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The physiological and perceived effects of drafting on a group of highly trained distance runners Corvalán-Grössling, Veronica 1995

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THE PHYSIOLOGICAL A N D PERCEIVED EFFECTS OF DRAFTING O N A GROUP OF HIGHLY TRAINED DISTANCE RUNNERS. By VERONICA CORVALAN-GROSSLING B.Sc. (Hons.), The University of British Columbia, 1992  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR A DEGREE OF MASTER OF SCIENCE IN THE SCHOOL OF H U M A N KINETICS We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA August 1995 © Veronica Corvalan-Grdssling, 1995  In presenting  this  degree at the  thesis  in  partial fulfilment  of  University of  British Columbia,  I agree  freely available for reference copying  of  department  this or  and study.  publication of this  his  or  her  representatives.  -School Departmetit of  Honrs A O  ¥\\^&T\CS>  The University of British Columbia Vancouver, Canada  Date  DE-6 (2/88)  c c T  \<bT* . \ C f i S  that the  may be It  thesis for financial gain shall not  permission.  requirements  I further agree  thesis for scholarly purposes by  the  is  that  an  advanced  Library shall make it  permission for extensive  granted  by the  understood be  for  that  allowed without  head  of  my  copying  or  my written  ABSTRACT  This  investigation  examined  and  compared  submaximal  oxygen  consumption, carbon dioxide production, minute ventilation, and heart rate responses during indoor track running in three running configurations in a group of highly trained distance runners.  Maximal oxygen consumption  performance testing was conducted to determine at what percentage of their maximal aerobic capacity the subjects were performing at during the test trials. Oxygen consumption, carbon dioxide production, minute ventilation, and heart rate values were measured every 20 seconds during all test trials using a portable calorimeter. Following each trial, runners were asked to rate their perceived exertion using the Borg scale.  Subjects were randomly  assigned configurations and order of testing. A recovery period of 15 minutes was required between all trials.  Nine subjects were tested at 4.47 m/s in three positions, L, D I and D2. During the 4.47 m/s  trials, drafting (DI + D2) significantly  consumption (4.02 ± 0.18  reduced  oxygen  1/min leading versus 3.81 ± 0.13 1/min drafting),  and carbon dioxide production (3.74 ± 0.23 1/min leading versus 3.32 ± 0.13 1/min  drafting) (p < 0.05).  There was no significant difference in the  reduction of oxygen consumption or carbon dioxide production between running directly behind a single runner, position DI, and running behind on the inside of a triangle, position D2. Minute ventilation and heart rate were not significantly reduced during the drafting (DI + D2) trials. There was a significant reduction in the rating of perceived exertion for running behind on the inside of a triangle, position D2.  ii  A sub-group of five subjects was also tested at 5.36 m/s in two positions, L and DI.  During the 5.36 m/s trials, drafting in position D I had the same effect as  it did at the 4.47 m/s with the exception that the reductions were slightly larger than those observed for the slower pace.  Drafting in position DI  substantially reduced oxygen consumption (4.76 ± 0.20 1/min leading versus 4.35 ± 0.20 1/min DI), and carbon dioxide production (4.44 ± 0.28 1/min leading versus 4.16 ± 0.26 L/min DI). Minute ventilation, heart rate, and rating of perceived exertion were not reduced during the drafting (DI) trials.  These results demonstrate that running within the aerodynamic shadow of another runner is very advantageous for distance runners.  Both drafting  positions tested were found to be equally effective in conserving Drafting on the inside of a triangle was the position of choice.  energy. Coaches  should expose athletes to drafting situations in training so that athletes can successfully employ this energy-saving strategy. One must also be aware that athletes who consistently run within a pack or drafting are not obtaining the full benefits of their training regimen.  iii  TABLE OF CONTENTS  Abstract  11  Table of Contents  iv  List of Figures  vi  Acknowledgment  viii  Dedication  ix  CHAPTER ONE Introduction  1  Statement of the Problem  12  Significance of the Study  13  Delimitations  14  Limitations  15  Assumptions  16  CHAPTER TWO Literature Review  17  Hypotheses  26  CHAPTER THREE Methods and Procedures  27  CHAPTER FOUR Results  38  C H A P T E R FIVE Discussion  48  iv  Conclusion and Recommendations  61  Bibliography  63  Appendix 1: Definition of Terms  70  Appendix 2: Case Study  72  Appendix 3: Pilot Study  81  v  LIST OF FIGURES Figure 1  The energy demands of distance running . (modified from Fox et al. 1993)  2  Figure 2  A proposed mechanism for i m p r o v e d performance times based on alterations i n r u n n i n g strategies a n d their effects on running economy.  5  Figure 3  Laminar and turbulent air flow around a runner.  7  Figure 4  A i r flow around runner.  drafting behind another  11  Dynamic pressure measurements at various distances around a runner i n the presence of 6 m / s w i n d , (from P u g h et al. 1976)  20  Oxygen consumption response to r u n n i n g i n leading and drafting positions. (from Corvalan-Grossling et al. 1994)  24  M i n u t e ventilation response to r u n n i n g i n leading a n d drafting positions. (from Corvalan-Grossling et al. 1994)  24  Table 1  Phase I: Subject Characteristics  30  Table 2  Phase II: Subject Characteristics  30  Figure 8  Drafting Configurations  35  Table 3  Phase I: Physiological responses to different positions.  running  39  Figure 9  Phase I: Percent reduction i n physiological parameters as a result of drafting i n positions D I and D2.  40  Table 4  Phase II: Physiological responses to different positions while running at 4.47 and 5.36 m / s .  running  42  Figure 10  Phase II: Percent reduction i n physiological parameters as a result of drafting i n position D I at 4.47 and 5.36 m / s .  43  Table 5  MANOVA  44  Figure 5  Figure 6  Figure 7  a runner  Summary  vi  Table 6  Survey Results  46  Figure A l  Diagram of Cosmed K 2 telemetry unit.  75  Figure A 2  Heart rate response to running i n leading and drafting positions.  77  Figure A 3  Oxygen consumption response to r u n n i n g i n leading and drafting positions.  78  Figure A 4  M i n u t e ventilation response to running i n leading and drafting positions.  79  Table A l  Subject characteristics.  88  Figure A 5  Drafting configurations.  92  Figure A 6  Percent reduction i n physiological parameters as a result of drafting i n position D I .  94  Table A 2  Means of physiological parameters for leading drafting positions one minute post-exercise.  and  95  Table A 3  Physiological parameters for additional positions one minute post-exercise.  drafting  96  vii  A C K N O W L E D G M E N T  I w o u l d like to give m y sincere appreciation and gratitude to m y thesis committee: Dr. D o u g Clement, Dr. K e n Coutts, Dr. D o n M c K e n z i e , and especially to my advisor and thesis committee chairman, Dr. Jack T a u n t o n , for his guidance, support, encouragement, and enthusiasm throughout m y graduate studies program. I w o u l d like to give m y sincere appreciation and gratitude to the subjects and volunteers w h o m devoted their time and energy to make this study possible: H a m z a A b a d i , Scott Bartlett, M a r k Bates, Robin Beynor, Shane B i l o d e a u , Brendon Brazier, Peter Cardie, Terry Cardie, D a n Chan, M e g D e C o r v a l a n , Wayne Evans, Stephane Gange Chris Johnson, Steve M c M u r d o , R a n d y M o o d y , John Oech, A n m a r Ougja, Ryan Press, M a l c o l m Smillee, Edward Smith, Cliff Storlund, A n d r e w Tovinen, Scott Vanderberg, Steve Walters, Peter Weisinger, Sue W o o d . I w o u l d especially like to thank the roller bladders: John Lyotier, Scott Bartlett, and D o u g Geddes. I w o u l d like to express m y gratitude to M a r k Smith, the president of AeroSport ( A n n Arbor, Michigan), w h o generously entrusted me w i t h the T E E M 100. I w o u l d like to express my gratitude to B i l l Hodgsen of Brathwaites Oliver Medical Inc., w h o generously entrusted me w i t h a portable pulse oximeter and carbon dioxide analyzer; and John Sanker of the Physiology Department at U B C , w h o entrusted me w i t h the back-up system. I w o u l d like to express my gratitude to the technical assistance of L i n d a S m i t h of AeroSport (USA), Dianna Jesperson of the A l l a n M c G a v i n Sports M e d i c i n e Centre, and Bob Frid of the School of H u m a n Kinetics at U B C . I w o u l d like to thank Corrine Johnston of the Pacific National Exhibition, and Dr. Nestor Korchinsky of the School of H u m a n Kinetics for all their assistance at the ShowMart and B C Place. I w o u l d like to thank Athletics Canada and the team coaches: Dr. D o u g Clement, Marek Jedrzejek, Jerry Tigh, and John H i l l , for all their support and generous cooperation. I w o u l d also like to thank m y encouragement, and inspiration.  parents  VCG  viii  for  a  lifetime  of  support,  DEDICATION  To Dr. Jack Taunton  CHAPTER ONE INTRODUCTION  Distance Runners The contributions of metabolic, physical, and mechanical variables to running performance are a function of distance and intensity. Maximal aerobic capacity (VC>2max)/ submaximal oxygen consumption (V02), and lactate threshold are metabolic variables that increase in importance as distance increases.  In any  endurance running event, optimum performance is generally achieved by efficiently utilizing the available energy. The longer the distance of the run, the more important the conservation of energy becomes. Having a high capacity for providing the exercising muscles with energy is critical, as is being able to maintain a high running speed without negatively affecting the rate of utilization of total energy sources. Figure 1 shows the relative demands placed on the athlete's anaerobic and aerobic energy system in relation to race distance.  Long distance runners (5 km or greater) have been characterized as having higher maximal aerobic capacities, using oxygen more efficiently, and having significantly lower lactate accumulations than middle distance runners (Butts 1985).  A t the elite level these athletes have optimized most aspects of their  running mechanics. Their general movement sequences are similar, and they tend to use running strides that are near their optimum, the most relaxing stride which does not reduce momentum (Grabiner 1993).  Long distance runners  generally run at a constant pace throughout most of a race. Race velocities range from 4.5 to 6.5 m / s (Adrian et al. 1989, Foster et al. 1994).  1  QJ 3 bJD O  bJD u >^ Q J J H  Q J  • Aerobic  a, a3 Q J  E3 Anaerobic  <4H  .S o X  Tl  ell  Distance (m)  FIGURE 1:  The energy demands of distance running, (modified from Fox et al. 1993)  2  Running Economy and Performance I n track a n d f i e l d h o w specific b i o m e c h a n i c a l , p h y s i o l o g i c a l , p s y c h o l o g i c a l , or e n v i r o n m e n t a l v a r i a t i o n s relate to the p e r f o r m a n c e a b i l i t y of r u n n e r s  are  c o n t i n u a l l y b e i n g assessed. There is a constant quest i n athletics to f i n d a n aspect of r u n n i n g that c a n i m p r o v e p e r f o r m a n c e t i m e s .  However, using running  p e r f o r m a n c e as a c r i t e r i o n for the effects of a p a r t i c u l a r factor c a n be c o n f o u n d e d b y the m a n y factors a f f e c t i n g p e r f o r m a n c e  including r u n n i n g mechanics,  p h y s i o l o g i c a l state, p s y c h o l o g i c a l factors, a n d race strategy. A n alternative is to l o o k at r u n n i n g e c o n o m y .  R u n n i n g e c o n o m y is d e f i n e d as s u b m a x i m a l  m e t a b o l i c e n e r g y e x p e n d i t u r e a n d g e n e r a l l y refers to the aerobic d e m a n d of a p a r t i c u l a r r u n n i n g speed ( M o r g a n et a l . 1990). T h e changes i n aerobic d e m a n d at a particular  r u n n i n g s p e e d c a n be u s e d to i n v e s t i g a t e the d i f f e r e n c e s i n  m e t a b o l i s m w h i c h m a y exist u n d e r different c o n d i t i o n s or i n different p e o p l e .  M a x i m a l aerobic c a p a c i t y a n d r u n n i n g p e r f o r m a n c e h a v e b e e n s h o w n to be s t r o n g l y related w h e n e x a m i n i n g a large p o p u l a t i o n of distance r u n n e r s w i t h a variety of performance levels.  H o w e v e r , the c o r r e l a t i o n b e t w e e n m a x i m a l  aerobic capacity a n d performance a m o n g h i g h l y trained a n d  experienced  distance r u n n e r s is m u c h l o w e r . T h i s is not s u r p r i s i n g c o n s i d e r i n g they c o m p r i s e a v e r y h o m o g e n e o u s g r o u p of c o m p a r a b l e a b i l i t y a n d s i m i l a r m a x i m a l aerobic capacities ( C o n l e y et a l . 1980). T h e r e is a clear i n d i c a t i o n i n the literature that r u n n i n g e c o n o m y c a n be a n i m p o r t a n t factor i n p e r f o r m a n c e e s p e c i a l l y at the elite l e v e l ( C o s t i l l et a l . 