d . - 75 - 0 . 6 _ 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0 % C Y C L E Figure 22 S u b j e c t J H . A c o m p a r i s o n o f t h i s s u b j e c t ' s ensemb le a v e r a g e s o f t h e v a s t u s m e d i a l i s , r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s t o t h e a v e r a g e p a t t e r n s o f t h e c o n t r o l g r o u p . The EMG p r o f i l e s f o r t h e v a s t u s l a t e r a l i s and t h e v a s t u s m e d i a l i s f r om t h i s s u b j e c t had a s i m i l a r p a t t e r n t o t h e c o n t r o l g r o u p ' s a v e r a g e p a t t e r n , a l t h o u g h t h e peak a m p l i t u d e s we re s l i g h t l y l a t e r and l o w e r d u r i n g s t a n c e - 76 - t h a n t h e c o n t r o l g r o u p . The peak a m p l i t u d e f o r r e c t u s f e m o r i s d u r i n g s t a n c e was above one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean, b u t d u r i n g sw i ng phase t h e r e was an absence o f t h e s e cond c u r v e . T h i s s u b j e c t ' s s t r e n g t h v a l u e s were a l l n e a r t o t h e c o n t r o l g r o u p ' s a v e r a g e s and h e r H/Q r a t i o s were c o n c e n t r i c .7 and e c c e n t r i c . 6 4 . She r e p o r t e d i n f r a p a t e l l a r p a i n o f two y e a r s d u r a t i o n and a l t h o u g h she e x p e r i e n c e d t h e p a i n w h i l e r u n n i n g , she had no t s t o p p e d . Her Q - ang l e was 20°, she had genu va rum, m i l d v a r u s a l i g n m e n t a t h e r f o o t and compensa t o r y p r o n a t i o n . From t h e EMG r e c o r d s , t h e r e appea r ed t o be l e s s r e c r u i t m e n t o f r e c t u s f e m o r i s d u r i n g sw i ng phase f o r t h i s s u b j e c t , b u t a g r e a t e r l e v e l o f a c t i v i t y d u r i n g s t a n c e p h a s e . O t h e r w i s e h e r mus c l e s t r e n g t h and EMG a c t i v i t y l e v e l s were n e a r t o t h e c o n t r o l g r o u p ' s mean. F i v e o u t o f seven o f t h e e x p e r i m e n t a l s u b j e c t s had an EMG a m p l i t u d e l e s s t h a n - one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean d u r i n g t h e sw ing phase o f r e c t u s f e m o r i s , w h i l e two o u t o f e l e v e n o f t h e c o n t r o l g r o u p ' s s u b j e c t s f e l l o u t s i d e o f - one s t a n d a r d d e v i a t i o n ( T a b l e V I I ) . A l t h o u g h t h i s s t u d y has no t c o n s i d e r e d t h e r o l e o f r e c t u s f e m o r i s as a h i p f l e x o r d u r i n g t h e sw i ng phase o f r u n n i n g i t w o u l d a ppea r t h a t t h i s wou l d be a w o r t h w h i l e p r o j e c t t o p u r s u e . - 77 - 0 . 6 _ % C Y C L E Figure 23 S u b j e c t J G . The ensemb l e a v e r a g e s o f t h e v a s t u s m e d i a l i s , r e c t u s f e m o r i s and t h e v a s t u s l a t e r a l i s compared t o t h e c o n t r o l g r o u p ' s a v e r a g e m u s c l e a c t i v i t y . T h i s s u b j e c t ' s EMG p a t t e r n s f o l l o w e d t h e p r o f i l e s o f t h e c o n t r o l g r oup b u t we re s l i g h t l y l o w e r i n a m p l i t u d e , e x c e p t f o r r e c t u s f e m o r i s d u r i n g s t a n c e . In t h i s c a s e t h e peak a m p l i t u d e o f r e c t u s f e m o r i s was above one s t a n d a r d d e v i a t i o n o f t h e c o n t r o l g r o u p ' s mean. - 78 - Her mus c l e s t r e n g t h v a l u e s were a l l l e s s t h an t h e c o n t r o l g r o u p ' s means and i n f a c t , t h e c o n c e n t r i c q u a d r i c e p s and h a m s t r i n g s were o u t s i d e o f - one s t a n d a r d d e v i a t i o n . Her H/Q r a t i o s were c o n c e n t r i c 1.09 and e c c e n t r i c .70 w h i c h i n d i c a t e d t h a t h e r c o n c e n t r i c q u a d r i c e p s and h a m s t r i n g s were n e a r l y t h e same s t r e n g t h , w h i l e d u r i n g e c c e n t r i c t e s t i n g h e r q u a d r i c e p s were s t r o n g e r t h a n t h e h a m s t r i n g s . She had n o t e d m e d i a l and r e t r o p a t e l l a r p a i n f o r s i x mon th s . Her Q - ang l e was 19°, w i t h genu v a l g um , m i l d v a r u s a l i g n m e n t o f h e r f o o t and compensa to r y p r o n a t i o n . As i n S u b j e c t SS t h e a p p a r e n t i n c o n g r u e n c y between t h i s s u b j e c t ' s d e c r e a s e d s t r e n g t h v a l u e s b u t EMG p a t t e r n s s i m i l a r t o t h e c o n t r o l g r o u p ' s a v e r age p a t t e r n s may have been e x p l a i n e d by a p e r c e n t EMG u t i l i z a t i o n v a l u e . I t may be t h a t a l t h o u g h h e r m u s c l e s a r e weake r she was r e c r u i t i n g a t a h i g h p e r c e n t a g e d u r i n g r u n n i n g . - 79 - Conclusion A l t h o u g h t h e r e s u l t s o f t h e g roup EMG p a t t e r n s i n d i c a t e d t h a t t h e r e was no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between t h e two g r o u p s , a n a l y z i n g i n d i v i d u a l EMG p a t t e r n s c o u l d p r o v e t o be v a l u a b l e i n d i r e c t i n g a r e h a b i l i t a t i o n p rogram f o r t h e r u n n e r . I f t h e r e was a l a r g e bank o f normal d a t a w i t h w h i c h t o compare , t h e mus c l e a c t i v i t y o f a p a t i e n t w i t h PFPS o r any o t h e r c l i n i c a l c o n d i t i o n c o u l d be a n a l y z e d d u r i n g f u n c t i o n a l a c t i v i t y and t h o s e EMG p a t t e r n s t h a t d e v i a t e d f r om t h e normal d i s t r i b u t i o n c o u l d be t h e f o c u s o f a m u s c l e r e - e d u c a t i o n p rogram i n r e g a r d t o s t r e n g t h e n i n g , e l e c t r i c a l s t i m u l a t i o n and g a i t t r a i n i n g . The r e s u l t s o f t h i s s t u d y s u g g e s t t h a t t h e r e may n o t be a p a r t i c u l a r p a t t e r n o f m u s c l e a c t i v i t y t h a t i s common t o a l l p a t i e n t s w i t h P FPS . T h i s l a c k o f a common f i n d i n g may be due t o t h e many p o s s i b l e i n t e r a c t i o n s o f m a l a l i g n m e n t f e a t u r e s and e t i o l o g y t h a t t h e c l i n i c i a n may f i n d i n each i n d i v i d u a l . However , t h e f i n d i n g s must be c o n s i d e r e d c a u t i o u s l y due t o t h e sma l l number o f s u b j e c t s i n t h i s s t u d y . T h i s s t u d y has a t t e m p t e d t o compare c l i n i c a l f e a t u r e s and EMG a c t i v i t y d u r i n g r u n n i n g b u t i t i s n e c e s s a r y t o r e c o g n i z e t h a t t h e r e a r e some l i m i t a t i o n s i n t h i s a n a l y s i s . As t h e knee i s f l e x i n g d u r i n g e a r l y s t a n c e and a b s o r b i n g t h e f o r c e s o f t h e f o o t h i t t i n g t h e g r o u n d , n o t o n l y i s t h e r e e c c e n t r i c a c t i v i t y o f t h e q u a d r i c e p s t o c o n t r o l knee f l e x i o n ( W i n t e r , 1 9 8 3 ) , b u t a c c o r d i n g t o E l l i o t t and B l a n k s b y (1979) t h e r e i s a s i m u l t a n e o u s c o n t r a c t i o n o f t h e h a m s t r i n g s g r o u p . D u r i n g sw i ng phase t h e r e i s a l s o knee f l e x o r a c t i v i t y . C o n s i d e r i n g t h a t f i v e o u t o f e i g h t o f t h e e x p e r i m e n t a l s u b j e c t s had H/Q r a t i o s g r e a t e r t h a n one , i n d i c a t i n g t h a t - 80 - t h e h a m s t r i n g s were s t r o n g e r t h a n t h e q u a d r i c e p s , i t wou l d have been o f b e n e f i t t o s t u d y t h e a c t i v i t y o f b o t h t h e q u a d r i c e p s and t h e h a m s t r i n g s e l e c t r o m y o g r a p h i c a l l y d u r i n g r u n n i n g . A d d i t i o n a l l y , a c o m p a r i s o n o f t h e m u s c l e a c t i v i t y p a t t e r n s o f t h e e x p e r i m e n t a l g roup r e v e a l e d t h a t t h e r e was more o r l e s s a c t i v i t y t h a n t h e c o n t r o l g r o u p ' s mean EMG p r o f i l e , b u t t h i s d i d n o t i n d i c a t e what deg ree o r p e r c e n t o f m u s c l e a c t i v i t y was i n v o l v e d f o r each s u b j e c t . As s u g g e s t e d i n t h e d i s c u s s i o n , a p e r c e n t EMG u t i l i z a t i o n v a l u e , w h i c h R i c h a r d s e t a l . (1985) have d e s c r i b e d and used may have a l l o w e d an e x p