1973). R u n n i n g e c o n o m y v a r i e s c o n s i d e r a b l y a m o n g h i g h l y t r a i n e d runners, a n d has b e e n f o u n d to account for a large a m o u n t of the v a r i a t i o n o b s e r v e d i n p e r f o r m a n c e of this s u b g r o u p ( C a v a n a g h 1990, C o n l e y et a l . 1980, D a n i e l s 1985).  O t h e r factors w h i c h a c c o u n t for the v a r i a t i o n i n  p e r f o r m a n c e to a lesser extent i n c l u d e m u s c l e fiber c o m p o s i t i o n , a n a e r o b i c  3  threshold, peak muscle and b l o o d lactate tolerance, biomechanics, and psychological factors.  Reducing oxygen consumption by optimizing running mechanics or changing racing strategies can i m p r o v e performance b y increasing the m a x i m u m sustainable speed. The advantages of w o r k i n g at a lower oxygen consumption rate are that the demands on the oxygen transport system are decreased and that the depletion of energy sources such as glycogen are reduced, delaying the onset of fatigue. This gives athletes the ability to increase their m a x i m u m sustainable speed and improve their performance times (see Figure 2).  Even reductions in  oxygen consumption as small as a percent or two could lead to meaningful improvements in performance times (Cavanagh 1990, Grabinger 1993, Williams 1985). Cavanagh (1990) suggests that a 2 % improvement translates into a 2.5 minute improvement in elite marathon race performance. Running economy has been shown to be limited by several intrinsic factors such as an athlete's age, weight, biomechanics, state of fitness and fatigue, as w e l l as extrinsic environmental factors such as altitude, temperature, r u n n i n g surface, and aerodynamic drag (Daniels 1985).  Aerodynamics and R u n n i n g A i r resistance is a major source of energy expenditure i n many  sports,  particularly d o w n h i l l skiing, ski jumping, the luge, bobsledding, speed skating, and cycling, where high velocities are reached (Halliday et al. 1988, H i l l 1928, K y l e et al. 1984, d i Prampero et al. 1976). Thus, efforts to reduce aerodynamic drag result i n decreased energy cost. A i r resistance is estimated to cost distance runners between 2-8% of their total energy (Davies 1980, H i l l 1928, P u g h 1970,  4  Original Maximal Sustainable Speed 9 0 % V 0 2 m a x at 6  m/s  Change Race Strategy Decreased Energy Cost Improved Running Economy  Decreased V O 2 8 8 % V 0 2 m a x at 6  m/s  Increased Maximum Sustainable Speed 9 0 % V 0 2 m a x at 6 . 1 3  m/s  Improved Performance Times  F I G U R E 2:  A proposed mechanism for improved performance times based on alterations i n r u n n i n g strategies and their effects on r u n n i n g economy.  5  Pugh 1971). The energy cost of running at a constant velocity increases as wind resistance increases (Costill 1979).  Aerodynamic drag occurs for two reasons. One, the pressure that results from air molecules striking a surface and bouncing off, undergoing momentum changes and exerting normal forces on the surface. The other type of force, air friction, arises from the sliding motion of air molecules along the surface as they collide with rough surfaces.  Fluid flow can be either laminar or turbulent,  depending on many factors such as speed, surface roughness, and the type of surface material (Halliday et al. 1988, Olsen et al. 1987, Whitt 1982). A t slow speeds the flow of air molecules will be laminar, this results in quite low drag forces. A s the relative speed of the air and the surface increase, the laminar flow becomes unstable and layers of air begin to separate.  The flow then becomes  turbulent, characterized by whirling eddies of air (see Figure 3). boundary layers have much higher drag than laminar layers.  Turbulent  However, the  highest drag is caused by instability at air velocities in the transition region between laminar and turbulent flow (Birkhoff 1960, Halliday 1988).  The  aerodynamic drag can be five times greater in the transition speed ranges than the aerodynamic drag for the purely turbulent flow. Therefore, it follows that to achieve low drag forces this transition region must be avoided. The transition region has been estimated to occur at speeds of about 4 m / s to 6 m / s for a cyclist (Tipler 1990). Considering the similarities in geometry and drag coefficients between  cyclists and runners (Pugh 1976), the transition region w o u l d  theoretically occur at the same speed range of 4-6 m / s for runners. coincides with long distance racing paces.  6  This  -„  Laminar Flow  Turbulent Flow  F I G U R E 3:  Laminar and turbulent air flow around a runner. moving right is simulated here by a filled circle.  7  The runner,  The relative velocity of the air on the track or road is rarely zero. When running in a tail wind, the aerodynamic drag will provide a forward force. A head wind, on the other hand, provides a retarding force as it increases the aerodynamic drag. It has been estimated by Dapena et al. (1987) that a 2 m / s tail wind can give a 100 m sprinter a 0.07 second advantage; while, a 2 m / s head wind can result in a 0.085 second disadvantage. It appears that the hindrance produced by a head wind is larger than the time aid produced by a tail wind of the same intensity. Quantitatively, drag forces retarding forward motion are characterized by the equation: F D = 0 . 5 C D d A V . Where F D is the drag force, C D is the drag 2  coefficient, d is the air density, A is the projected frontal area of the runner, and v is the relative velocity of the air and the surface over which the air is flowing. This equation includes both air friction and pressure effects. However, it is only an estimate. The drag coefficient cannot be calculated for most real objects and is usually inferred from experimental data obtained from measurements made in wind tunnels.  Aerodynamic drag can be affected by changing any of the above variables. For example, air density which is relatively constant at a given location, changes with altitude. A t 1.6 km above sea level air density is reduced by 10 %, thus reducing aerodynamic drag by 10 %. A t first glance it seems possible that performance would improve at altitude due to the decrease in air resistance, however, this is not the case in endurance events. A n y reduction in energy cost is cancelled and surpassed largely as a result of increased ventilatory cost in response to acute hypoxia (Daniels et al. 1970, Hagerman et al. 1975). Altitude is not the only environmental factor that influences air density; higher temperature and, to a lesser extent, humidity can also affect air density. A i r density at 20 ° C is 1.205 kg/m  3  and at 40 ° C drops to 1.128 k g / m . A 5 ° C increase in air temperature 3  8  produces a 1.5 % reduction i n aerodynamic drag. Selecting a location w i t h a higher temperature may not be an appropriate strategy to decrease the energy costs of overcoming aerodynamic drag forces, other physiological responses to higher temperatures must also be considered. A l t h o u g h an increase i n body temperature improves muscle efficiency, it simultaneously increases the cost of circulation, ventilation, and sweating thus increasing oxygen consumption. The effects of humidity on air density are not as large as for altitude or temperature. D r y air at 30 °C and 1 atm has a density of 1.165 k g / m ; at the same temperature 3  and pressure air completely saturated i n water vapor has a density of 1.146 kg/m . 3  Selecting a high altitude location w i t h high humidity theoretically could  have an appreciable effect on performance but only i n sports such as sprinting and speed cycling where there is insufficient time for the physiological responses to these environmental conditions to adversely affect performance.  R e d u c i n g frontal area and thus exposure to aerodynamic drag is easily accomplished by athletes i n other sports.  Cyclists lean forward until their backs  are horizontal and their arms are tucked tightly against their bodies. Skiers can crouch d o w n over their skis into the "egg" position until they are practically sitting on their ankles. Speed-skaters bend their upper bodies 90 degrees so they are parallel to the ground. Runners are limited in their postural adjustments but can decrease their frontal area by using tight fitting clothing and by trimming or covering their hair.  Typical strategies employed by runners to reduce their  aerodynamic drag are to reduce their coefficient of drag by using smooth spandex cloth, modified shoes, and head gear. W i n d tunnel tests of clothing, hair, and shoes show that it is possible to reduce the aerodynamic drag of a runner by 0.5 % to over 6 % (Adrian et al. 1989, Kyle et al. 1986). Another means of reducing aerodynamic drag is by decreasing the drag coefficient. Streamlining  9  is a common technique employed in bicycle design.  Race bicycles are being  designed so that the laminar air flow is preserved during the ride (Halliday et al. 1988, Kyle et al. 1984).  A strategy that could reduce the aerodynamic drag forces on runners is drafting (see Figure 4). This technique is commonly applied in cycling, skiing, and other high drag sports. Many investigators and runners have recommended the tactic of running in the aerodynamic shadow of another runner, primarily based on anecdotal information and the results obtained from investigations on the effects of drafting in other sports (Higdon 1978, H i l l 1928, Kyle 1979, Kyle 1979a). Only two studies have investigated this topic, but only one has been conducted on a runner (Pugh 1971). To date, the effects of drafting and running have only been cursorily examined.  Further research is needed to quantitate the benefits of  drafting in distance running.  10  F I G U R E 4:  A i r flow around a runner drafting behind another runner. runners, moving right, are simulated here by filled circles.  11  The  S T A T E M E N T OF THE P R O B L E M  General Purpose Statement To investigate h o w drafting, i n various positions, affects specific physiological and perceptual variables of a group of highly trained elite level distance runners' in a track environment. This study w i l l investigate the following questions:  a)  Does drafting reduce the physiological variables: oxygen consumption, carbon dioxide production, minute ventilation and heart rate? b) Does drafting reduce the rate of perceived exertion?  c) Do the effects of drafting, if any, affect the  physiological variables differently at different speeds in the range of 4-6 m / s ? d) Do the effects of drafting, if any, affect the rate of perceived exertion differently at different speeds i n the range of 4-6 m / s ? e) Do different drafting positions, running behind a single runner or a group of runners, affect the physiological variables differently? f) D o different drafting positions, running behind a single runner or a group of runners, affect the rate of perceived exertion differently? g) Which running position do elite distance runners, as represented i n this group of subjects, find the most beneficial i.e. energy saving, less constricting, comfortable, and applicable as race strategy?  12  more  S I G N I F I C A N C E OF T H E S T U D Y  This study will provide the first values on oxygen consumption, carbon dioxide production, minute ventilation, heart rate, and rate of perceived exertion while drafting in the track environment. The practical implications are numerous: If findings are positive, athletes will be justified in using drafting as a means to conserve energy and then increase the maximal sustainable speed at the end of a race. Moreover, training methods will have to be reevaluated, since the front runners in a pack would be getting different benefits than drafters during each training session. By determining which positions result in the greatest reduction of air resistance, distance runners will be able to integrate this knowledge into their racing strategies. The findings of this study may shift the way races are run. For example, a team of runners could run at a record pace and maintain it by rotating the runners at the front, while shielding the ultimate  winning  individual, and the winning runner could easily be able to improve on his best time. A n individual runner could run in the aerodynamic shadow of another runner, not only saving energy, but also putting psychological pressure on his competitor. A t a strategic point in the race, the drafting runner could break away at a higher sustainable speed.  13  DELIMITATIONS  The study was delimited by: 1. The subject sample size, 2. The sample type (highly trained to elite level male distance runners), 3. The range of running speeds being tested (4.47 m / s and 5.36 m / s ) , 4. The number of positions being tested (3), 5. The testing period (three weeks), 6. The duration of each testing session (1-4 hours), 7. The recovery time between each trial (15 minutes), 8. The testing site (an indoor 200 m flat unbanked wooden oval track).  14  LIMITATIONS  The results of this study were limited by: 1. The data collection capabilities and accuracy of the AeroSport Teem 100 and C P X - D gas analyzers, 2. The experimental conditions and the inability to control temperature and humidity for the comfort of the subjects during testing, 3. The subjects' ability and motivation to perform maximally to exhaustion during the treadmill V02max test, 4. The subjects' metabolic and psychological responses to the protocols of the study, 5. The speeds selected to test subjects, w h i c h may differ from their typical race paces, 6. The effects of training and competitions during the testing period, 7. The effects repetitive exposure to the testing protocol, 8. The choice of dependent variables.  15  ASSUMPTIONS  1. The subjects' measured VC>2max values were a true reflection of their maximal aerobic capacity. 2. The subjects were capable of running for a m a x i m u m of 10 minutes at a steady-state of exercise at the experimental speeds. 3. The training sessions aimed to familiarize subjects w i t h the equipment, environmental test conditions, and drafting configurations were adequate. 4. A runner w h o was economical at a given speed of running w o u l d also be economical at other speeds. 5. Subjects had optimized most aspects of their r u n n i n g mechanics prior to participating i n the study. 6. Subjects were capable of running at a speed higher then the one they were tested at for a m i n i m u m of 10 minutes. 7. A reduction i n energy costs, decrease i n oxygen consumption and carbon dioxide production, throughout a range of submaximal speeds of running w o u l d result i n an improved performance time. 8. A prolonged maximal run (a race) w o u l d not produce an increase i n aerobic demand of running or disrupt the gait pattern i n subsequent short-term, submaximal runs (experimental trials). 9. Measures of oxygen consumption, carbon dioxide p r o d u c t i o n , minute ventilation, and heart rate i n highly trained male runners remained stable across the two testing sessions. 10. The runners were i n a relatively steady-state condition, and that anaerobic sources contributed only minimally to the total energy expenditure and that minimal variations i n substrate utilization occurred during the tests.  16  CHAPTER TWO LITERATURE REVIEW  A . V . H i l l (1928) w a s one of the first to investigate the q u e s t i o n of air resistance o n runners. man  H e m e a s u r e d the p r e s s u r e e x e r t e d o n a n 8 - i n c h m o d e l of a r u n n i n g  at v a r i o u s air velocities i n a 3-foot w i n d - c h a n n e l . H i l l p r o d u c e d a n e q u a t i o n  for the force exerted o n a r u n n e r i n terms of air d e n s i t y , the projected area of the r u n n e r , a n d the v e l o c i t y . F r o m h i s results he estimated that i n s t i l l air 3-5% of the t o t a l e n e r g y r e q u i r e m e n t of a r u n n e r w o u l d be u t i l i z e d to o v e r c o m e air resistance.  P u g h (1970) e s t i m a t e d the f r a c t i o n of the total e n e r g y cost of track  r u n n i n g r e q u i r e d to o v e r c o m e air resistance o n the track to be about 13 % w h e n r u n n i n g at a s p r i n t v e l o c i t y of 10 m / s , a n d 8% w h e n r u n n i n g at a m i d d l e d i s t a n c e v e l o c i t y of 6 m / s .  S i m i l a r l y , D a v i e s (1980) e s t i m a t e d that the t o t a l  energy cost of o v e r c o m i n g air resistance o n a c a l m d a y w o u l d be 7.8 % at 10 m / s , 4 % at 6 m / s , a n d 2 % at 5.0 m / s .  A s a result of these f i n d i n g s , the focus of  research has shifted to d e t e r m i n i n g at w h i c h v e l o c i t i e s air resistance b e g i n s to affect p e r f o r m a n c e a n d to r e d u c i n g the a e r o d y n a m i c d r a g forces e x e r t e d o n runners.  M a k s u d et a l . (1971) f o u n d that at r u n n i n g speeds of 4.47 m / s a n d 5.36 m / s o x y g e n u p t a k e w a s s i g n i f i c a n t l y h i g h e r d u r i n g track r u n s w h e n c o m p a r e d to t r e a d m i l l r u n s , b u t that there w e r e n o s i g n i f i c a n t differences b e t w e e n the t w o at the r u n n i n g s p e e d of 3.13 m / s . A d d i t i o n a l e v i d e n c e i n d i c a t i n g that the effect of air resistance o n r u n n i n g e c o n o m y p r o g r e s s i v e l y b e c o m e s greater as r u n n i n g s p e e d increases has b e e n p r o v i d e d b y M c M i k e n et a l . (1976) a n d D a n i e l s et a l . (1985).  M c M i k e n et a l . (1976) f o u n d n o s i g n i f i c a n t differences i n r u n n i n g  17  economy until the running speeds of 4.33 m / s where reached. Daniels et al. (1985) reported that track running did result in higher aerobic demands at speeds above 4.47 m / s . From these three studies, it is clear that the drag forces play a significant role at speeds greater that 4.47 m/s. The regression equations derived from these studies are often used now to equate treadmill results to the track experience.  Considering that at the critical velocity range between 4-6 m / s , the estimated transition region between laminar and turbulent air flow and speeds at which elite distance runners compete in, it is possible that the energy expenditure and therefore running economy are markedly altered by the aerodynamic drag forces which an athlete encounters. It is surprising that there has been very little work on drafting and drafting configurations for distance runners.  Pugh (1971)  examined what would happen to the running economy when a runner drafted behind another runner. In this single case study, Pugh measured the oxygen consumption of an international middle and long-distance athlete while running on a treadmill at 4.46 m / s against varying w i n d velocities. H e found that drafting, running about 1 m behind another runner, in calm air reduced this athlete's oxygen consumption by 0.15 L / m i n (4.8 %); while, drafting virtually eliminated air resistance and reduced this athlete's oxygen consumption by 0.25 1/min (6.5 %), when running against a 6 m / s wind. This is approximately an 80% reduction in the energy cost of overcoming air resistance.  Pugh then  measured the dynamic air pressure around the runner with a Pitostatic tube.  18  The pressure was negative 0.6 m behind the runner and still relatively low 1 m behind the runner. A t the positions slightly to the side-behind the runner, the pressures were almost the same as the pressure 2 m in front of the runner. Pugh's pressure measurements are shown in Figure 5. The fact that running economy improved in this case study suggests that drafting could be a useful technique to evade aerodynamic drag. Moreover, the pressure results are useful for determining which drafting positions may be most effective.  They suggest  that drafting directly behind a runner may be more effective than drafting behind a competitors shoulder.  The only additional evidence available in the running literature that indicates that drafting can reduce a runner's aerodynamic drag is found in a study conducted on cyclists by Kyle (1979). Based on his results on cyclists coasting in a 200 m hallway, Margaria's data (1963) for the rate of energy consumed during running in still air, and the assumption that drag coefficient for the upright position in cycling was equivalent to that of runners, Kyle predicted that drafting would improve running economy by 4 % when drafting 1 m behind another runner at 6 m/s. Although this value has meaningful practical implications, it is slightly lower than that obtained by Pugh (1971).  Methodological and  computational differences could account for the discrepancy. However, another reason for the difference may result from the assumption made on the value of the coefficient of drag.  The values estimated by other investigators differ  considerably from those used by Kyle (Pugh 1976, Shanebrook et al. 1976).  19  120  r  90  -  60  -  +2.25  Front  30 0  -  -30  -  ^Runner^)  •+2.05 (91%)  -60  +2.15(96%)  •+0.25(11%)  +0.45 (20%)  • • • •  -90  +0.05 (2%) -0.05 (-2%) +0.05 (2%) +0.15 (7%)  -120 -80  -60  -40  -20  0  20  40  60  80  Distance (cm)  F I G U R E 5:  D y n a m i c air pressure i n k g f / m at various distances from a runner. Observations at a height of 126 cm and w i n d speed 6 m / s . Percentage reduction of air pressure is shown i n parenthesis (from Pugh 1976). 2  20  The majority of the research on drafting's effects on aerodynamic drag, energy expenditure, and performance has been conducted on cyclists, but it yields useful information. In Kyle's (1979) investigation on the effects of drafting on cycling power output and wind resistance in a variety of positions, he found that drafting directly behind another rider reduced the air resistance by 44 % irrespective of the number of riders in the pace line. When a rider drafted in the center of a tightly packed cluster of riders the air resistance was surprisingly only reduced by 24 %; however, this effect was investigated in a single test. Kyle also reported that air resistance was only reduced by 23 % when the rider drafted in a position slightly to the side-behind instead of directly behind another rider. A s would be expected from Pugh (1971) and Shanebrook et al. (1976) pressure data, he found the reduction in air resistance increased the closer a rider drafted behind another rider. McCole et al. (1990) conducted a similar study to Kyle's. They measured energy expenditure, oxygen consumption, of competitive cyclists on a flat stretch of straight road while drafting. They reported an 18 % reduction in oxygen consumption at 8.89 m / s and a 27 % reduction in oxygen consumption at 10.28 -11.11 m / s for subjects drafting behind one rider. Drafting 1, 2, 3, or 4 riders in a line resulted in the same reduction of oxygen consumption, while drafting a group of 8 riders at 11.11 m / s reduced oxygen consumption by 39 %. The latter results on the effect of drafting behind a pack of riders conflicts with Kyle's (1979) observation, demonstrating the need to have multiple subjects and trials in these investigations.  The relevance of these studies on cyclists lies in the configuration portion (Kyle 1979, McCole et al. 1990). They indicate that drafting behind a single runner may significantly increase running economy, and that the drafting behind a pack on a straight track may improve running economy even more.  21  Drafting behind a  pack may turn out to improve running economy even more than running behind a single runner, but this position poses other strategic problems for runners. This position may conserve energy and be beneficial physiologically, but strategically a runner is at a disadvantage when boxed in.  The effects of drafting has been studied extensively in other sports where high drag forces must be overcome. In swimming, drafting has been found to reduce post-exercise oxygen consumption by 11%, blood lactate by 31%, and rating of perceived exertion by 21% (Basset et al. 1991). In cross-country skiing, Bilodeau et al. (1994) found that drafting significantly reduced heart rate by 5.6%, from 163 to 154 beats/min.  While in kayaking, a similar technique of wash riding has  been found to produce an 11% reduction in the energy cost of paddling (Gray 1992). In track & field, little has been done to quantify drafting's effects, mostly because of the difficulty in measuring oxygen consumption while running outdoors and in drafting configurations. These measurements are now possible with the development of two portable gas analyzers the Cosmed K2 (Rome, Italy) which has been found to be a reliable and valid instrument for measuring oxygen consumption, minute ventilation, and heart rate (Bishop et al. 1995, Crandall et al. 1994, Lucia et al. 1993), and the AeroSport Teem 100 (Ann Arbor, Michigan, U.S.A.) which has been found to be a reliable and valid instrument for measuring oxygen consumption, minute ventilation, heart rate, as well as, carbon dioxide production (Novitsky et al. 1995, Segal et al. 1994, Segal et al. 1995).  22  Two preliminary investigations have been conducted by Corvalan-Grossling et al. .  In the first, a case study, the metabolic responses of an elite level distance  runner to drafting outdoors in calm air were examined using the Cosmed K2. Corvalan-Grossling et al. (1994) found that drafting at the running speed of 4.47 m / s substantially reduced this athlete's oxygen consumption 0.72 1/min (29.0 %) and minute ventilation 20.6 1/min (18.7 %).  Heart rate  was only reduced 8  beats/min (5 %), while the subject rating of perceived exertion remained the same.  The reductions in oxygen consumption and minute ventilation were  observed to continue for at least the first two minutes of recovery as shown in Figures 6 and 7.  The constraints imposed by the Cosmed K2 may have  influenced these results. The face mask could possibly have altered this subject's breathing pattern as suggested by Loring et al. work (1990).  In the subsequent pilot study conducted by Corvalan-Grossling et al. (1995), testing was conducted indoors on a oval concrete corridor to have greater control over the environmental conditions.  Less constricting test apparatus was also  used to minimize the confounding effects which the equipment could produce on subjects respiration and heart rate.  