l a n a t i o n as t o why some s u b j e c t s had normal mus c l e s t r e n g t h d u r i n g t e s t i n g b u t d e c r e a s e d mus c l e a c t i v i t y f u n c t i o n a l l y and c o n v e r s e l y , d e c r e a s e d m u s c l e s t r e n g t h b u t EMG a c t i v i t y d u r i n g r u n n i n g w h i c h c l o s e l y a p p r o x i m a t e d t h a t o f t h e c o n t r o l g r o u p . I t wou l d a l s o add i n f o r m a t i o n i n r e l a t i n g t h e i n d i v i d u a l EMG p r o f i l e s t o t h e c o n t r o l g r o u p ' s mean EMG p a t t e r n . A l t h o u g h we r e c o g n i z e t h e s e l i m i t a t i o n s , each a t t e m p t t o r e l a t e c l i n i c a l f e a t u r e s w i t h f u n c t i o n a l mus c l e a c t i v i t y makes a c o n t r i b u t i o n t o t h e u n d e r s t a n d i n g o f t h i s r e l a t i o n s h i p and p r o v i d e s a b a s i s f o r t h e n e x t s t u d y . - 81 - APPENDIX 4 REVIEW OF THE LITERATURE OVERVIEW OF THE CHAPTER The f i r s t p a r t o f t h i s c h a p t e r e n t a i l s a r e v i e w o f t h e l i t e r a t u r e on p a t e l l o f e m o r a l p a i n synd rome . The anatomy and b i o m e c h a n i c s o f t h e p a t e l l o f e m o r a l j o i n t a r e a d d r e s s e d b e f o r e t h e d i s c u s s i o n r e g a r d i n g t h e c l i n i c a l f e a t u r e s and t h e more comp lex i s s u e o f t h e e t i o l o g y o f p a t e l l o f e m o r a l p a i n . The s e cond and t h i r d m a j o r p a r t s o f t h e l i t e r a t u r e r e v i e w c o n c e r n t h e a n a l y s i s o f mus c l e a c t i v i t y a t t h e knee d u r i n g r u n n i n g . A d i s c u s s i o n o f e l e c t r o m y o g r a p h y , i n p a r t i c u l a r r e p o r t s o f s t u d i e s on t h e knee m u s c l e s d u r i n g r u n n i n g , l e a d s i n t o a r e v i e w o f o t h e r t y p e s o f k i n e m a t i c a n a l y s e s o f r u n n i n g . F i n a l l y , a r e v i e w o f t h e l i t e r a t u r e c o n c e r n i n g t h e r e l a t i v e l y new c o n c e p t o f i s o k i n e t i c mus c l e a c t i v i t y and s t r e n g t h t e s t i n g i s p r e s e n t e d . - 82 - PATELLOFEMORAL PAIN SYNDROME Introduction A c c o r d i n g t o Ma lek and Mang ine ( 1 9 8 1 ) , t h e f i r s t d e s c r i p t i o n o f d e g e n e r a t i v e changes o f t h e p a t e l l o f e m o r a l j o i n t was r e p o r t e d i n t h e e a r l y 1 9 0 0 ' s . S i n c e t h e n , t h ey r e p o r t t h a t as many as 400 a r t i c l e s have been w r i t t e n a t t e m p t i n g t o e x p l a i n t h e p a t e l l a r s ynd romes . These same a u t h o r s s u g g e s t t h a t p a t e l l o f e m o r a l p a i n syndrome (PFPS) i s t h e m a j o r c au se o f knee p a i n i n most s p o r t s m e d i c i n e c l i n i c s i n t h e U . S . C l emen t e t a l . ( 1 9 8 1 ) , i n a two y e a r r e t r o s p e c t i v e s u r v e y c o n d u c t e d i n Canada , f o u n d t h a t amongst t h e i r p a t i e n t s t h e knee was t h e most commonly i n j u r e d s i t e and PFPS t h e most common i n j u r y . Anatomy of the Patellofemormal Joint The p a t e l l a , w h i c h i s t h e l a r g e s t s e samo i d bone i n t h e body , i s i n t e r p o s e d i n t h e q u a d r i c e p s t endon (Ma lek and Mang i n e , 1 9 8 1 ) . D u r i n g f l e x i o n and e x t e n s i o n o f t h e knee t h e p a t e l l a s h o u l d g l i d e i n l i n e w i t h t h e l o n g a x i s o f t h e f emu r . In o r d e r t o do t h i s , s t a b i l i z a t i o n o f t h e p a t e l l a i s p r o v i d e d by a c t i v e and p a s s i v e e l e m e n t s o f t h e e x t e n s o r mechan ism p l u s t o r s i o n a l and a n g u l a r a l i g n m e n t o f t h e femur and t i b i a ( J ames , 1 9 7 9 ) . The p a s s i v e s t a b i l i z e r s i n c l u d e t h e j o i n t c a p s u l e w h i c h e n c l o s e s b o t h t h e t i b i o f e m o r a l j o i n t and t h e p a t e l l o f e m o r a l j o i n t , t h e m e d i a l and l a t e r a l r e t i n a c u l a r e x p a n s i o n s , t h e m e d i a l and l a t e r a l p a t e l l o f e m o r a l l i g a m e n t s , and t h e p a t e l l a r t endon ( F i c a t and H u n g e r f o r d , 1 9 7 7 ) . The l a t e r a l p a t e l l o f e m o r a l l i g a m e n t i s a p a r t o f t h e l a t e r a l r e t i n a c u l u m . The - 83 - deep l a y e r s o f t h e l a t e r a l r e t i n a c u l u m expand i n t o t h e r e t i n a c u l u m o f t h e v a s t u s l a t e r a l i s mus c l e and t h e i l i o t i b i a l t r a c t . F i c a t and H u n g e r f o r d (1977) s u g g e s t t h a t t h e l a t e r a l r e t i n a c u l u m i s n o r m a l l y t h i c k e r t h an t h e m e d i a l r e t i n a c u l u m , and because i t i s a l s o r e i n f o r c e d by t h e i l i o t i b i a l band and v a s t u s l a t e r a l i s , i t may a c c e n t u a t e t h e t endency t o l a t e r a l d i s p l a c e m e n t o f t h e p a t e l l a . The p a t e l l a r t e n d o n , w h i c h s t a b i l i z e s t h e p a t e l l a i n f e r i o r l y , l i m i t s t h e p r o x i m a l a s c e n t o f t h e p a t e l l a f r om t h e t i b i a and e s t a b l i s h e s t h e p o s i t i o n o f t h e p a t e l l a r e l a t i v e t o t h e f emo ra l c o n d y l e s . I t i s n o r m a l l y a l i g n e d a l o n g t h e l o n g a x i s o f t h e t i b i a b u t when i t s d i r e c t i o n o f p u l l i s s l i g h t l y l a t e r a l f r om p r o x i m a l t o d i s t a l , i t adds t o t h e t endency t o l a t e r a l d i s p l a c e m e n t o f t h e p a t e l l a ( F i c a t and H u n g e r f o r d , 1 9 7 7 ) . The bony c o n t o u r s o f t h e f emo r a l s u l c u s and t h e c o n f i g u r a t i o n o f t h e p a t e l l a a r e a l s o c o n s i d e r e d p a s s i v e o r s t a t i c s t a b i l i z e r s . The t r i a n g u l a r shaped p a t e l l a l i e s a n t e r i o r t o t h e t i b i o f e m o r a l j o i n t and i s a t t a c h e d p r o x i m a l l y t o t h e q u a d r i c e p s by t h e q u a d r i c e p s t e n d o n , and d i s t a l l y t o t h e t i b i a l t u b e r c l e by t h e p a t e l l a r t e n d o n . The p o s t e r i o r s u r f a c e i s c o v e r e d by a r t i c u l a r c a r t i l a g e o v e r 75% o f i t s s u r f a c e and i s d i v i d e d i n t o f i v e r e g i o n s - t h e s u p e r i o r , i n f e r i o r , m e d i a l , l a t e r a l and odd f a c e t s . A c e n t r a l v e r t i c a l r i d g e s e p e r a t e s t h e m e d i a l and l a t e r a l r e g i o n s ( James , 1 9 7 9 ) . The i n t e r c o n d y l a r g roove on t h e a n t e r i o r a s p e c t o f t h e d i s t a l f emur r e p r e s e n t s t h e f emo r a l a r t i c u l a r s u r f a c e . The c e n t r a l g r oove c o r r e s p o n d s t o t h e v e r t i c a l r i d g e on t h e p a t e l l a and d i v i d e s t h e f emo r a l s u r f a c e s i n t o m e d i a l and l a t e r a l . H y a l i n e c a r t i l a g e c o v e r s t h e a r t i c u l a r s u r f a c e . - 84 - Normal dep th o f t h e i n t e r c o n d y l a r g r oove and h e i g h t o f t h e l a t e r a l f emo r a l c o n d y l e b u t t r e s s t h e p a t e l l a a g a i n s t l a t e r a l d i s l o c a t i o n ( James , 1 9 7 9 ) . The dep th o f t h i s f emo r a l a r t i c u l a t i o n i s a l s o i m p o r t a n t i n t h e c ong ruen cy o f t h e p a t e l l o f e m o r a l j o i n t , as i s t h e shape o f t h e p a t e l l a . W i be rg (1941) has d e s c r i b e d s i x c o n f i g u r a t i o n s o f p a t e l l a e , each one c o n t r i b u t i n g d i f f e r e n t l y t o t h e c ong ruency o f t h e j o i n t . The p a t e l l o f e m o r a l j o i n t i s s u p p l i e d by t h e p o p l i t e a l a r t e r y w h i c h g i v e s b r an che s m e d i a l l y and l a t e r a l l y t h a t f o rm a c o l l a t e r a l c i r c u l a t i o n a t t h e knee ( A n d e r s o n , 1 9 8 3 ) . I n n e r v a t i o n t o t h e knee i s f r om t h e t h i r d l umba r t o t h e s e cond s a c r a l s egmen t s . The a n t e r o - m e d i a l and m e d i a l a s p e c t s a r e s u p p l i e d by t h e t h i r d l umba r segment , w h i c h a l s o s u p p l i e s t h e h i p . T h e r e f