In this study, the metabolic responses to  drafting at the running speed of 4.47 m / s was studied in eight highly trained male distance runners. Drafting was found to significantly reduce one minute post-exercise oxygen consumption 0.24 1/min (15 %), carbon dioxide production 0.31 1/min (22 %), and minute ventilation 8.6 1/min (17 %).  The rating of  perceived exertion went d o w n by one point, while heart rate was  not  significantly reduced. One minute post-exercise measurements have been made in previous studies to gauge the effects of drafting and maximal oxygen  23  / Recovery  3  o  2.5 2  3  mm ii i i  o S 1.5  u  ci  \  1  ^  1  nil 1111111111 im 11 in iiiiiiHiii  OH  l niiTininiiMim II II i i i i i i i  ND DI  60 X  0.5  O  0 o o o  o  o  o  o  CO  O T-H  CO r-H  O CO CN CN  o  o  o o CO  o  CO CO  o o  o  CO  o o  o  CO  o o  o CO  M5  o O  o  CO  t>!  o o  OO  TIME (sec)  FIGURE 6:  Oxygen consumption response to leading and drafting running positions, (from Corvalan-Grossling et al. 1994)  o o o o o o o o o o o o o o o o o o c ^ o c f ) o c n o c ^ o e ^ o c ^ o c o o ^ o T I M E (sec)  FIGURE 7:  Minute ventilation response to leading and drafting running positions, (from Corvalan-Grossling et al. 1994)  24  consumption in swimmers and speed skaters (Basset et al. 1991, Brehm et al. 1986, Costill et al. 1985, Costill et al. 1991, Lavoie et al. 1983, Montpetit et al. 1981, di Prampero et al. 1976). However, measurements made during an activity are the most precise means of evaluating the physiological state of an athlete during that activity.  Research is needed to determine which configurations improve  running economy and are the most practical for distance runners to implement in competition; moreover, the question of how much drafting improves running economy in distance running still remains unclear.  25  HYPOTHESES  1. Submaximal oxygen consumption w i l l be lower while running on a treadmill than while running on a windless flat unbanked wooden oval track (p< 0.05).  2. The p h y s i o l o g i c a l variables: s u b m a x i m a l oxygen consumption, carbon dioxide production, minute ventilation and heart rate, w i l l be reduced during the drafting trials (p< 0.05).  3. The different drafting positions w i l l affect the p h y s i o l o g i c a l variables differently (p<0.05). Drafting behind a group of shield runners w i l l reduce the physiological variables more than drafting directly behind a single shield runner.  4. The rating of perceived exertion w i l l be reduced during the drafting trials (p< 0.05).  5. Both drafting behind a single shield and drafting behind a group of shield runners w i l l reduce the rating of perceived exertion (p<0.05).  26  CHAPTER  THREE  METHODS  OBJECTIVES  The purpose of this study was to investigate h o w drafting, r u n n i n g i n the aerodynamic shadow of another runner, affected specific physiological variables w h i c h are highly correlated to performance (Bunc et al. 1988, Costill et al. 1973, Daniels 1985, Schoeller et al. 1990, Steed et al. 1994). These variables included: s u b m a x i m a l o x y g e n c o n s u m p t i o n , carbon d i o x i d e p r o d u c t i o n ,  minute  ventilation, and heart rate. O p t i m i z i n g r u n n i n g economy can i m p r o v e performance by increasing the m a x i m u m sustainable speed; thus, if drafting reduces oxygen consumption, minute ventilation, and heart rate, it is more than likely to improve performance.  In order to determine the optimal position for runners during a race, one leading position and two drafting positions were tested. Runners were also questioned as to w h i c h positions they found to be the most beneficial. Runners' perceived exertion was also measured i n order to examine if drafting reduced the rate of perceived exertion. The study was composed of two experimental tests, and one maximal aerobic power test. The protocols followed for both portions of the study are described below.  SUBJECTS  A total of twelve h i g h l y trained and experienced male distance  runners  volunteered to participate i n this investigation. Ten of the twelve athletes were internationally competitive senior members of local running clubs. Three of these athletes were also internationally competitive triathletes. One athlete was a  27  former competitive distance runner, while another athlete was a former competitive swimmer / n o w marathoner.  By self-report, all subjects were  competing in distance events ranging from 5 km to marathon distances, were actively training in excess of 40 km of distance running a week for at least one year, had completed a mile run in a time of 5 minutes or less within 2 months of their participation in the study, and were apparently healthy with no muscloskeletal complaints or documented history of cardiorespiratory disease. At the time of testing, all subjects were free of musculoskeletal complaints. A l l subjects were fully informed of the risks and potential discomfort associated with the testing procedures before giving their signed informed consent as required by the Behavioral Sciences Screening Committee for Research Involving H u m a n Subjects at The University of British Columbia.  A l l subjects provided health  background information and underwent a medical screening and clearance by their coaches, as well as, a physician acquainted with the process and with the specific protocol that was employed.  Nine athletes completed all portions of phase I. A subgroup of five athletes participated in phase II. Due to the limited availability of test site, equipment and most importantly subjects and shield runners, it was impossible to test all the athletes at the two paces in the three different positions*  Optimal sample  size of nine was determined by using a computer program for statistical power, comparable cycling studies, and a preliminary pilot study.  The m i n i m u m  number of subjects necessary was estimated to be seven for phase I and ten for phase II (Schutz et al. 1987). The total group had similar characteristics to those  * Although subjects were in their prime condition, their availability for testing was limited by professional and personal commitments, as well as, the fact that testing coincided with the middle of the competitive season. Most athletes had races on weekends and two training sessions during the week. One athlete developed a running injury between the two phases of the study and thus did not participate in phase I. 28  reported for elite distance runners in Daniels et al. (1992). Subject characteristics for each phase are shown i n Tables 1 and 2.  Using a large and diverse group of distance runners as subjects w o u l d make the results of this investigation more generally applicable: however, i n this study the response of a specialized subgroup, elite distance runners, was examined to diminish the effects of confounding variables. The running speeds tested are submaximal and slightly below the current long distance race pace.  It is  expected that highly trained athletes w h o are competing at the elite level have optimized most aspects of their running mechanics and are capable of running comfortably at the running speeds being investigated. Another reason for testing this subgroup was that they are the ones w h o w i l l benefit the most if the hypotheses are proven correct.  Since individuals in this study were competitive distance runners, there existed the possibility that the prolonged maximal performance required i n competition could affect an individual's running economy and running mechanics (Cavanagh 1990); however, recent evidence suggests that a training run or 10 k m race does not produce a significant increase in the aerobic demand of running or the gait pattern i n subsequent short-term, submaximal runs (Morgan et al. 1990).  TESTING PROCEDURES T r e a d m i l l maximal oxygen consumption test. M a x i m a l oxygen consumption (VC>2max) was assessed  using a modified  continuous treadmill running protocol. The purpose of this test was three fold: a) to measure the maximal aerobic capacity of each subject while running; b) to assess at what percentage of maximal aerobic power subjects were utilizing  29  TABLE 1 Phase I: Subject Characteristics  Subject  Age  Mass (kg)  Height (cm)  V02max  (ml / m i n /kg)  1 2 3 4 5 6 7 8 9  26 27 32 32 19 34 24 20 28  73.9 76.5 78.0 68.0 71.2 69.9 70.3 75.0 62.6  185.4 185.9 175.0 175.3 184.2 170.2 175.3 183.1 170.2  73.4 62.4 71.9 60.4 61.9 68.4 66.7 68.2 56.5  Mean Std. Dev.  26.8 5.3  71.7 4.7  178.3 6.4  65.5 5.6  TABLE 2 Phase II: Subject Characteristics  Subject  Age  Mass (kg)  Height (cm)  V02max  ( m l / m i n /kg)  1 5 8 11 12  26 19 20 26 20  73.9 71.2 75.0 73.9 74.8  185.4 184.2 183.1 175.3 188.0  73.4 61.9 68.2 74.3 66.3  Mean Std. Dev.  22 3'  73.8 1.5  183.2 4.8  68.8 5.1  30  during the track testing; and c) to assess and compare the metabolic response of subjects to running on a treadmill versus a windless, flat, unbanked wooden oval track.  The purpose and procedure of the test were clearly explained to the subjects prior to the test, as were the test objectives and the criteria for terminating the test. Subjects were instructed to report to the laboratory in a three hour postprandial state and to refrain from strenuous physical activity on the day of the test. O n arrival to the laboratory, subjects had their height and weight taken. Body weight included that of clothing since it will contribute to the workload. Height was measured with shoes removed. Subjects who had never run on a Quinton treadmill were required to participate in a practice run. This was optional for subjects with previous treadmill experience.  A l l subjects were  required to stretch and warm-up according to personal preference.  The aim of  the practice run was to accustom the subject to running on a motorized treadmill. After allowing these subjects to warm-up and stretch, they ran on the treadmill for at least 15 minutes at 2.24 m / s at 0 % grade.  A t the start of the test, the subject was equipped with a belt E C G and pneumotach. The subject warmed-up for a period of 5 minutes on the treadmill at 2.24 m / s and 0 % grade. Treadmill speed was then increased to 3.13 m / s after 1 minute with 0.22 m / s increases every 1 minute. When the speeds of 4.47 m / s and 5.36 m / s were reached, the subject was required to run for 2 minutes instead of 1 minute before the speed was increased by 0.22 m / s . The test was terminated when the subject met at least two of the following criteria for attaining  V02max:  a) the point at which the subject voluntarily indicated fatigue (by grasping the  31  treadmill's handrails or becoming unable to maintain their position on the treadmill), b) a plateau i n V 0 2 , c) a respiratory exchange ratio > 1.10.  Expired gases were sampled w i t h either the C P X - D analyzers and recorded by the Medical Graphics computer system, or the AeroSport Teem 100. The peak V O 2 values obtained from eight subjects w h o were tested w i t h both systems were compared.  Paired t-tests of the V 0 2 m a x values obtained indicated no  significant differences between the two systems. Kearney (1995) and several other  V . Katch (1995) and J.T.  investigators have reported  similar  observations w h e n comparing the AeroSport Teem 100 to traditional large calorimeter systems  (Novitsky et al. 1995, Segal et al. 1994, Segal et al. 1995).  Heart rate was collected w i t h a portable Polar H R unit. A n additional group of five subjects ran for 5 minutes on the treadmill at 4.47 m / s to confirm that steady-state was being reached during V 0 2 m a x testing. The C P X - D / M e d i c a l Graphics system was utilized for these runs.  Experimental test. A l l trials of the experiment were conducted at the same time of the day (late evening) to minimize circadian rhythm effects. Testing was conducted i n a large flat wooden floored showroom, the ShowMart, at the P.N.E. i n Vancouver, B.C.. A 200 m track was marked w i t h traffic cones. Athletes were randomly assigned the order of testing on the day of the test. Subjects w h i c h had not participated i n previous related investigations were required to do a practice to ensure that the subjects were familiar w i t h the experimental procedure and minimize learning effects. Subjects were also asked to practice forming the different drafting configurations.  32  Prior to testing, the subject warmed-up and stretched according to personal preference. The subject was instructed on his running position and running pace. The subject was then equipped w i t h the belt E C G and pneumotach.  A  rollerblader carried the portable AeroSport Teem 100 i n a chest carrier behind the subject.  The subject reached the experimental speed i n the first lap and  continued running at the set pace for the next five laps. A t the end of the sixth lap, the subject stopped running at the finish/start point, was relieved of the test equipment, and was asked to rate his perceived exertion using the Borg scale. The subject was then required to recover passively for 15 minutes. D u r i n g this time, the subject was seated i n the recovery room and connected to a portable pulse oximeter and a portable respiratory/carbon dioxide analyzer to ensure that the subject's heart rate and respiratory rate returned to pretrial values prior to the start of the subsequent trial. This procedure also ensured the same recovery conditions for all subjects.  A l l testing and data collections were conducted at the same site w i t h the subject always running i n the same counter-clockwise direction. Room temperature and humidity were recorded on each test session. To ensure that the warm-up and test paces were reached and maintained throughout each trial, a pace cyclist/investigator equipped w i t h a CatEye M i t y 2 cycle computer rode closely behind the test group, and indicated verbally to the runners if they should adjust their pace or position. In addition, each lap was timed w i t h a stop watch by a spotter w h o verbally indicated if and by how much the time was off the set lap time for the given pace. Three highly skilled rollerbladers carried the portable indirect calorimeter during the experiment. They bladed approximately 1.5 m behind the subject at the 4.47 m / s pace and 2.5 m behind the subject at the 5.36 m / s pace.  33  Experimental conditions.  In phase I, nine subjects were tested i n three positions at 4.47 m / s .  The first  position, leading (L) was the control. Each subject performed the above protocol while running solo. The second position, drafting-1 (DI) was an experimental condition. In this position, the subject ran 1 m directly behind a shield runner. The third position, drafting-2 (D2), was the other experimental condition. In this position, the subject ran on the inside 1 m behind the left shoulder of the leading shield runner w i t h another  shield runner beside h i m on the outside and 1 m  behind the right shoulder of the leading shield runner forming a triangle (see Figure 8). These positions were maintained throughout each trial.  A l l three  positions were tested on the same day w i t h a m i n i m u m of 15 minutes recovery time between trials. In phase II, a subgroup of five subjects was tested i n two positions, L and D I , at 4.47 m / s and at 5.36 m / s .  Both these positions were  tested on the same day w i t h a m i n i m u m of 15 minutes recovery time between trials.  A t the end of experiment, subjects were questioned on the different  configurations.  Data collection apparatus.  Manufacturer recommendations regarding operation and calibration of all test equipment was accurately followed.  The AeroSport Teem 100 ( A n n A r b o r ,  Michigan, U.S.A.) was 25.4 by 25.4 by 8.9 cm and weighed approximately 3.3 kg, and had a fully integrated 12 V rechargeable battery.  This system measured  ventilation volume w i t h a flat-plate orifice pneumotach, oxygen w i t h a galvanic fuel cell, and carbon dioxide by the principle of non-dispersive infrared analysis. Ambient air was used to zero the carbon dioxide sensor output. Prior to the start of each test day the system was warmed up for 5 minutes, and autocalibrated at  34  35  the start of every trial to ensure accuracy. Continuous 20 second samples of VO2, VCO2, V E , and H R were recorded during each test. The values obtained for all twelve subjects indicated that they reached steady-state within the second minute of each trial. Steady-state values (minute 3 - second to last reading) were used for analysis. After each test, data was printed out and manually entered into a computer for further analysis.  Experimental design.  The independent variable i n phase I was Position (factor 1 w i t h 3 levels). The different levels of factor 1 were three different running positions, leading-L, drafting-1, and drafting-2. The independent variables i n phase II were Position (factor 1 w i t h 2 levels), and Speed (factor 2 with 2 levels). The two levels in factor 1 were running positions leading-L and drafting-1. The two levels i n factor 2 were the running speeds of 4.47 m / s and 5.36 m / s . The dependent variables for this study were VO2, VCO2, V E , H R , and RPE.  Statistical analysis.  The statistical analysis used to investigate the effects of drafting on VO2, V C 0 2 , and V E i n phase I was a one-way multivariate analysis of variance ( M A N O V A ) w i t h repeated measures followed by univariate analyses of variance w i t h repeated measures ( R M A N O V A ) for each dependent variable. The statistical analysis used to investigate the effect of drafting on H R and R P E were two onew a y repeated measures analysis of variance ( R M A N O V A ) .  The level of  significance was p< 0.05. The mean value of VO2, VCO2, V E , and H R were computed for each experimental condition. Preplanned orthogonal contrasts were used to compare means of VO2, V C 0 2 , V E , H R , and R P E . The following contrasts were made for VO2, VCO2, V E , and H R between drafting and leading  36  conditions ((Dl+D2)/2 vs. L ) , and between drafting conditions (DI vs. D2). The following contrasts were made for R P E between leading and drafting directly behind (L vs. D I ) and between leading and drafting i n the triangle configuration (L vs. D2). A paired t-test was used to compare leading and treadmill VO2 means at the test speeds (p<0.05). Due to the small sample size (n=5) in phase II, no statistical analyses were conducted on these results.  37  CHAPTER FOUR RESULTS Descriptive Statistics. Table 3 contains the means of the four physiological variables and rating of perceived exertion for the nine subjects i n the three running positions, as well as, the combined drafting effect, the average of both drafting positions. The percent reduction i n oxygen consumption was 5.2 % for both drafting positions. D u r i n g the leading trials, subjects were running o n average at 85.6 % of their maximal aerobic capacity. D u r i n g the drafting trials, subjects were running o n average at 81.1 % of their m a x i m a l aerobic capacity.  C a r b o n dioxide production was  reduced approximately the same for both drafting positions, 12.3 % i n position D I and 10.4 % i n position D2. M i n u t e ventilation was only reduced 1.7 % i n position D I and 1.0 % i n position D2. Heart rate increased slightly i n position D I , 1.9 %, and remained the same i n position D2. The rating of perceived exertion dropped by one point i n position D2 (see Figure 9).  Table 4 contains the means and standard deviations of the four physiological variables and rating of perceived exertion for the subgroup of five subjects i n the two r u n n i n g positions at the two running speeds. The percent reduction i n oxygen consumption for this subgroup was 7.3 % at 4.47 m / s and 8.6 % at 5.36 m / s . D u r i n g the 4.47 m / s trials, subjects on average ran at 83.5 % of their aerobic capacity while leading, and at 77.4 % while drafting i n position D I . D u r i n g the 5.36 m / s trials, subjects on average ran at 93.7 % of their aerobic capacity while leading, and at 85.6 % while drafting i n position D I . Carbon dioxide production  38  TABLE 3 Phase I : Physiological responses to different running positions.  Position  V O 2  V C O 2  (1/min)  VE (1/min)  HR (beats/min)  RPE  (1/min) Leading  4.02 ± 0.18  3.74 ± 0.23  82.6 ± 4.3  150 ± 6  12.4 ± 0 . 4  Drafting  3.81 ± 0.13  3.32 ± 0.13  83.4 ± 2 . 8  151 ± 4  11.4 ± 0 . 6 *  DI  3.82 ± 0.12  3.28 + 0.16  83.1 ± 2 . 5  152 ± 4  11.8 ± 0 . 6  D2  3.80 ± 0.15  3.35 ± 0 . 1 2  83.6 ± 3 . 4  150 ± 5  11.1 ± 0 . 6 *  Values are mean ± sem. (n=9) * Significantly different from leading.  39  14  F I G U R E 9:  r  Percent reduction i n oxygen c o n s u m p t i o n , carbon d i o x i d e production, minute ventilation, heart rate, and R P E as a result of drafting in positions D I and D2.  40  was reduced 8.2 % at 4.47 m / s and 6.3 % at 5.36 m / s . M i n u t e ventilation was reduced by 5.0 % at 4.47 m / s but remained the same at 5.36 m / s . Heart rate was reduced slightly at 4.47 m / s , 2.3 %, and increased by 8.4 % at 5.36 m / s (see Figure 10).  Comparisons among means.  The steady state values for oxygen consumption during the treadmill maximal oxygen consumption test w h e n the subjects were running at 4.47 m / s were compared using paired t-tests to track test results for the leading trials. Oxygen consumption was found to be significantly lower by 0.78 ± 0.12 1/min, 19.1 %, on the treadmill at 4.47 m / s (n=12, p < 0.05).  Multivariate analysis of variance (Table 5) revealed a significant VO2-VCO2-VE difference i n the position i n w h i c h subjects ran, F m (Pillais) = 3.16, p < 0.016. Follow-up univariate A N O V A s indicated that this significant metabolic effect was due to differences i n oxygen consumption and carbon dioxide production between the trials (where leading trials had higher values than drafting trials for both variables).  Preplanned orthogonal contrasts indicated that there were  significant reductions i n oxygen consumption and carbon dioxide production during drafting trials i n general (p < 0.048, p < 0.004); however, there were no significant differences between the two drafting positions. Analysis of variance revealed that there was not a significant position main effect on heart rate, F (Huynh-Feldt) = 0.18, p < 0.78. Preplanned orthogonal contrasts indicated that there were no significant reductions heart rate during drafting trials i n general (p < 0.72), nor between the two drafting positions (p < 0.61).  41  TABLE 4 Phase II: Physiological responses to different running positions while running at 4.47 and 5.36 m / s .  Position  VO2  (1/min)  VCO2 (1/min)  VE (1/min)  HR (beats/min)  RPE  Speed = 4.47 m / s Leading  4.24 + 0.16  3.67 ± 0 . 1 6  89.2 ± 8 . 0  149 ± 5  11.3 + 1.0  DI  3.93 ± 0 . 1 9  3.37 ± 0 . 1 9  84.7 ± 5 . 8  145 ± 6  11.4 ± 0 . 5  Speed = 5.36 m / s Leading  4.76 ± 0.20  4.44 ± 0.28  110.2 ± 6 . 4  154 ± 10  13.8 ± 0 . 6  DI  4.35 ± 0.20  4.16 ±0.26  109.8 ± 4 . 0  167 ± 5  13.3 ± 0 . 7  Values are mean ± sem. (n=5)  42  F I G U R E 10:  Percent reduction i n oxygen c o n s u m p t i o n , carbon d i o x i d e production, minute ventilation and RPE as a result of drafting i n position D I while running at 4.47 and 5.36 m / s .  43  TABLE 5 M A N O V A Summary  Effect  Position  Multivariate F (Pillais) (p)  3.16 (0.016)  Univariate (dependent var. s sig at < 0.05) VC>2  VCO2  VE  Sig. (0.048)  Sig. (0.004)  n.s.  44  Analysis of variance revealed that there was a significant position main effect on the rating of perceived exertion, F (Huynh-Feldt) = 5.75, p < 0.016. Preplanned orthogonal contrasts indicated that this position effect was due to a significant reduction in perceived exertion for the drafting position D2 w h e n compared to leading (p < 0.011). N o significant reduction was found between leading and drafting i n position D I (p < 0.09).  Survey Data. Runners' opinions on drafting and the positions tested are shown in Table. 6.  45  TABLE 6 Survey Results Numbers indicate the number of subjects who responded out of a total of twelve subjects who participated in the study. Most energy consuming position  Leading: 0  Drafting : 12  Most energy efficient position  Leading: 0  DI: 0  D2: 11  Felt constricted while drafting  Yes: 5  N o : 7.  Least constricting drafting position  Dl:2  D2:4  Feel comfortable leading  Yes: 9  No: 3  Feel comfortable drafting  Yes: 12  No:0  Most comfortable position  Leading: 1  DI: 0  D2: 11  Second most comfortable position  Leading: 1  D I : 11  D2: 0  Third most comfortable position  Leading: 10  DI: 1  D2: 1  Most applicable position for competition  Leading: 0  DI: 0  D2: 12  Second most applicable position  Leading: 4  DI: 8  D2: 0  Third most applicable position  Leading: 8  Dl:4  D2: 0  46  Results of Hypotheses.  V O 2 Leading Track > V O 2 Leading Treadmill  Accept  V O 2 Leading * V O 2 Drafting - D I * V O 2 Drafting - D 2  Accept  V O 2 Leading > V O 2 Drafting (DI + D2)  Accept  V O 2 Drafting - D I > V O 2 Drafting - D 2  Reject  V C O 2 Leading  Accept  * V C O 2 Drafting - D I * V C O 2 Drafting - D 2  V C O 2 Leading > V C O 2 Drafting (DI + D2)  Accept  V C O 2 Drafting - D I > V C O 2 Drafting - D 2  Reject  V E Leading * V E Drafting - D I * V E Drafting - D 2  Reject  V E Leading > V E Drafting (DI + D2)  Reject  V E Drafting - D I > V E Drafting - D 2  Reject  H R Leading * H R Drafting - D I * H R Drafting - D 2  Reject  H R Leading > H R Drafting (DI + D2)  Reject  H R Drafting - D I > H R Drafting - D 2  Reject  RPE Leading * R P E Drafting - D I * R P E Drafting - D 2  Accept  RPE Leading > R P E Drafting - D I  Reject  RPE Leading > R P E Drafting - D 2  Accept  47  C H A P T E R FIVE DISCUSSION  A i r Resistance. A i r resistance results from the normal forces exerted by air molecules hitting the body and from the air friction caused by air molecules sliding along the bodies surface. During treadmill running, the ground moves backwards relative to the runner.  A i r molecules move only around the m o v i n g body segments.  While  during track running, both the ground and the air molecules move backwards relative to the runner.  