o r e , when a s s e s s i n g knee p a i n one must remember t h a t t h e l u m b o s a c r a l r e g i o n o r t h e h i p may r e f e r p a i n t o t h e knee ( K e s s l e r & H e r t l i n g , 1 9 8 3 ) . A l l f o u r o f t h e q u a d r i c e p s m u s c l e s a r e c o n s i d e r e d t o be a c t i v e s t a b i l i z e r s , w i t h t h e v a s t u s m e d i a l i s r e i n f o r c i n g t h e m e d i a l r e t i n a c u l u m and m e d i a l p a t e l l o f e m o r a l l i g a m e n t , and t h e v a s t u s l a t e r a l i s r e i n f o r c i n g t h e l a t e r a l s o f t t i s s u e s . However , t h e more d i s t a l segment o f t h e v a s t u s m e d i a l i s , c a l l e d v a s t u s m e d i a l i s o b l i q u e (VMO), i s t h o u g h t t o be t h e most i m p o r t a n t dynamic s t a b i l i z e r o f t h e p a t e l l a (Ma lek and Mang i n e , 1 9 8 1 ) . I t has been r e p o r t e d by L i e b and P e r r y (1971) t h a t t h e m a j o r f u n c t i o n o f VMO i n p a t e l l a r a l i g n m e n t i s t o o f f s e t t h e s u p e r i o r and l a t e r a l p u l l o f v a s t u s l a t e r a l i s . B a s m a j i a n (1970) and James (1979) have s u g g e s t e d t h a t VMO p r e v e n t s l a t e r a l d i s p l a c e m e n t o f t h e p a t e l l a due t o t h e o r i e n t a t i o n o f i t s f i b r e s i n t o t h e p a t e l l a a t an a n g l e o f a p p r o x i m a t e l y 50° t o t h e l o n g a x i s o f t h e f emu r . - 85 - A l t h o u g h i t a ppea r s t o be a s i g n i f i c a n t m u s c l e i n p a t e l l a r a l i g n m e n t and i n t h e f i n a l d eg r e e s o f knee e x t e n s i o n , i t i s i m p o r t a n t t o no t e t h a t VMO can n o t work a l o n e t o e x t e n d t h e knee ( L i e b and P e r r y , 1 9 7 1 ) . In f a c t , a l l o f t h e q u a d r i c e p s work t o g e t h e r t h r o u g h o u t t h e f u l l r ange o f knee e x t e n s i o n ( H a l l e n and L i n d a h l , 1 9 6 7 ) . The pes a n s e r i n e m u s c l e s ( s a r t o r i u s , g r a c i l i s and s e m i t e n d i n o s u s ) i n s e r t m e d i a l l y on t h e p r o x i m a l t i b i a , and a r e t h o u g h t t o a s s i s t i n a c t i v e s t a b i l i z a t i o n t h r o u g h an i n t e r n a l r o t a t o r y a c t i o n on t h e p r o x i m a l t i b i a ( P a u l o s e t a l . 1 9 8 0 ) . L a t e r a l l y , t h e b i c e p s f e m o r i s may a f f e c t e x t e r n a l r o t a t i o n o f t h e t i b i a t h r o u g h t h e p a r t o f i t s i n s e r t i o n o n t o t h e l a t e r a l a s p e c t o f t h e p r o x i m a l t i b i a ( C a i l l i e t , 1 9 7 3 ) . T o g e t h e r t h e s e m e d i a l and l a t e r a l i n s e r t i n g m u s c l e s c o n t r i b u t e t o t h e e x t e n s o r mechan ism a l i g n m e n t by c h a n g i n g t h e p o s i t i o n o f t h e t i b i a l t u b e r c l e and i t s r e l a t i o n s h i p t o t h e p a t e l l a and t h e f e m o r a l s u l c u s ( J ames , 1 9 7 9 ) . In summary, t h e s t a t i c and dynamic e l e m e n t s o f s t a b i l i z a t i o n must f u n c t i o n t o g e t h e r f o r normal p a t e l l o f e m o r a l m e c h a n i c s . Biomechanics of the Patellofemoral Joint One o f t h e m a j o r f u n c t i o n s o f t h e p a t e l l a i s t o i n c r e a s e t h e e x t e n s o r f o r c e o f t h e q u a d r i c e p s m u s c l e . I t does t h i s by i n c r e a s i n g t h e d i s t a n c e between t h e a x i s o f m o t i o n a t t h e f emo r a l c o n d y l e and t h e q u a d r i c e p s t e n d o n , t h e r e b y i n c r e a s i n g t h e e x t e n s o r moment a rm . F i c a t and H u n g e r f o r d (1977) r e p o r t t h a t t h r o u g h o u t t h e e n t i r e range o f m o t i o n o f t h e k n e e , t h e p a t e l l a i n c r e a s e s t h e f o r c e o f t h e q u a d r i c e p s by as much as 50%, depend i ng on t h e amount o f knee f l e x i o n . - 86 - A n o t h e r m a j o r f u n c t i o n o f t h e p a t e l l a i s t h a t i t c e n t r a l i z e s t h e d i v e r g e n t f o r c e s f r om t h e q u a d r i c e p s and d i s t r i b u t e s t h e s e f o r c e s t h r o u g h t h e p a t e l l a r t endon t o t h e t i b i a and t h r o u g h t h e a r t i c u l a r c a r t i l a g e o f t h e p a t e l l a t o t h e f e m u r . P a t e l l o f e m o r a l j o i n t r e a c t i o n f o r c e s , w i t h t h e s upe r impo sed l o a d o f a c t i v i t y p l u s t h e t o r q u e g e n e r a t e d by t h e q u a d r i c e p s , can become as h i g h as t h r e e t i m e s body w e i g h t w i t h s t a i r - c l i m b i n g and e i g h t t i m e s body w e i g h t i n s q u a t t i n g ( J ames , 1 9 7 9 ) . These h i g h l o a d s compress t h e a r t i c u l a r c a r t i l a g e between an a r e a o f p a t e l l o f e m o r a l c o n t a c t wh i c h James (1979) r e p o r t s i s n e v e r more t h a n abou t one t h i r d o f t h e p a t e l l a r a r t i c u l a r s u r f a c e a t any g i v e n r ange o f m o t i o n . The p a t e l l o f e m o r a l j o i n t r e a c t i o n f o r c e s a r e a l s o a f f e c t e d by t h e c o n f i g u r a t i o n o f t h e p a t e l l a . The p o r t i o n o f t h e a r t i c u l a r s u r f a c e t h a t shows t h e most v a r i a t i o n i s t h e m e d i a l f a c e t ( F i c a t and H u n g e r f o r d , 1 9 7 7 ) . When t h i s f a c e t i s s m a l l e r o r d i f f e r e n t l y s haped , t h e j o i n t r e a c t i o n f o r c e s a r e i n c r e a s e d w h i c h o v e r l o a d s t h e a r t i c u l a r c a r t i l a g e o f t h e m e d i a l f a c e t . However , a p p r o x i m a t e l y 65% o f t h e p o p u l a t i o n have n o r m a l l y shaped p a t e l l a e and t h e i r j o i n t r e a c t i o n f o r c e s a r e n o r m a l l y d i s t r i b u t e d o v e r t h e c o n t a c t s u r f a c e o f t h e p a t e l l a . ( J ames , 1 9 7 9 ) . Clinical Features P a t e l l o f e m o r a l p a i n syndrome (PFPS) i s d e s c r i b e d as a d i f f u s e , p o o r l y l o c a t e d p a i n a r ound t h e p a t e l l a w h i c h a r i s e s f r om abnormal t r a c k i n g o f t h e p a t e l l a (G rana e t a l . 1 9 8 4 ) . I t may be r e f e r r e d t o as p e r i p a t e l l a r syndrome, p a t e l l a r m a l a l i g n m e n t , p a t e l l o f e m o r a l a r t h r a l g i a , o r r u n n e r ' s - 87 - k n e e , however i t i s c l i n i c a l l y d i f f e r e n t i a t e d f r om c h o n d r o m a l a c i a p a t e l l a e i n t h a t c h o n d r o m a l a c i a i m p l i e s l e s i o n s o f t h e r e t r o a r t i c u l a r c a r t i l a g e upon a r t h r o s c o p i c i n v e s t i g a t i o n ( B e n t l e y and Dowd, 1 9 8 4 ) . I t has been r e p o r t e d t h a t PFPS a f f e c t s t e enage f e m a l e s and h i g h l y a c t i v e a t h l e t e s t h e most ( B e n t l e y and Dowd, 1 9 8 4 ) . However , o t h e r r e p o r t s i n t h e l i t e r a t u r e s u g g e s t t h a t i t r e l a t e s t o s p o r t s a c t i v i t y o r t r auma (G rana e t a l . 1 9 8 4 ) , and i s e q u a l l y common among bo t h s exe s ( R e y n o l d s e t a l . 1 9 8 3 ) . The p a i n i s o f t e n a d u l l , a c h i n g one t h a t may be b e h i n d t h e p a t e l l a , o r a l o n g t h e m e d i a l b o r d e r , o r w h i c h may e v e n t u a l l y r a d i a t e i n a l l d i r e c t i o n s (Ma lek and Mang i n e , 1 9 8 1 ) . The p a i n may be a g g r a v a t e d by s i t t i n g w i t h t h e knees b e n t f o r l o n g p e r i o d s (mov i e s i g n ) o r by a c t i v i t y wh i c h l o a d s t h e p a t e l l o f e m o r a l j o i n t d u r i n g f l e x i o n ( i e . - s q u a t t i n g , a s c e n d i n g o r d e s c e n d i n g s t a i r s ) . S w e l l i n g i s n o t common b u t may be m i l d y p r e s e n t , t h e r e i s no h i s t o r y o f ' l o c k i n g ' as seen w i t h m e n i s c a l t e a r s , b u t t h e p a t i e n t may c o m p l a i n o f a s e n s a t i o n o f ' g i v i n g way ' o f t h e k n e e . C r e p i t i s may be p r e s e n t d u r i n g movement o f t h e p a t e l l a and t h e p a t i e n t w i l l o f t e n n o t e a s t i f f n e s s o r t i g h t n e s s a t t h e k n e e , e s p e c i a l l y a f t e r a c t i v i t y . One may a l s o n o t e t h a t c o m p r e s s i o n o f t h e p a t e l l a a g a i n s t t h e f emo r a l c o n d y l e s w i l l e l i c i t p a i n . M u s c l e t e s t i n g may r e v e a l weakness o f t h e q u a d r i c e p s a n d / o r t h e h a m s t r i n g s g r o u p s . The s t r e n g t h o f t h e h a m s t r i n g s has been f o u n d t o be l e s s t h a n t h a t o f t h e q u a d r i c e p s i n a normal knee ( N o s s e , 1 9 8 2 ) . The r e l a t i o n s h i p between t h e s t r e n g t h o f t h e f l e x o r s t o t h e e x t e n s o r s has been r e p o r t e d by Nosse (1982) t o v a r y between 43-90%, depend i ng upon t h e - 88 - a n g u l a r v e l o c i t y . I t has been s u g g e s t e d t h a t t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s s h o u l d have equa l s t r e n g t h so t h a t t h e y c o n t r i b u t e t o t h e c o r r e c t a l i g n m e n t o f t h e p a t e l l a ( R e y n o l d s e t a l . 