There is general agreement i n the literature that at low to  moderate running speeds, 2.27 - 4.33 m / s , the aerobic requirements of track running and treadmill running are equivalent (Davies 1980, M c M i k e n et al. 1976, Morgan et al. 1992, M a k s u d et al. 1971). A t more strenuous running speeds, 4.47 - 6.0 m / s , several investigators have found significant differences between the aerobic demands of the two running environments. M a k s u d et al. (1971) found that oxygen consumption on the track increased approximately 8 %, 0.3 1/min, while running at 4.47 m / s , and 10 %, 0.4 1/min, while running at 5.36 m / s . Daniels et al. (1985) found that at this same speed range oxygen consumption was increased by 7.1 % during level ground running in calm air when compared to level treadmill running. Similarly w h e n P u g h (1970) compared track and treadmill running at 6 m / s on two athletes, he found that oxygen consumption on the track increased 8.4 %, 0.39 1/min. From the above work, it appears that the aerobic demands of running on the track in calm air w o u l d be 8 -10 % higher than that of running on a treadmill.  A l l these studies were conducted on different types of tracks. Daniels et al. and Pugh conducted their tests on cinder or all weather tracks. Possible sources of  48  error on the outdoor tracks could arise from the presence of slight w i n d s undetectable w i t h the w i n d gages of the time.  One of the advantages of  conducting tests i n indoor tracks is the added control over the environmental conditions.  M a k s u d et al. (1971) conducted their track tests on a 128 m banked  indoor track, and i n the present study a 200 m wooden, flat, unbanked indoor track was used.  A n o t h e r factor w h i c h c o u l d have influenced the results of these early investigations on the effects of air resistance is that expired air was collected from the runner by the Douglas bag method. M a k s u d et al. (1971) had the runner carry a Douglas bag on his back while running. P u g h (1970) used a vehicle to carry the collection equipment and drove next to the runner w i t h a wind-screen. Needless to say, the face mask and collection apparatus may have been slightly cumbersome for the runners and could have affected them both psychologically and physiologically resulting i n smaller increases i n running economy d u r i n g treadmill tests (Montpetit et al. 1981). In the present study, the mouth-piece and pneumotach hose w o r n by subjects was much less obtrusive and weighed less than 100 g.  Oxygen consumption was increased 0.78 1/min or 19.1 % at 4.47 m / s w h e n running on a wooden, flat, unbanked indoor track.  The difference between  treadmill r u n n i n g and track r u n n i n g was approximately double to that of previous studies.  Subjects were running at 86.0 % of their maximal aerobic  capacity on the track and at 69.6 % of their maximal aerobic capacity on the treadmill. The differences i n equipment and track environment from previous studies are likely the main reasons for the different findings. The consistency of the oxygen cost of treadmill running results and their agreement w i t h previous  49  published work (Conley et al. 1980, Costill et al. 1973, Davies 1980, M a k s u d et al. 1971, Pollock 1977) provide evidence of the accuracy of the oxygen consumption measurements.  Intuitively, air resistance is the main difference between our two sites. It could be that the methodological procedures used to measure respiratory gases i n previous studies masked the extent to w h i c h air resistance affected running economy. Another reason for the observed decrease i n running economy could have arisen if the athletes biomechanics differed on the two sites. The surface of the wooden running track was smoother than that of the treadmill's rubberized running platform. Biomechanical changes may have been caused by differences in surface and ground compliance, as w e l l as, increased slippage. O n springy tracks the time spent rebounding from the surface is increased, so that a runner is slowed d o w n and must work harder to maintain a set pace ( M c M a h o n et al. 1978). However, the degree to w h i c h this actually could have affected running economy is likely to be quite small in comparison to the 19.1 % decrease. Stride length, the most important biomechanical variable at the test speeds, w h e n adjusted has been reported to affect oxygen consumption by 3.8-2.1 % (Heinert et al. 1980). Moreover, i n a study comparing several track surfaces, only a 2.91 0.26 % difference i n performance time was reported (McMahon et al. 1978). The increase in aerobic cost found in this study is probably a more accurate reflection of the extent to w h i c h both air resistance and motorized treadmill running surfaces affect running economy.  Shielding runners from air resistance.  A l t h o u g h running i n the aerodynamic shadow of another runner is w i d e l y recommended in popular running magazines and the sports science literature,  50  there are athletes and scientists w h o feel that air resistance only costs a small percentage of their total energy and that the effects on running economy are negligible until y o u reach the higher sprint velocities (Schmidt-Nielsen 1972, Strnad 1985). From the huge differences observed between treadmill and track r u n n i n g , it is obvious that air resistance costs l o n g distance runners a considerable percentage of their total energy. A n y tactic w h i c h can reduce this cost w o u l d be very advantageous.  Oxygen Consumption. In the present investigation, the employment of drafting positions during indoor track runs at 4.47 m / s resulted i n an average drop i n oxygen consumption of 0.21 1/min. This is a 5.2 % improvement i n running economy. Pugh (1971) observed a 0.25 1/min reduction in oxygen consumption when his subject was running on a treadmill at 4.5 m / s against a 6.0 m / s head w i n d . In the pilot study conducted by Corvalan-Grossling et al. (1994), a 0.22 1/min reduction i n one minute postexercise oxygen consumption was observed for subjects running at 4.47 m / s i n an oval corridor. Both Pugh's observations for a single subject, as w e l l as, the pilot data show a remarkable degree of agreement w i t h the present results. It appears that drafting reduces oxygen consumption by 0.19- 0.25 1/min w h e n running at 4.47 m / s in calm air.  The largest reduction i n oxygen consumption produced b y drafting was 0.72 1/min for subject no. 8. This reduction is the same as the one first observed in a preliminary case study by Corvalan-Grossling (1994) on another runner who d i d not participate i n this investigation. There were two subjects out of the total twelve for w h o m drafting d i d not result in a reduction i n oxygen consumption. For one, subject no. 2, oxygen consumption remained relatively constant  51  throughout the experiment; while, for the other, subject no. 9, drafting i n both positions increased his oxygen consumption b y approximately 0.32 1/min. Drafting was found to be an effective tactic for reducing oxygen consumption for the majority of subjects.  The main premises of this study have been that a significant amount of energy is utilized by runners to overcome air resistance at the long distance running paces, and that air resistance and the net energy expenditure of a runner can be reduced by drafting behind another runner. There are several secondary mechanisms by which drafting could have improved running economy. One means could have been the synchronization of gait patterns between the shield and the drafting runners. The drafting runner, especially when i n position D I , could also have adjusted his biomechanics to avoid being kicked by or b u m p i n g the shield runner. Biomechanical modifications, subconsciously, could have resulted from the reduction i n aerodynamic drag forces. Synchronization, as w e l l as, these other sources of biomechanical modifications could have improved some of the subjects' biomechanical efficiency. However, as mentioned earlier, relatively small changes i n oxygen c o n s u m p t i o n have been found to considerable  changes  i n stride length a n d  frequency,  accompany  i n d i c a t i n g that  biomechanical changes could only have accounted for a portion of the observed effect (Brandon et al. 1992, Cavanagh et al. 1982).  One possible means of d i s t i n g u i s h i n g h o w m u c h aerodynamic drag and biomechanics contributed to the effects of drafting could be to reproduce the study on a different type of athlete such as cyclists. The test pace of 4.47 m / s w o u l d be easily maintained by cyclists. Consequently, there w o u l d be very little variation in their pedal frequency or kinematics. Changes i n the drafting trials  52  w o u l d theoretically be solely due to reductions i n aerodynamic drag. It w o u l d be assumed that both groups, cyclists and distance runners, expend the same amount of energy to overcome air resistance and that if there is a psychological factor involved, it w o u l d be the same for both groups.  Thus, if the cyclists  oxygen consumption was decreased by the same amount as the long distance runners i n this study, it w o u l d indicate that the effect of drafting on oxygen consumption was due to the reduction i n air resistance and factors other than biomechanical modifications.  Another secondary mechanism by w h i c h drafting may have influenced running economy could involve psychological factors. For example, mental concentration levels may have shifted during the test trials. L o w levels of concentration during running tests have been associated w i t h higher rates of oxygen consumption (Morgan et al. 1977). Subject's mood state may also have differed during the test trials. Positive mood states and l o w tension levels are strongly associated w i t h lower rates of oxygen consumption i n elite distance runners.  Some subjects,  w h e n questioned at the end of the experimental session, stated that drafting permitted them to tune-out for a few moments d u r i n g the test intervals. Subjects' rating of perceived exertion was reduced by one full unit d u r i n g drafting-2 trials. Evidence has been found by M o r g a n (1992) that relaxationbased cognitive activity reduces oxygen consumption d u r i n g submaximal exercise. It is possible that drafting permits athletes to reduce their arousal and stress  levels. Taking as their o w n a competitor's pace may allow distance  runners to relax during portions of a race.  53  Carbon Dioxide Production. In the absence of portable carbon dioxide analyzers, carbon dioxide was seldom evaluated i n air resistance and drafting studies. Oxygen consumption, w h i c h was and still is of primary interest due to its close relationship to running performance, was always measured and a respiratory ratio of RER=1 was usually assumed. Oxygen consumption and carbon dioxide production are very closely associated especially at submaximal levels of exercise where there is m i n i m a l production of lactic acid and the bicarbonate buffer system is less taxed. It was of great interest to observe how one of the waste products of muscle metabolism reacted to an energy saving strategy and if it m i r r o r e d that of oxygen consumption. The employment of drafting positions during indoor track runs at 4.47 m / s resulted i n an average drop in carbon dioxide production of 0.42 1/min. This 11.1 % reduction is approximately double the reduction observed for oxygen consumption. In the pilot study, a similar reduction of 0.31 1/min was observed i n the one minute post-exercise carbon dioxide production rate during test trials i n position D I . A similar but less pronounced difference between the reductions i n carbon dioxide production and oxygen consumption.  In the present investigation, the largest reduction i n carbon dioxide production due to drafting of 1.40 1/min was for subject no. 3. The reduction i n carbon dioxide production for this subject was m u c h larger than for most; however, similar results were observed for this subject i n pilot trial, and the same reduction was observed for both drafting positions (DI and D2). T w o subjects, no. 6 and no. 11, had very small reductions i n carbon dioxide production, just 0.08 1/min. subjects.  But, drafting reduced carbon dioxide production i n all twelve  From the significant reduction i n oxygen consumption and the even  larger reduction in carbon dioxide production, drafting appears to improve  54  running economy and reduce the production of metabolic bi-products i n highly trained distance runners.  M i n u t e Ventilation. Reductions i n oxygen consumption sometimes occur as a result of decreases i n minute ventilation resulting from reduced breathing frequency and an increased tidal volume.  This was not the case i n the present investigation. M i n u t e  ventilation was not affected by the employment of drafting positions at 4.47 m / s and remained at approximately 83 1/min.  The relationship between minute  ventilation and oxygen consumption can be affected b y the c o u p l i n g of respiratory and locomotor rhythms. Loring (1990) found that individuals w h o breathed i n rhythm w i t h stepping frequency while w a l k i n g on a treadmill could have their metabolic rate increase substantially by increasing the percent grade, while walking at the same constant pace, without affecting breathing frequency. M a k s u d et al. (1971) similarly found that oxygen consumption was significantly different between the two running environments, treadmill and track, at the same test speeds of 4.47 m / s and 5.36 m / s , while minute ventilations, as well as, heart rates were not significantly different irrespective of the changes i n air resistance.  