1 9 8 3 ) . In t e rms o f q u a d r i c e p s weakne s s , t h e l i t e r a t u r e p r e s e n t s d i f f e r e n t v i e w s . M a r i a n i and C a r u s o (1979) have r e p o r t e d t h a t q u a d r i c e p s weakness i s a t t r i b u t a b l e s p e c i f i c a l l y t o v a s t u s m e d i a l i s w e a k n e s s . However , W i l d e t a l . ( 1 9 8 2 ) , b e l i e v e t h a t weakness o f t h e q u a d r i c e p s i s n o t s p e c i f i c t o t h e v a s t u s m e d i a l i s b u t r a t h e r i n d i c a t i v e o f weakness o f a l l o f t h e q u a d r i c e p s . Measurement o f t h e Q - a n g l e , w h i c h i s t h e a n g l e between t h e l i n e o f p u l l o f t h e q u a d r i c e p s and t h e p a t e l l a r t e n d o n , i s o f t e n above 15° i n p a t i e n t s w i t h PFPS (S chambe rge r , 1 9 8 3 ) . A Q -ang l e above 15° may be i n d i c a t i v e o f l a t e r a l t r a c k i n g o f t h e p a t e l l a (LeVeau & B e r n h a r d t , 1984) b u t by i t s e l f t h e Q - ang l e i s n o t d i a g n o s t i c o f P F PS . I t i s o f t e n a s s o c i a t e d w i t h o t h e r d e f i c i e n c i e s o f t h e e x t e n s o r mechan i sm. Lower e x t r e m i t y a l i g n m e n t must be a s s e s s e d as t o r s i o n a l o r a n g u l a r m a l a l i g n m e n t s have a s i g n i f i c a n t i n f l u e n c e on t h e mechan i c s o f t h e p a t e l l o f e m o r a l j o i n t . James (1979) d e s c r i b e s one g roup o f t o r s i o n a l d e f o r m i t i e s t h a t he has r e f e r r e d t o a s ' m i s e r a b l e m a l a l i g n m e n t ' . I n c r e a s e d i n t e r n a l h i p r o t a t i o n ( f e m o r a l neck a n t e v e r s i o n ) may be compensa ted f o r by e x t e r n a l r o t a t i o n o f t h e t i b i a so t h a t t h e f e e t a r e p l a c e d f o r w a r d r a t h e r t h a n i n - t o e i n g . T h i s r e s u l t s i n an i n c r e a s e d Q - a n g l e , as t h e t i b i a l t u b e r c l e i s e x t e r n a l l y r o t a t e d . These p a t i e n t s w i l l o f t e n have genu varum and r e c u r v a t u m , s q u i n t i n g p a t e l l a e , a h i g h r i d i n g p a t e l l a ( p a t e l l a a l t a ) and compensa t o r y p r o n a t i o n o f t h e f o o t . - 89 - Normal a l i g n m e n t o f t h e knee i s c o n s i d e r e d t o be i n s l i g h t v a l g u s a n g u l a t i o n (170°) as t h e femur i s d i r e c t e d m e d i a l l y f r om t h e p e l v i s t o a r t i c u l a t e w i t h t h e t i b i a . A n g l e s much s m a l l e r o r g r e a t e r t h a n 170° a r e c o n s i d e r e d t o be abnormal and r e f e r r e d t o a s genu va l gum o r genu va rum, r e s p e c t i v e l y (Lehmkuhl and S m i t h , 1 9 8 3 ) . The p r e s e n c e o f genu va lgum may be a s s o c i a t e d w i t h i n c r e a s e d e x t e r n a l r o t a t i o n o f t h e t i b i a o r w i t h compensa to r y p r o n a t i o n o f t h e f o o t . In t h i s s i t u a t i o n , t h e Q - ang l e i s i n c r e a s e d by t h e e x t e r n a l r o t a t i o n o f t h e t i b i a (LeVeau & B e r n h a r d t , 1 9 8 4 ) . A n o t h e r r e l a t i o n s h i p t h a t must be e v a l u a t e d i s t h a t o f t h e f u n c t i o n o f t h e f o o t d u r i n g w a l k i n g and r u n n i n g , and i t s a f f e c t upon t h e knee and t h e p a t e l l o f e m o r a l j o i n t i n p a r t i c u l a r . As t h e speed o f g a i t i n c r e a s e s t h e magn i t ude o f t h e f o r c e s t h r o u g h t h e l o w e r e x t r e m i t y i n c r e a s e s (Mann, 1982) and any b i o m e c h a n i c a l d i s c r e p a n c i e s t h a t e x i s t w i l l a l s o be a m p l i f i e d (S chambe rge r , 1 9 8 3 ) . N o r m a l l y as t h e f o o t s t r i k e s t h e g round t h e r e i s a r a p i d p e r i o d o f p r o n a t i o n w h i c h r e a c h e s i t s maximum a t a p p r o x i m a t e l y 35-45% o f t h e s t a n c e phase i n r u n n i n g (Smar t e t a l . 1 9 8 0 ) . As t h e f o o t i s p r o n a t i n g , t h e t i b i a i s i n t e r n a l l y r o t a t e d and t h e knee i s f l e x i n g . The p r o n a t e d f o o t i s a f l e x i b l e one w h i c h i s a b l e t o a b s o r b shock and a d a p t t o t h e g round s u r f a c e (Lehmukuhl and S m i t h , 1 9 8 3 ) . A t t h e same t i m e , t h e knee f l e x i o n i s a l s o a shock a b s o r b i n g mechan ism ( W i n t e r , 1 9 8 3 ) . A t a p p r o x i m a t e l y 70% o f t h e s t a n c e p h a s e , t h e f o o t s u p i n a t e s , t h e t i b i a e x t e r n a l l y r o t a t e s and t h e knee e x t e n d s . I f p r o n a t i o n o f t h e f o o t and i n t e r n a l r o t a t i o n o f t h e t i b i a a r e p r o l o n g e d i n t o l a t e r s t a n c e when t h e knee i s e x t e n d i n g o r i f t h ey a r e e x c e s s i v e , t h en t h e r e w i l l be i n c r e a s e d s t r e s s t h r o u g h t h e f o o t and an - 90 - i n c r e a s e i n t r a n s v e r s e r o t a t i o n w h i c h must be a b s o r b e d a t t h e k n e e . A d i s t u r b a n c e i n t h e t i b i o f e m o r a l r o t a t i o n a l r e l a t i o n s h i p w i l l c a u s e abnormal j o i n t s t r e s s e s and w i l l a l t e r t h e p a t e l l o f e m o r a l mechan i c s ( B a t e s e t a l . 1 9 7 9 ) . A n e u t r a l f o o t i s one t h a t w i l l f u n c t i o n t h e most e f f i c i e n t l y w i t h l e a s t s t r a i n on t h e j o i n t s , l i g a m e n t s , and t e n d o n s , and w h i c h r e q u i r e s m in ima l e x e r t i o n by t h e m u s c l e s o f t h e f o o t i n s t a n c e ( J ames , 1 9 7 9 ) . James a l s o has o b s e r v e d f r om h i s c l i n i c a l d a t a t h a t i n a n o n w e i g h t - b e a r i n g p o s i t i o n ( p r one l y i n g ) t h e v e r t i c a l a x i s o f t h e hee l s h o u l d be p a r a l l e l t o t h e d i s t a l one t h i r d o f t h e t i b i a , w i t h t h e s u b t a l a r j o i n t n e u t r a l ( r e a r f o o t a l i g n m e n t ) . F o r e f o o t - hee l a l i g n m e n t i s c o n s i d e r e d normal when t h e p l a n e o f t h e m e t a t a r s a l heads i s p e r p e n d i c u l a r t o t h e v e r t i c a l a x i s o f t h e h e e l . A c c o r d i n g t o Taun ton e t a l . (1985) normal r e a r f o o t v a r u s i s c o n s i d e r e d t o be 3° and f o r e f o o t v a r u s 2 ° . E x c e s s i v e o r c ompensa t o r y p r o n a t i o n o f t h e f o o t i n w e i g h t - b e a r i n g o c c u r s when t h e r e i s m a l a l i g n m e n t o f t h e l e g / h e e l r e l a t i o n s h i p ( i n c r e a s e d r e a r f o o t v a r u s ) o r m a l a l i g n m e n t o f t h e h e e l / f o r e f o o t r e l a t i o n s h i p . In b o t h c a s e s t h e f o o t w i l l o v e r p r o n a t e t o a c h i e v e c o n t a c t w i t h t h e g round (James e t a l . 1 9 7 8 ) . Etiology of Patellofemoral Pain A v a r i e t y o f f a c t o r s have been s u g g e s t e d as p o s s i b l e c a u s e s o f p a t e l l o - f emo r a l p a i n ; among t h e s e a r e d e g e n e r a t i v e d i s e a s e s , r e p e a t e d m i n o r t r a u m a , a c u t e s e v e r e t r auma and m a l a l i g n m e n t o f t h e p a t e l l o f e m o r a l e x t e n s o r mechan ism (Ma lek and M a n g i n e , 1 9 8 1 ) . R e i d e r e t a l . (1981) s u g g e s t t h a t abnormal p a t e l l a r t r a c k i n g , s e c onda r y t o m a l a l i g n m e n t o f t h e - 91 - q u a d r i c e p s - p a t e l l a r mechan i sm, i s a m a j o r e t i o l o g i c a l f a c t o r . James (1979) r e p o r t s t h a t i n h i s e x p e r i e n c e , e x t e n s o r mechan ism m a l a l i g n m e n t i s t h e most f r e q u e n t l y i m p l i c a t e d e t i o l o g i c a l f a c t o r . He a l s o empha s i z e s t h e r o l e o f t h e l o w e r e x t r e m i t y a l i g n m e n t i n t h e e t i o l o g y o f p a t e l l o f e m o r a l j o i n t p r o b l e m s . James (1979) b e l i e v e s t h a t t h e a r t i c u l a r c a r t i l a g e o f t h e p a t e l l a i s a s e n s i t i v e i n d i c a t o r o f abnormal knee j o i n t me chan i c s b u t he a l s o adds t h a t t h e deve l opmen t o f p a i n i s n o t d i r e c t l y f r om t h e a r t i c u l a r c a r t i l a g e , as i t i s d e v o i d o f p a i n f i b r e s and b l o o d v e s s e l s . F i c a t and H u n g e r f o r d (1977) s u g g e s t t h a t i n a normal d i a r t h r o d i a l j o i n t t h e r e a r e two s o u r c e s f o r t h e p a i n f u l s t i m u l i : t h e r i c h l y i n n e r v a t e d s ynov i um and t h e s u b c h o n d r a l bone . The i n t e g r i t y o f t h e a r t i c u l a r c a r t i l a g e i s e s s e n t i a l t o j o i n t l u b r i c a t i o n and b i o m e c h a n i c a l f u n c t i o n , and t o t h e n u t r i t i o n o f t h e c a r t i l a g e i t s e l f . A r t i c u l a r c a r t i l a g e n u t r i t i o n i s dependen t upon d i f f u s i o n o f t h e n u t r i e n t s f r om s u p e r f i c i a l t o deep l a y e r s o f t h e c a r t i l a g e e s p e c i a l l y d u r i n g p e r i o d s o f n o n - c o m p r e s s i o n . Under c o m p r e s s i o n t h e deepe r f i b r e s a r e l e s s pe rmeab l e and r e s i s t t h e i n t e r s t i t i a l f l o w o f f l u i d . V a r y i n g d e g r e e s o f c o m p r e s s i o n a l s o a f f e c t s t h e p r o t e o g l y c a n component o f t h e g round s u b s t a n c e , so t h a t f l u i d e s c a p e s f r om t h e a r t i c u l a r c a r t i l a g e when compres sed b u t i s r e a b s o r b e d d u r i n g p e r i o d s o f n o n - c o m p r e s s i o n . T h i s i s t h e b a s i s f o r j o i n t l u b r i c a t i o n . As an a d v a n c i n g c o m p r e s s i v e l o a d moves t owa rd s non - compre s sed a r e a s , f l u i d i s pushed a l o n g t h e l e a d i n g e d g e . D e c r e a s e d p e r m e a b i l i t y o f t h e a r t i c u l a r - 92 - c a r t i l a g e o c c u r s unde r t h e l o a d and a l u b r i c a t i n g f i l m i s m a i n t a i n e d on t h e s u r f a c e , w h i l e t h e c a r t i l a g e r e t u r n s t o normal p e r m a b i l i t y i n non - compres sed a r e a s ( J ames , 1 9 7 9 ) . F i c a t and H u n g e r f o r d (1977) have shown unde r l o c a l a n e s t h e t i c , t h a t d i r e c t p r e s s u r e on s o f t e n e d b u t i n t a c t a r t i c u l a r c a r t i l a g e r e p r o d u c e d t h e p a t i e n t ' s p a t e l l o f e m o r a l p a i n , whereas p r e s s u r e on f i r m , h e a l t h y c a r t i l a g e was n o t d e t e c t e d by t h e p a t i e n t . T h i s has l e d them and o t h e r s ( J ames , 1979) t o t h e h y p o t h e s i s t h a t e a r l y changes i n t h e a r t i c u l a r c a r t i l a g e o c c u r a t deep l a y e r s and a f f e c t t h e e n e r g y - a b s o r b i n g c a p a c i t y o f t h e c a r t i l a g e , w h i c h r e s u l t s i n abnorma l t r a n s m i s s i o n o f f o r c e s t o t h e s u b c h o n d r a l bone , and u l t i m a t e l y t o t h e deve l opmen t o f p a i n . Normal p a t e l l a r c o n t a c t w i t h t h e femur p a s s e s f r om d i s t a l t o p r o x i m a l as t h e knee f l e x e s . Up t o 135° o f f l e x i o n a l l o f t h e c a r t i l a g e a r t i c u l a t e s w i t h t h e f emur a t some p o i n t i n t h e r a n g e , e x c e p t f o r t h e odd f a c e t ( F i c a t and H u n g e r f o r d , 1 9 7 7 ) . By 135° t he m e d i a l f a c e t l i e s f r e e i n t h e i n t e r c o n d y l a r g r oove and t h e odd f a c e t c o n t a c t s t h e m e d i a l f emo r a l c o n d y l e . K e s s l e r and H e r t l i n g (1983) p o i n t o u t t h a t t h i s v e r y l a t e c o n t a c t makes t h e odd f a c e t an a r e a o f n o n - a r t i c u l a t i o n i n most e v e r y d a y a c t i v i t i e s , w h i c h may r e n d e r t h e a r t i c u l a r c a r t i l a g e n u t r i t i o n a l l y d e f i c i e n t . T h i s phenomenon w o u l d become i m p o r t a n t i n t h e c a s e o f abnorma l l a t e r a l t r a c k i n g o f t h e p a t e l l a , w h i c h b r i n g s t h e odd f a c e t i n t o e a r l i e r c o n t a c t w i t h t h e m e d i a l c o n d y l e . P oo r n u t r i t i o n may c au s e t h e c a r t i l a g e t o be weakened and s o f t e n e d and as such i t wou l d be u n a b l e t o t o l e r a t e t h e unaccus tomed f o r c e s . - 93 - O t h e r c a u s e s o f a r t i c u l a r c a r t i l a g e breakdown may i n v o l v e c a r t i l a g e t h a t i s o t h e r w i s e h e a l t h y and w e l l - n o u r i s h e d , b u t i s o v e r l o a d e d by e x c e s s i v e p a t e l l o f e m o r a l j o i n t r e a c t i o n f o r c e s . F o r e x amp l e , t h i s may o c c u r i n a p a t e l l a w i t h a s m a l l e r t h a n normal m e d i a l f a c e t , i n w h i c h a s m a l l a r e a i s s u b j e c t e d t o i n c r e a s e d f o r c e s . The l a t e r a l f a c e t may a l s o be a f f e c t e d by a b n o r m a l l y h i g h j o i n t r e a c t i o n f o r c e s . One p o s s i b l e c au s e o f i n c r e a s e d l a t e r a l p r e s s u r e i s e x c e s s i v e t i g h t e n i n g , t h i c k e n i n g , o r s c l e r o s i s o f t h e l a t e r a l r e t i n a c u l u m ( F i c a t and H u n g e r f o r d , 1 9 7 7 ) . These a u t h o r s have r e p o r t e d t h a t many d y s p l a s i a s o f t h e p a t e l l a have been n o t e d t o g e t h e r w i t h what t h e y c a l l e x c e s s i v e l a t e r a l p r e s s u r e synd rome . They b e l i e v e t h a t g r e a t e r t h a n normal l a t e r a l p r e s s u r e on t h e p a t e l l a d u r i n g g rowth may a l t e r t h e shape o f t h e p a t e l l a , and u l t i m a t e l y , may l e a d t o changes i n t h e r e t r o a r t i c u l a r c a r t i l a g e . LeVeau & B e r n h a r d t (1984) s u g g e s t , t h a t when t h e l a t e r a l c o n n e c t i v e t i s s u e s a r e t i g h t t h e m e d i a l s o f t t i s s u e s a r e s t r e s s e d and s t r e t c h e d , w h i c h may r e s u l t i n p a i n and i n f l a m m a t i o n i n t h o s e t i s s u e s . A n o t h e r s o u r c e o f p a i n , t h a t i s r e l a t e d t o t h e w e l l i n n e r v a t e d s y n o v i u m , may be imp ingement o f p l i c a ( J ames , 1 9 7 9 ) . P l i c a i s an e x t e n s i o n o f s y n o v i a l t i s s u e w h i c h can become compres sed between one o f t h e f emo r a l c o n d y l e s and t h e p a t e l l a . I t o r i g i n a t e s e i t h e r m e d i a l l y o r l a t e r a l l y , mos t o f t e n l a t e r a l l y , and e x t e n d s t o t h e o t h e r s i d e o f t h e p a t e l l o f e m o r a l j o i n t , i n c l u d i n g t h e i n f e r i o r f a t p a d . When i t i s c h r o n i c a l l y i m p i n g e d i t becomes t h i c k e n e d and t h e p a t i e n t c o m p l a i n s o f p a i n and t e n d e r n e s s a c r o s s t h e m e d i a l o r l a t e r a l f emo r a l c o n d y l e and a ' s n a p p i n g ' o r ' c a t c h i n g ' s e n s a t i o n . - 94 - The p r e s e n t - d a y know ledge c o n c e r n i n g t h e mechan ism o f p a i n i n PFPS s u g g e s t s t h a t an a l t e r a t i o n i n t h e mechan i c s o f t h e p a t e l l o f e m o r a l j o i n t may r e s u l t i n i n c r e a s e d p a t e l l o f e m o r a l j o i n t r e a c t i o n f o r c e s w h i c h t h e a r t i c u l a r c a r t i l a g e and s u b c h o n d r a l bone a r e u n a b l e t o t o l e r a t e . B a s m a j i a n (1970) b e l i e v e s t h a t due t o j