The c o u p l i n g of respiratory and locomotor rhythms, also referred to as respiratory entrainment and mammalian locomotor respiratory coupling, has been long suspected of occurring spontaneously during rhythmic exercise. In sports such as cycling, r o w i n g , and s w i m m i n g , this c o u p l i n g is developed intentionally in order to improve performance (Bramble 1983, Garlando 1985, Mahler 1991). In running, the coupling of respiratory and locomotor rhythms is most likely a spontaneous unconscious event. Bramble (1983) reported that there  55  is a clear tendency i n highly trained runners to synchronize respiration and body motion during sustained running and that in the majority this phase locking can occur as quickly as the first five strides of a run.  It is interesting that although carbon dioxide production, in the present study, was significantly reduced during the drafting trials, minute ventilation remained the same. A t rest, even small elevations i n carbon dioxide partial pressure i n arterial plasma w i l l stimulate a large increase i n minute ventilation. D u r i n g exercise, however, a combination of simultaneous input from several chemical and neural stimuli control minute ventilation. In this case, neural stimuli from the motor cortex and peripheral mechanoreceptors seem to have had a predominant role i n regulating respiration and possibly synchronizing it to limb movement. This change i n the importance between respiratory regulators w o u l d also explain the difference i n results between M a k s u d et al. (1971), the present study, and the pilot study.  In the pilot study, respiratory gas samples were  collected using the Douglas bag method one minute post-exercise while subjects were completely stationary. In this situation, it w o u l d be quite reasonable to infer that the chemical stimuli, carbon dioxide partial pressure and blood p H , w o u l d have been the predominant respiratory regulators.  Heart Rate. The relationship between heart rate and oxygen consumption appears to be quite simple and predictable.  A s the energy demands of exercise increase w i t h  increasing exercise intensity, the heart is required to p u m p blood faster and a greater amount of oxygen is consumed by the body. It is a w e l l documented relationship w h i c h tends to be linear throughout a large segment of the aerobic work range (Bunc et al. 1988, Haskel 1993, M c A r d l e et al. 1991, McGinnes 1995,  56  Pate et al. 1989, Pate et al. 1992, Schoeller 1990). Currently, equations are being developed and modified to equate heart rate to oxygen consumption so that only heart rate measurements are required for determining the energy cost of a training session or a specific activity (Dishman 1994, Haskel 1993). It is also well k n o w n that the relationship between heart rate and oxygen consumption can be influenced by other variables, including environmental conditions, food intake, body posture, the muscle groups utilized during an activity, continuous versus discontinuous exercise, isometric versus rhythmic exercises, as w e l l as, athletes psychological status ( Haskel 1993, M c A r d l e et al 1991, Schoeller 1990). In the present  investigation, environmental  conditions  remained  constant.  Theoretically , limb movement was the same d u r i n g all test trials at the set running paces. The only factor w h i c h could not be controlled was the subjects psychological status. The employment of drafting positions while running at 4.47 m / s d i d not affect heart rate. Similar heart rate results were observed i n the pilot study for one minute post-exercise and exercise measurements.  M a k s u d et  al (1971) also found the same effect during treadmill versus track experiments. Both limb movement and psychological stress could have been involved i n the heart rate responses.  H o w e v e r , considering that oxygen consumption was  reduced during the drafting trials while heart rate remained the same and that the correlation between psychological tension and oxygen consumption is as high as r=0.81 (Crews 1992), it w o u l d be reasonable to infer that the fact that heart rate d i d not go d o w n was not due to increased stress but due to locomotor and cardiac r h y t h m c o u p l i n g .  N i i z e k i et al (1993) has reported  such  s y n c h r o n i z a t i o n d u r i n g t r e a d m i l l exercise between heart rate and l i m b movements i n untrained i n d i v i d u a l s . Athletes, especially at the elite level, w o u l d tend to have a larger degree of entrainment and it is therefore possible that a very strong interrelationship between cardiac, locomotor, and respiratory  57  rhythms may be present. Nevertheless, it is also possible that the psychological stress of having to draft behind a competitor may have limited the reduction i n oxygen consumption observed.  This c o u l d explain w h y carbon d i o x i d e  production was reduced twice as much as oxygen consumption and w h y heart rate was not significantly reduced.  Drafting Positions and Subject's Perceptions. In this investigation, subjects perceived a difference between the two drafting positions. The rating for perceived exertion i n position D2 was one full unit lower than that for leading; while, the rating for position D I was essentially the same as that for leading. A l l subjects stated that position D2 felt the most efficient and applicable as a racing tactic. Eleven of the twelve felt that position D2 was the most comfortable of the three positions, and four out of six runners stated that it was the least constricting drafting position.  However, contrary to what subjects perceived, both drafting positions, D I and D2, resulted i n the same physiological responses. O x y g e n consumption and carbon dioxide production were reduced by the same proportion i n both positions when compared to leading trials; while, minute ventilation and heart rate remained relatively constant. There are two possible reasons as to w h y nearly identical physiological responses were found. One explanation is that both drafting positions provided runners w i t h the same degree of shielding from aerodynamic drag forces and therefore  resulted i n similar p h y s i o l o g i c a l  responses w h i c h were independent of psychological or perceived differences between the two positions. This explanation does not seem plausible if one considers 1) the strong association w h i c h exists between perceived exertion and  58  oxygen consumption (McGinnes et al. 1995, Skinner et al. 1973, Steed et al. 1994, Williams et al. 1990), and 2) that although position D2 has never been studied, evidence provided by Pugh's pressure measurements (1970) and the results from work conducted on cyclists riding i n position D I , as well as, a position behind to the side, suggests that position D I w o u l d protect athletes from aerodynamic drag forces to a greater extent than position D2 (Kyle 1979, M c C o l e et al. 1990). The alternate explanation is that these two drafting positions d i d not provide runners w i t h the same degree of shielding from aerodynamic drag forces, but that the combination of several different factors, physical, psychological and possibly biomechanical, produced the same physiological effects for both positions.  R u n n i n g Speed and Drafting. Through the cycling studies conducted by Kyle (1979) and M c C o l e et al. (1990), it has been demonstrated that the reduction i n energy expenditure w h i c h results from drafting directly behind another rider increases at faster riding velocities. In the present investigation, a similar trend was observed.  The reduction i n  oxygen consumption increased 0.10 1/min at the faster pace (see Table 6). Subjects ran at 83.5 % of their maximal aerobic capacity at 4.47 m / s and 93.7 % of their maximal aerobic capacity at 5.36 m / s when leading. W h e n subjects drafted in position D I , they ran at 77.4 % of their total aerobic capacity at 4.47 m / s and at 85.6 % of their total aerobic capacity at 5.36 m / s .  Therefore, drafting directly  behind another runner i n position D I at 5.36 m / s was approximately equivalent to leading at 4.47 m / s i n terms of aerobic energy expenditure.  In this subgroup of five runners, the reduction i n carbon dioxide production due to drafting in position D I were essentially the same. A t the 4.47 m / s pace, both  59  oxygen consumption and carbon dioxide production were reduced by equal amounts, while, average minute ventilation and heart rate remained the same. This strongly supports the theory that respiratory, cardiac and locomotor coupling occurred. A t the 5.36 m / s pace, the reduction in oxygen consumption exceeded that of carbon dioxide production.  This was most likely due to  increasing levels of lactic acid. M i n u t e ventilation again remained constant, while, heart rate fluctuated slightly. The rating of perceived exertion d i d not change i n either of the two paces confirming the observations made for position D I at 4.47 m / s for the nine runners.  60  CONCLUSIONS AND RECOMMENDATIONS Each athlete w i l l react differently to drafting tactics. In ten out of twelve of the runners tested, drafting as close as possible, approximately 1 m , behind runners produced significant reductions i n oxygen consumption i n the range of 5.2 %, and all twelve experienced significant reductions in carbon dioxide production i n the range of 11.1 %. A l l subjects who participated i n this study felt that they consumed more energy while leading than while drafting. Considering that a difference as small as 1 % can exist between the Gold-Medalist and nonmedalists at W o r l d C h a m p i o n s h i p competitions, the degree to w h i c h drafting can p h y s i o l o g i c a l l y benefit  distance  runners has  definite  i m p l i c a t i o n s on  performance times. Moreover, if one considers the pacing behavior of distance runners i n competition w h i c h is to accelerate during the terminal stages, drafting w i l l enable runners to conserve energy for this critical stage while still running a fast race (Foster et al. 1994). In calm air the aerobic energy cost of overcoming air resistance was found to be 19.3 %, drafting reduced the aerobic energy cost of overcoming this force by 25 %.  In outdoor races where runners can find  themselves running against strong head winds, drafting w i l l likely reduce this even more.  O n the basis of the experimental results, running directly behind another runner (position D I ) and running in a triangle on the inside of a lead runner's shoulder and w i t h another runner next to y o u (position D2) produce the same reductions in energy expenditure.  H o w e v e r , position D2 received a lower rating for  perceived exertion, was found to be the most comfortable, and strategically applicable to races by the majority of runners. Position D2 is more strategically sound than position D I because it reduces a runners risk of getting boxed in. It is  61  important to distinguish position D2 from just r u n n i n g on a lead runner's shoulder. The latter position w o u l d not be as advantageous as drafting directly behind a runner i n position D I . The next best racing position was determined to be drafting directly behind another runner. Especially considering that drafting in this position at 5.36 m / s required approximately the same amount of energy as leading at 4.47 m / s .  A l l this being said there are certain circumstances where drafting w o u l d not be recommended. For instance, it w o u l d be detrimental for a runner to draft behind a competitor who has an uneven pace or an unpredictable stride. This situation w o u l d likely force the drafting runner to become less biomechanically efficient and the uneven pace may affect h i m psychologically. A n y advantage w h i c h could have been gained by being protected from aerodynamic drag forces w o u l d probably be lost. This is, however, a very good strategy for runners to use to prevent or deter other competitors from drafting behind them (Higdon 1978). 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Steed J., Gaesser G . A . , Weltman A . (1994). Rating of perceived exertion and blood lactate concentration during submaximal running. M e d . Sci. Sports Exerc, 26(6):797-803. Strnad J. (1985). Physics of long-distance running. A m . J. Physics, 53:371-373.  68  Tipler P . A . (1990). Physics, for Scientists and Engineers. Third Edition, v o l . 1. Worth Publishers, N . Y . , pp. 346-360. Williams K.R. (1984). The relationship between mechanical and physiological energy estimates. M e d . Sci. Sports Exerc, 17(3):317-325. Williams T.J., Krahenbuhl G.S., M o r g a n D . W . (1990). The relationship between the profile of m o o d states and r u n n i n g economy. M e d . Sci. Sports E x e r c , 22(S2):S92.  