o i n t p a i n one v o l u n t a r i l y i n h i b i t s movement, w h i c h r e s u l t s i n weakness and p o s s i b l e a t r o p h y o f t h e s u r r o u n d i n g m u s c l e s . However , i n an a t t e m p t t o e x p l a i n t h e deve l opmen t o f p a i n i n a j o i n t , F i c a t and H u n g e r f o r d (1977) c a u t i o n t h a t t h e r e i s s t i l l c o n s i d e r a b l e room f o r g r e a t e r u n d e r s t a n d i n g o f t h e p a t h o p h y s i o l o g y o f p a i n f u l j o i n t s . The r e i s a l s o a need t o r e c o g n i z e t h a t t h e e t i o l o g i c a l f a c t o r s o f PFPS a r e numerous and m u l t i f a c t o r i a l , and as such a l s o may n o t be c o m p l e t e l y u n d e r s t o o d . - 95 - ELECTROMYOGRAPHY E l e c t r o m y o g r a p h y (EMG) i s t h e g r a p h i c a l r e c o r d i n g o f t h e e l e c t r i c a l a c t i v i t y o f m u s c l e s . I t r e p r e s e n t s t h e summat ion o f a l l t h e m u s c l e a c t i o n p o t e n t i a l s a f t e r b e i n g t r a n s m i t t e d t h r o u g h t h e m u s c l e t i s s u e s . V o l u n t a r y i s o m e t r i c c o n t r a c t i o n s r e s u l t i n a n o n - l i n e a r i n c r e a s e i n t h e i n t e g r a t e d EMG a c t i v i t y ( V r e d e n b r e g t & Rau , 1 9 7 3 ) , howeve r , t h e r e a r e many f a c t o r s w h i c h a f f e c t t h e r e c o r d i n g o f t h e EMG s i g n a l , such as e l e c t r o d e p l a c e m e n t , amount o f s ub cu t aneou s f a t , s k i n t e m p e r a t u r e , a n d / o r mus c l e mass t h a t a l l o w c o n s i d e r a b l e v a r i a b i l i t y among s u b j e c t s o r between t r i a l s ( W i n t e r , 1 9 8 4 ) . A b i o l o l o g i c a l a m p l i f i e r f o r t h e r e c o r d i n g o f t h e EMG can use e i t h e r s u r f a c e e l e c t r o d e s o r i n d w e l l i n g e l e c t r o d e s . The a m p l i f i e r s h o u l d c on f o rm t o c e r t a i n s p e c i f i c a t i o n s i n r e g a r d t o t h e g a i n , i n p u t impedence , f r e q u e n c y r e s p o n s e , and CMRR, so t h a t i t g e n e r a t e s a ' c l e a n ' s i g n a l ; one t h a t i s u n d i s t o r t e d and f r e e o f a r t i f a c t s o r ' n o i s e ' ( I S E K , 1 9 8 0 ) . S u r f a c e EMG has a f r e q u e n c y r ange o f 5 - 2000 Hz. The e l e c t r o d e s a r e p l a c e d c l o s e l y t o g e t h e r (no more t h a n 5 cm. a p a r t ) as recommended by Komi and B u s k i r k (1970) o v e r t h e mo to r p o i n t o f t h e m u s c l e o r t h e m u s c l e b e l l y . Each e l e c t r o d e / s k i n i n t e r f a c e has a f i n i t e impedence d epend i ng upon t h e t h i c k n e s s o f t h e s k i n , c l e a n l i n e s s o f t h e s k i n , a r e a o f t h e e l e c t r o d e s u r f a c e and t e m p e r a t u r e o f t h e e l e c t r o d e p a s t e . P e r r y (1981) and P e r r y e t a l . (1981) have s u g g e s t e d t h a t s u r f a c e e l e c t r o d e s r e p r e s e n t g roup m u s c l e a c t i v i t y o r t h e common a c t i v i t y o f a g roup o f s u p e r f i c i a l m u s c l e s . A l t h o u g h t h e y r e p o r t e d i n 1981 t h a t s u r f a c e - 96 - e l e c t r o d e s r e f l e c t l e s s t h a n one t e n t h o f t h e a c t i v i t y s en sed by i n d w e l l i n g e l e c t r o d e s , B o u i s s e t and Maton (1972) have r e p o r t e d a l i n e a r r e l a t i o n s h i p between t h e o u t p u t o f s u r f a c e e l e c t r o d e s and i n d w e l l i n g e l e c t r o d e s . However , more r e c e n t l y , Schwab e t a l . (1983) have r e c o g n i z e d t h a t s u r f a c e e l e c t r o d e s a r e t h e p r a c t i c a l c h o i c e o v e r i n d w e l l i n g e l e c t r o d e s i n t h a t s u b j e c t c o m p l i a n c e t o a s t u d y i s i m p r o v e d . In f a c t , i n t h e i r s t u d y c o m p a r i n g o v e r g r o u n d t o t r e a d m i l l r u n n i n g and t h e use o f s u r f a c e e l e c t r o d e s and i n d w e l l i n g e l e c t r o d e s , t h e y f ound no s i g n i f i c a n t d i f f e r e n c e i n t h e t empo ra l p a t t e r n s o f m u s c l e a c t i v i t y . Once t h e EMG s i g n a l has been c o l l e c t e d and a m p l i f i e d , i t i s u s u a l l y p r o c e s s e d so t h a t i t may be more e a s i l y compared w i t h o t h e r b i o m e c h a n i c a l s i g n a l s . L i n e a r e n v e l o p e EMG i s one method o f p r o c e s s i n g t h a t f o l l o w s t h e t r e n d o f t h e EMG and c l o s e l y r e s e m b l e s t h e shape o f t h e t e n s i o n c u r v e . In o t h e r w o r d s , i t b e a r s some r e l a t i o n s h i p t o t h e b i o m e c h a n i c s o f movement ( W i n t e r , 1 9 7 9 ) . W i n t e r (1984) a l s o b e l i e v e s t h a t l i n e a r e n v e l o p e p r o c e s s i n g i s t h e b e s t method f o r p r o d u c i n g an a n a l o g p a t t e r n t h a t i s r e l i a b l e and r e p r o d u c i b l e . To f u r t h e r imp rove t h e r e l i a b i l i t y o f t h e EMG i n g a i t a n a l y s i s , t h e g a i t c y c l e t i m e base i s n o r m a l i z e d t o 100% and t h e l i n e a r e n v e l o p e i s a v e r a g e d f r om a number o f s t r i d e s t o o b t a i n an ensemb le a v e r age f o r each mus c l e f o r a c e r t a i n g roup o f s u b j e c t s ( W i n t e r , 1984; R i c h a r d s e t a l . 1 9 8 5 ) . Some a u t h o r s have u sed a maximum v o l u n t a r y i s o m e t r i c c o n t r a c t i o n as a be tween-day and b e t w e e n - s u b j e c t n o r m a l i z a t i o n method i n EMG g a i t s t u d i e s (Dubo e t a l . 1 9 7 6 ) . However , Yang and W i n t e r (1983) have r e p o r t e d t h a t - 97 - t h i s i s n o t t h e most r e l i a b l e method o f c ompa r i n g a m p l i t u d e m e a s u r e s . In 1984 Yang and W i n t e r i n v e s t i g a t e d f o u r t y p e s o f n o r m a l i z a t i o n , two o f w h i c h where d e r i v e d f r om i s o m e t r i c c a l i b r a t i o n and two o f w h i c h were c a l c u l a t e d f r om w a l k i n g t r i a l s , t o d e t e r m i n e i f t h e b e t w e e n - s u b j e c t v a r i a b i l i t y c o u l d be d e c r e a s e d . The l a t t e r two methods i n v o l v e d n o r m a l i z i n g t o t h e peak o f t h e w i t h i n - s u b j e c t ensemb le a v e r age o r t o t h e mean o f t h e w i t h i n - s u b j e c t ensemb le a v e r a g e . In b o t h c a s e s t h e r e was a l a r g e r e d u c t i o n o f b e t w e e n - s u b j e c t v a r i a b i l i t y , howeve r , i t was a t t h e expense o f i n f o r m a t i o n t h a t may have been o b t a i n e d f r om t h e EMG a m p l i t u d e m e a s u r e s . T h e r e f o r e when t h e EMG a m p l i t u d e i s an i n t e g r a l p a r t o f a s t u d y n o r m a l i z i n g t o t h e ensemb le a v e r age wou l d r e du ce i t s s i g n i f i c a n c e . - 98 - BIOMECHANICAL STUDIES OF RUNNING EMG s t u d i e s , e l e c t r o g o r i i o m e t e r and m e c h a n i c a l power a n a l y s e s have c o n t r i b u t e d immense ly t o t h e know ledge o f m u s c l e and j o i n t a c t i v i t y d u r i n g r u n n i n g . F o r e x amp l e , c e r t a i n e l e c t r o g o n i o m e t r i c i n v e s t i g a t i o n s ( Taun ton e t a l . 1985) have d e s c r i b e d t h r e e d i m e n s i o n a l a n g u l a r m o t i o n a t t h e knee and t h e f o o t d u r i n g t r e a d m i l l r u n n i n g . These i n v e s t i g a t o r s have e l a b o r a t e d on t h e t i m i n g and deg r ee s o f p l a n t a r f l e x i o n , d o r s i f l e x i o n , e v e r s i o n , i n v e r s i o n , a b d u c t i o n and a d d u c t i o n a t t h e f o o t and knee f l e x i o n and e x t e n s i o n , v a l g u s and v a r u s , and i n t e r n a l and e x t e r n a l r o t a t i o n d u r i n g one g a i t c y c l e . An EMG s t u d y o f t h e m u s c l e a c t i v i t y d u r i n g t r e a d m i l l r u n n i n g by E l l i o t t & B l a n k s b y (1979) r e v e a l e d t h a t t h e v a s t u s l a t e r a l i s , t h e v a s t u s m e d i a l i s and r e c t u s f e m o r i s were a l l a c t i v e a t h e e l - s t r i k e w i t h t h e i r peak a m p l i t u d e s o c c u r r i n g between h e e l - s t r i k e and h e e l - o f f . A t a speed o f 3 .5 m/s ( a p p r o x i m a t e l y 12 k m / h ) , t h e a v e r a g e i n t e g r a t e d EMG o f t h e v a s t u s m e d i a l i s had t h e h i g h e s t a m p l i t u d e and r e c t u s f e m o r i s had t h e l e a s t a m p l i t u d e o f t h e t h r e e m u s c l e s . The v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s had d e c r e a s i n g mus c l e a c t i v i t y , f r om t h e peak i n m i d s t a n c e t o e a r l y s w i n g . R e c t u s f e m o r i s a c t i v i t y had d e c r e a s e d by t h e o n s e t o f sw i ng p h a s e , b u t had a n o t h e r b u r s t o f a c t i v i t y d u r i n g s w i n g . In a n o t h e r EMG s t u d y o f r u n n i n g , Mann (1982) r e p o r t e d q u a d r i c e p s a c t i v i t y f o r 50-60% o f t h e s t a n c e phase i n r u n n i n g . He a l s o n o t e d q u a d r i c e p s a c t i v i t y a t t h e end o f sw i ng p h a s e , b u t u n f o r t u n a t e l y he d i d n o t d i s t i n g u i s h among t h e v a r i o u s m u s c l e s w i t h i n t h e q u a d r i c e p s . M e c h a n i c a l power a n a l y s e s o f r u n n i n g ( W i n t e r , 1983; R o b e r t s o n & T a u n t o n , 1982; R o b e r t s o n , i n p r e s s ) have shown s t r o n g e c c e n t r i c e x t e n s o r - 99 - m u s c l e a c t i v i t y a t t h e knee i m m e d i a t e l y a f t e r h ee l c o n t a c t and up t o m i d s t a n c e . From m i d s t a n c e t o p u s h - o f f t h e e x t e n s o r s worked c o n c e n t r i c a l l y . A t p u s h - o f f t h e e x t e n s o r s were s t i l l d om inan t b u t w o r k i n g e c c e n t r i c a l l y . From t h e r e s u l t s o f t h e power a n a l y s e s , i t has been s u g g e s t e d t h a t t h e q u a d r i c e p s work e c c e n t r i c a l l y i n e a r l y s t a n c e t o c o n t r o l knee f l e x i o n as t h e f o o t h i t s t h e g round - a shock a b s o r b i n g mechan ism ( W i n t e r , 1 9 8 3 ) . R o b e r t s o n & Taun ton (1982) r e p o r t e d t h i s e x t e n s o r moment t o r ange between 150-350 N.m and t h e ene r gy a b s o r p t i o n t o r ange between 25-105 j o u l e s . From m i d s t a n c e t o l a t e s t a n c e t h e q u a d r i c e p s were c o n t r a c t i n g c o n c e n t r i c a l l y as t h e knee e x t e n d s i n p r e p a r a t i o n f o r p u s h - o f f . T h i s c o n c e n t r i c c o n t r a c t i o n d i s s i p a t e d 11-44 j o u l e s o f e n e r g y . A t t h e v e r y end o f s t a n c e phase a s m a l l e r e c c e n t r i c c o n t r a c t i o n o f t h e q u a d r i c e p s d e c e l e r a t e d t h e f l e x i n g knee a c c o r d i n g t o W i n t e r ( 1 9 8 3 ) . T h i s n e g a t i v e work by t h e e x t e n s o r s a b s o r b e d a p p r o x i m a t e l y 11 j o u l e s o f e n e r g y . D u r i n g sw i ng phase t h e r e s u l t s o f t h e power a n a l y s i s ( W i n t e r , 1983) showed a l a c k o f c o n t r i b u t i o n by t h e knee e x t e n s o r s t o t h e f o r w a r d s w i n g i n g l e g and f o o t . The EMG d a t a f r om E l l i o t t & B l a n k s b y (1979) p r o v i d e d e v i d e n c e t h a t t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s were t h e mos t a c t i v e q u a d r i c e p s d u r i n g e a r l y s t a n c e and t h e r e f o r e may be r e s p o n s i b l e f o r most o f t h e shock a b s o r p t i o n a t t h e k n e e . R e c t u s f e m o r i s a l s o c o n t r i b u t e d t o t h i s f u n c t i o n b u t t o a l e s s e r e x t e n t . T h e i r s t u d y showed t h a t t h e v a s t u s m e d i a l i s and t h e v a s t u s l a t e r a l i s c o n t i n u e d t o be more a c t i v e t h r o u g h o u t t h e b a l a n c e o f t h e s t a n c e p h a s e . E l l i o t t & B l a n k s b y (1979) have r e p o r t e d t h e EMG a c t i v i t y i n r e c t u s f e m o r i s d u r i n g sw i ng as a c t i n g as a h i p f l e x o r . Power a n a l y s e s o f t h e h i p - 100 - d u r i n g r u n n i n g have n o t r e v e a l e d a p a t t e r n t h a t i s c o n s i s t e n t enough t o be r e p o r t e d and t h e r e f o r e can n o t c o n f i r m t h e EMG r e s u l t s . - 101 - ISOKINETIC DYNAMOMETRY The a b i l i t y t o measure mus c l e s t r e n g t h as i t r e l a t e s t o f u n c t i o n a l a c t i v i t y i s e s s e n t i a l t o o u r u n d e r s t a n d i n g o f normal p e r f o r m a n c e . M u s c l e s t r e n g t h c an be d e f i n e d as t h e a b i l i t y o f a s i n g l e m u s c l e o r a mus c l e g roup t o e x e r t max ima l f o r c e i n a s i n g l e v o l u n t a r y e f f o r t ( K n a p i k and Ramos, 1980) o r a s Mu r r a y e t a l . (1980) d e f i n e i t - i t i s t h e r o t a t i o n a l component , o r t o r q u e , p r odu ced by a m u s c l e . T h i s s t r e n g t h can be measured i s o m e t r i c a l l y , w h i c h measures t h e m u s c l e f o r c e o n l y a t a s p e c i f i c j o i n t a n g l e , o r i t can be measured unde r t h e dynamic c o n d i t i o n s o f i s o t o n i c o r i s o k i n e t i c a c t i v i t y . I s o k i n e t i c m u s c l e a c t i v i t y i s a r e l a t i v e l y new c o n c e p t , w h i c h H i s l o p and P e r r i n e , and T h i s t l e and c o w o r k e r s i n t r o d u c e d i n 1967 . P e r r i n e (1968) d e f i n e d i s o k i n e t i c e x e r c i s e as e x e r c i s e w h i c h o c c u r s a g a i n s t a l o a d w h i c h a l l o w s movement a t a m e c h a n i c a l l y f i x e d r a t e o f speed and o f f e r s r e s i s t a n c e i n h e r e n t l y p r o p o r t i o n a l t o t h e m u s c l e ' s dynamic t e n s i o n d e v e l o p i n g c a p a c i t y a t e v e r y p o i n t i n i t s r a n g e . The accommodat ing r e s i s t a n c e s u p p l i e d by an e l e c t r o m e c h a n i c a l d e v i c e , c a l l e d an i s o k i n e t i c dynamometer , a l l o w s f o r t h e c o n t i n u o u s l y c h a n g i n g m u s c l e t e n s i o n t h a t o c c u r s w i t h c h a n g i n g l e v e r a g e t h r o u g h o u t t h e movement. S i n c e t h e l a t e 1 9 6 0 ' s when an i s o k i n e t i c dynamometer (Cybex) was i n t r o d u c e d t o No r t h A m e r i c a i t has been p o s s i b l e t o s t u d y t h e m e c h a n i c a l p r o p e r t i e s o f m u s c l e unde r c o n d i t i o n s o f c o n s t a n t s p e e d , i n v i v o . Such p r o p e r t i e s as t h e maximal f o r c e c u r v e , t h e w o r k , power , and endu rance c a p a c i t i e s o f m u s c l e have been measu red c o n c e n t r i c a l l y . - 102 - U s i n g t h e i s o k i n e t i c dynamometer , r e s e a r c h e r s have s t u d i e d t h e r e l a t i o n s h i p between a n g u l a r v e l o c i t y and t o r q u e v a l u e s d u r i n g c o n c e n t r i c c o n t r a c t i o n s ( T h o r t e n s s o n e t a l . 1 9 7 6 ) . These i n v e s t i g a t i o n s have r e a f f i r m e d t h e c l a s s i c a l f o r c e - v e l o c i t y r e l a t i o n s h i p , w h i c h s t a t e s t h a t as t h e v e l o c i t y o f m u s c l e s h o r t e n i n g i n c r e a s e s t h e m u s c l e f o r c e d e c r e a s e s . Mu r r ay e t a l . (1980) s t u d i e d 72 men, f r om 20-86 y e a r s , t o d e t e r m i n e t h e i r max imal i s o m e t r i c t o r q u e and max imal c o n c e n t r i c i s o k i n e t i c t o r q u e s f o r t h e r i g h t q u a d r i c e p s and h a m s t r i n g s . I s o m e t r i c s t r e n g t h was t e s t e d a t 30°, 45° and 60°, w h i l e i s o k i n e t i c s t r e n g t h was measured a t 36°/s . G e n e r a l l y t h e i r f i n d i n g s were t h a t t h e mean maximal t o r q u e v a l u e s were h i g h e s t f o r t h e y o u n g e s t g roup o f men (20 -35 y e a r s ) and t h a t maximum s t r e n g t h d e c r e a s e d w i t h i n c r e a s i n g a g e . They a l s o f o u n d t h a t t h e mean maximum t o r q u e f o r t h e q u a d r i c e p s was g r e a t e s t a t 45°, t h a t t h e mean maximum t o r q u e f o r t h e q u a d r i c e p s f r om t h e y o u n g e s t g roup o f men was 2,227 kg-cm ( 2 1 8 . 2 N.m) and t h a t t h e h a m s t r i n g s max imal t o r q u e r anged f r om 43-61% o f t h e max imal q u a d r i c e p s t o r q u e . S t u d i e s i n w h i c h t h e s t r e n g t h o f t h e q u a d r i c e p s and h a m s t r i n g s have been d e t e r m i n e d i n young women have been c a r r i e d o u t by a t l e a s t two g roups o f i n v e s t i g a t o r s . I n t h e s e s t u d i e s t h e s u b j e c t s were n o n - a t h l e t i c f e m a l e s , as t h e i n v e s t i g a t o r s were a t t e m p t i n g t o e s t a b l i s h a b a s e - l i n e o f normal d a t a f o r t h a t p o p u l a t i o n . Wya t t and Edwards (1981) s t u d i e d 50 f e m a l e s u b j e c t s aged 25-34 y e a r s on t h e i s o k i n e t i c dynamometer a t v e l o c i t i e s o f 60°/s , 180°/s and 300°/s t o d e t e r m i n e t h e peak t o r q u e s o f t h e i r q u a d r i c e p s and h a m s t r i n g s . A t 60°/s - 103 - t h e mean peak q u a d r i c e p s t o r q u e was 79 f t - l b (107 N.m) and t h e mean peak h a m s t r i n g s t o r q u e was 56 f t - l b (76 N.m) . A t 180°/s t h e v a l u e s were 57 f t - l b (77 N.m) f o r t h e q u a d r i c e p s and 45 f t - l b (61 N.m) f o r t h e h a m s t r i n g s . A t 300°/s mean peak q u a d r i c e p s t o r q u e was 38 f t - l b (52 N.m) and mean peak h a m s t r i n g s t o r q u e was 32 f t - l b (43 N.m) . In o r d e r t o r e l a t e t o t h e f u n c t i o n a l a c t i v i t y o f w a l k i n g , t h e s e a u t h o r s recommended a v e l o c i t y between 200 and 300°/s on t h e i s o k i n e t i c dynamometer , a s t h e y have r e p o r t e d t h a t t h e knee e x t e n d s a t a v e l o c i t y o f 230°/s d u r i n g w a l k i n g . The a n g u l a r v e l o c i t y a t t h e knee d u r i n g r u n n i n g wou l d t h e r e f o r e be much h i g h e r . D i b r e z z o e t a l . (1984) s t u d i e d t h e peak t o r q u e o f t h e q u a d r i c e p s and h a m s t r i n g s i n 241 u n t r a i n e d f e m a l e s aged 18-28 y e a r s . T h e i r t e s t i n g was done a t o n l y one v e l o c i t y - 60°/s . They f ound t h e mean peak t o r q u e s t o be 94 . 47 f t - l b ( 130 N.m) f o r t h e q u a d r i c e p s and 51 . 94 f t - l b ( 71 N.m) f o r t h e h a m s t r i n g s . I n v e s t i g a t o r s have a l s o a t t e m p t e d t o d e t e r m i n e t h e r a t i o o f peak c o n c e n t r i c t o r q u e , o r s t r e n g t h , between t h e q u a d r i c e p s and h a m s t r i n g s . G o s l i n and C h a r t e r i s (1979) have s u g g e s t e d t h a t t h i s r a t i o i s speed d ependen t . They f ound t h a t a t an a n g u l a r v e l o c i t y o f 30°/s t h e q u a d r i c e p s / h a m s t r i n g s r a t i o i s 2:1 ( h a m s t r i n g s / q u a d r i c e p s o r H/Q r a t i o . 5 0 ) . M o f f r o i d e t a l . (1969) r e p o r t e d t h e same H/Q r a t i o a t 23°/s and D i b r e z z o e t a l . (1985) f o u n d t h e same r a t i o a t 60°/s . However , Wya t t and Edwards (1981) r e p o r t e d t h e r a t i o s t o be .71 a t 60°/s , .79 a t 180°/s and .85 a t 300°/s i n young f e m a l e s and .72 a t 60°/s , .78 a t 180°/s and .83 a t - 104 - 300°/s f o r young men. They c o n c l u d e d f r om t h e i r r e s u l t s t h a t t h e d i f f e r e n c e between t h e s t r e n g t h i n t h e f l e x o r s and e x t e n s o r s d e c r e a s e s as t h e v e l o c i t y i n c r e a s e s , and t h a t t h e r a t i o s a r e s i m i l a r f o r men and women i n t h e same age g r o u p , w i t h s i m i l a r l e v e l s o f a c t i v i t y , t e s t e d a t t h e same a n g u l a r v e l o c i t y . In h i s r e v i e w o f 50 r e p o r t s p e r t a i n i n g t o t h e s t r e n g t h r e l a t i o n s h i p o f t h e knee f l e x o r s and e x t e n s o r s , Nosse (1982) c o n c l u d e s t h a t t h e r e i s n o t a f i x e d s t r e n g t h r a t i o t h a t c o u l d be a p p r o p r i a t e f o r each i n d i v i d u a l unde r a l l c i r c u m s t a n c e s , w h i c h i s c o n t r a r y t o t h e g e n e r a l l y a c c e p t e d g u i d e l i n e t h a t t h e knee f l e x o r s s h o u l d be 60% as s t r o n g as t h e i p s i l a t e r a l knee e x t e n s o r s ( S c u d d e r , 1 9 8 0 ) . Even more r e c e n t l y t h a n t h e deve l opmen t o f an i s o k i n e t i c dynamometer t o s t u d y c o n c e n t r i c mus c l e a c t i v i t y , Komi (1973) r e p o r t e d t h a t he had d e s i g n e d an i s o k i n e t i c dynamometer t o r e c o r d bo t h e c c e n t r i c and c o n c e n t r i c f o r c e s . From h i s s t u d y o f f o r e a r m m u s c l e s u s i n g h i s i s o k i n e t i c dynamometer , Komi f o und t h a t as v e l o c i t y o f c o n t r a c t i o n i n c r e a s e d t h e e c c e n t r i c f o r c e i n c r e a s e d and t h e c o n c e n t r i c f o r c e d e c r e a s e d , a l s o c o n f i r m i n g t h e f o r c e - v e l o c i t y r e l a t i o n s h i p o f m u s c l e . In N o r t h A m e r i c a an i s o k i n e t i c dynamometer c a l l e d t h e K i n e t i c Commun i ca to r E x e r c i s e Sys tem (KINCOM)* has been d e v e l o p e d w h i c h measu res c o n c e n t r i c and e c c e n t r i c mus c l e power , t o r q u e , and w o r k . In a s t u d y o f t h e r e l i a b i l i t y and v a l i d i t y o f t h e KINCOM, F a r r e l l and R i c h a r d s (1986) f o c u s e d on t h r e e o f i t s p r i m a r y f u n c t i o n s : l e v e r arm p o s i t i o n , l e v e r arm v e l o c i t y , and f o r c e m e a s u r i n g s y s t e m s . They f ound t h a t t h e d i f f e r e n c e s i n t h e f o r c e measurements were 3.2% o r l e s s , t h e l e v e r arm speed was w i t h i n * Med-ex o f C anada , I n c . , C o q u i t l a m , B . C . , Canada - 105 - 1.5% o f t h e t a r g e t speed and t h e r e was no d i f f e r e n c e i n p o s i t i o n measu remen t . They c o n c l u d e d t h a t t h e d i s c r e p a n c i e s between t h e KINCOM and t h e e x t e r n a l m e a s u r i n g d e v i c e s were s m a l l enough t h a t t h e y c o u l d be due t o c a l i b r a t i o n e r r o r and we re n o t due t o i n a c c u r a c y o f t h e KINCOM. Up t o now most o f t h e i n f o r m a t i o n r e g a r d i n g dynamic m u s c l e t e s t i n g , w h i c h c l o s e l y a p p r o x i m a t e s m u s c l e a c t i o n i n f u n c t i o n a l a c t i v i t i e s , has been g a t h e r e d f r om c o n c e n t r i c m u s c l e t e s t i n g . However , i t wou l d a ppea r w i t h t h e a d v e n t o f newer i s o k i n e t i c d e v i c e s t h a t i n f o r m a t i o n r e g a r d i n g maximal m u s c l e s t r e n g t h , m u s c l e a g o n i s t / a n t a g o n i s t r e l a t i o n s h i p s and i p s i l a t e r a l and c o n t r a l a l t e r a l l i m b s t r e n g t h r e l a t i o n s h i p s may be s t u d i e d e c c e n t r i c a l l y , and e c c e n t r i c / c o n c e n t r i c r e l a t i o n s h i p s w i t h i n a m u s c l e can a l s o be i d e n t i f i e d . Mos t i m p o r t a n t t o a s t u d y o f t h e m u s c l e s a t t h e k n e e , a r e t h e m e c h a n i c a l p r o p e r t i e s o f e c c e n t r i c work because t h e knee m u s c l e s a r e p r i m a r i l y e ne r gy a b s o r b e r s t h r o u g h o u t t h e g a i t c y c l e ( W i n t e r , 1 9 8 3 ) . However , t h e r e i s a l s o c o n c e n t r i c work by bo t h t h e f l e x o r s and e x t e n s o r s d u r i n g g a i t , w h i c h must n o t be o v e r l o o k e d i f a t h o r o u g h s t u d y i s t o be made. BIBLIOGRAPHY A n d e r s o n , J . E . , e d . G r a n t ' s A t l a s o f Anatomy. V I I I E d i t i o n . W i l l i a m s and W i l k i n s C o . , B a l t i m o r e . 1 983 . Appen , E . L . , Duncan , P.W. S t r e n g t h r e l a t i o n s h i p o f t h e knee m u s c u l a t u r e : E f f e c t s o f g r a v i t y and s p o r t . J . o f O r t h o p a e d i c and S p o r t s P h y s i c a l T h e r a p y . 7: 2 3 2 - 2 3 5 . 1986 . B a s m a j i a n , J . V . R e - e d u c a t i o n o f v a s t u s m e d i a l i s : A m i s c o n c e p t i o n . A r c h i v e s o f P h y s i c a l M e d i c i n e and R e h a b i l i t a t i o n . 5 1 : 2 4 5 - 2 4 7 . 1970 . B a s m a j i a n , J . V . M u s c l e s A l i v e . IV E d i t i o n . 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