69  APPENDIX 1 DEFINITION OF T E R M S Aerodynamics  The systematic study of forces exerted by air or other gases (Halliday et al. 1988).  A i r Resistance  The pressure exerted on solid objects by still air (Pugh 1971).  Beneficial  Producing the following benefits: energy savings, least discomfort or constriction of movement, and applicable as a race strategy.  Entrainment  The interaction between two periodic events i n w h i c h one oscillator captures the frequency of another, resulting i n phase locking of the two rhythms at an identical or at an integer ratio of frequencies.  Efficiency  The relationship between w o r k done and energy expended.  Drafting  Following closely behind in the aerodynamic shadow of another athlete.  Drag  Term used i n aerodynamics w h i c h refers to the force exerted by air on a solid moving object (Pugh 1971).  Laminar Flow  F l u i d particles m o v i n g in smooth paths w i t h one layer gliding smoothly over an adjacent layer (Olsen et al. 1987).  M a x i m a l Aerobic Capacity (VC>2max)  The point during progressive exercise at w h i c h oxygen consumption ceases to rise and reaches a plateau or begins to fall even though the w o r k rate continues to increase (MacDugal et al. 1991).  Road Race Environment  Running on a flat, straight road.  Running Economy  The steady-state o x y g e n c o n s u m p t i o n for standardized running speed (Morgan et al. 1990).  70  a  Steady State Exercise  The intensity of exercise that can be performed for a p r o l o n g e d p e r i o d of time w i t h o u t appreciable elevations in V O 2 , H R , V E , or R E R .  Turbulent Flow  F l u i d particles m o v i n g w i t h an irregular t u m b l i n g motion (Olsen et al. 1989).  W i n d Resistance  The pressure exerted on solid objects by w i n d of a given velocity (Pugh 1971).  71  APPENDIX 2 CASE STUDY  The physiological effects of drafting on an elite level distance runner. V . Corvalan-Grossling, J. Taunton, D. Clement, D. McKenzie, K. Coutts School of H u m a n Kinetics , The University of British Columbia  ABSTRACT The metabolic responses of an elite level distance runner while running i n two positions, leading and drafting-1, at 4.47 m/s were investigated. Testing was conducted outdoors on a level, gravel road.  Oxygen consumption, minute  ventilation, and heart rate were measured every 15 seconds during the six minute run and for  the first two minutes of the recovery phase using a  Cosmed K2 portable telemetry system. Following both trials, the runner was asked to rate his perceived exertion (RPE) using the Borg scale.  Running  directly b e h i n d another runner substantially reduced this subject's  oxygen  consumption (2.48 ± 0.04 1/min leading versus 1.76 ± 0.08 drafting), and minute ventilation (110.0 ± 2.0 1/min leading versus 89.4 ± 14.6 drafting).  Heart rate  was only slightly reduced (169 ± 11 beats/min leading versus 161 ± 10 beats/min drafting) while R P E was the same for reductions  in  oxygen  consumption  and  minute  evident during the first two minutes of recovery.  72  both trials (RPE = 11). The ventilation were  also  OBJECTIVE The purpose of this case study was: 1) to examine the metabolic effects of running directly behind another runner, 2) to obtain an estimate of the magnitude and short-term duration of the effects of drafting on selected variables, and 3) to evaluate the testing protocol and testing apparatus.  METHODS The Subject A highly trained and experienced male runner volunteered to participate i n this investigation. This athlete was a senior member of a university track team. By self-report, he trained i n excess of 40 k m / w e e k , competed i n distance events ranging from 5 k m to 10 k m , had been competitive for more than two years at the senior level, had completed a mile run i n a time of 5 minutes or less several times within the last two months of his participation, and was apparently healthy w i t h no musculoskeletal complaints or documented history of cardiorespiratory disease. The subject was fully informed of the risks and potential discomfort associated w i t h the testing procedures before giving his signed informed consent as required by the Behavioral Sciences Screening Committee for Research Involving H u m a n Subjects at the University of British Columbia. The subject had the following characteristics: age, 27, height, 162.0 cm, weight, 59.0 kg.  Testing Procedures The test site was a flat, straight 3 k m gravel road. Both trials were conducted i n the late evening to minimize w i n d , temperature, and circadian rhythm effects. Both trials were conducted on the same section of the course w i t h the subject r u n n i n g i n the same direction. Prior to the start of the trials, ambient air temperature, barometric pressure, w i n d speed and direction were obtained from  73  Environment Canada weather station next to the test site. Testing was not conducted i n the presence of a w i n d  (wind speed > 2.7 m / s ) or precipitation.  The subject was given a practice session at the test site to enable h i m to become accustom to the testing apparatus. After allowing the subject to warm-up and stretch according to his personal preference, a practice r u n at 4.47 m / s was performed. The subject was then tested leading. T w o days after the first session the subject was retested drafting directly behind another runner of larger physical b u i l d .  The testing sessions began after the warm-up and practice  session. The subject was equipped w i t h the portable Cosmed K 2 telemetry unit as shown i n Figure A l . The subject was then taken to the start and instructed when to begin running. W i t h the aid of a pace cyclist, the subject reached the experimental speed of 4.47 m / s i n the first 0.25 mile and continued running at this pace for 1 mile, running a total distance of 1.25 miles. A t the end of the trial, the subject was instructed to rest passively for 6 minutes. The subject was then relieved of the portable Cosmed K 2 unit. The subject then rated his perceived exertion using the Borg scale.  The pace cyclist equipped w i t h a CatEye M i t y 2  cycle computer rode closely behind the runner (s), recording time, distance, and average speed. To ensure that the subject maintained the 4.47 m / s pace and drafting configuration throughout the test, the pace cyclist continually verbally indicated to the subject any necessary adjustments and the travelling speed.  Test Apparatus The portable Cosmed K 2 telemetry unit (Rome, Italy) consisted of a transmitter, a battery, a face-mask/turbine flow meter assembly and a belt E C G monitor. The Cosmed K 2 portable telemetry system measured oxygen consumption, minute ventilation, and heart rate every 15 seconds during the six minute trial and for the first two minutes of the recovery phase.  74  FIGURE A l :  D i a g r a m of C o s m e d K 2 telemetry unit used to measure oxygen consumption, minute ventilation, and heart rate.  75  RESULTS & DISCUSSION R u n n i n g directly behind another runner substantially reduced this subject's oxygen consumption (2.48 ± 0.04 1/min leading versus 1.76 ± 0.08 drafting), and minute ventilation (110.0 ± 2.0 1/min leading versus 89.4 ± 14.6 drafting). Heart rate was only slightly reduced (169 ± 11 b e a t s / m i n leading versus 161 ± 10 b e a t s / m i n drafting) while R P E was the same for both trials (RPE = 11). The reductions in oxygen consumption and minute ventilation carried over for at least the first two minutes of recovery (see Figures A 2 , A 3 , and A4).  There are several factors which may have affected the results observed. External environmental factors included light winds (< 2.7 m / s ) , humidity, the gravel surface, and decreasing daylight. The decreasing daylight and poor visibility due to the face mask could have increased the anxiety level and thus affected the subject's heart rate during one, or both of the trials. The gravel surface may have affected the subject's biomechanics thus affecting the physiological variables. This subject by self-report preferred leading during races and d i d not normally use drafting as a training or racing strategy. H i s unfamiliarity w i t h the draftingD l position could possible explain w h y no changes i n heart rate were observed as anticipated. Additional factors which may have influenced results include the constraints imposed by the testing apparatus. It is possible that the face mask leaked environmental air during both or one of the trials, although the data does not suggest that this occurred and the face mask was fitted very securely to the subject.  The weight of the equipment could have affected the  subjects  biomechanics. The subject d i d report that the equipment felt very constricting and difficult to breath with. This could also have affect the subjects physiology especially heart rate and respiration. M o u t h pieces and face masks are k n o w n to influence breathing pattern (Loring et. al. 1990) although r u n n i n g style is  76  O  L  o  o  L  o  o  m  o  i  n  o  L  o  o  T I M E (sec)  F I G U R E A2: Heart rate response to running in leading and drafting positions.  77  O  L  o  o  L  o  o  L  o  o  m  o  L  D  o  T I M E (sec)  F I G U R E A.3:  Oxygen consumption response to running i n leading and drafting positions.  78  O  L  o  o  m  o  L  o  o  L  o  o  L  o  o  T I M E (sec)  F I G U R E A4:  Minute ventilation response to running in leading and drafting positions.  79  generally unaffected at submaximal running speeds (Siler et. al. 1993). The main difficulty presented by the Cosmed K 2 face mask is that it could have altered the subjects breathing pattern and may have affected his performance d u r i n g the trials as a consequence.  For this subject at least,  the face mask could have  hindered performance making it more difficult to evaluate the effects of drafting on the subject while running without the testing apparatus.  From this study, it was determined that using portable equipment outdoors had some definite disadvantages. It d i d however permit the first glimpse at the effects of drafting i n a outdoor road race environment. A 29.0 % reduction i n oxygen consumption, and 18.7% reduction i n minute ventilation was found when a elite level distance runner drafted directly behind another runner. This case study suggests that drafting, running i n the aerodynamic shadow of another runner, can reduce oxygen consumption and minute ventilation, and thus energy expenditure w h i l e r u n n i n g outdoors. Future studies u s i n g less constricting  equipment are recommended to further evaluate the effects of  drafting on distance runners.  REFERENCES  Loring S.H., Mead J., Waggener T.B. (1990). Determinants of breathing frequency during walking. Respir. Physiol. 82:177-188. Siler W . C . (1993). Is running style and economy affected by wearing respiratory apparatus. M e d . Sci. Sports Exerc. 25(2): 260-264.  80  APPENDIX 3 PILOT S T U D Y  The effects of drafting on highly trained distance runners. V . Corvalan-Grossling, J. Taunton, D. Clement, D. McKenzie, K. Coutts School of H u m a n Kinetics , The University of British Columbia  ABSTRACT The metabolic responses to running at 4.47 m/s directly behind another runner (drafting) were studied i n eight trained male distance runners. consumption  Oxygen  (VO2), carbon dioxide p r o d u c t i o n (VCO2), and minute  ventilation (VE) were estimated from a 1 minute sample of expired air collected immediately after a 1.2 mile run. Heart rates were monitored every 15 seconds during all performances. Perceived exertion was measured using the Borg scale at the end of the expired air collection. Subjects were randomly assigned configurations. A recovery period of 15 minutes was between all performances. minute  allowed  Drafting significantly reduced post-exercisei-  VO2 15% (1.33 ± 0.25 vs. 1.57 ± 0.34 L/min), VCO2 22% (1.10 ± 0.30 vs.  1.41 ± 0.49 L/min), V E 17% (41.3 ± 8.5 vs. 49.9±13.8), and rating of perceived exertion 11% (10 ± 0.4 vs. 11 ± 0.4) (p < 0.01). Heart rates were not significantly different between the two trials. These results showed that running i n the aerodynamic shadow of another runner could be very advantageous for distance runners and that coaches should expose athletes to drafting situations in training so that athletes can practice this energy-saving strategy. Coaches  81  must also be aware that athletes who consistently run within a pack or drafting are not obtaining the full benefits of their training.  82  INTRODUCTION In any endurance running event, optimum performance is generally achieved by efficiently utilizing the available energy. The longer the distance of a race, the more important the conservation of energy becomes. This concept implies that having a high capacity for p r o v i d i n g the exercising muscles w i t h energy is extremely important and that being able to maintain a h i g h r u n n i n g speed without negatively affecting the rate of utilization of total energy sources is also critical.  Aerodynamic drag is a major source of energy expenditure i n many sports, particularly d o w n h i l l skiing, ski jumping, the luge, bobsledding, speed skating, and cycling, where high velocities are reached (Halliday et al. 1988, K y l e et al. 1984). Efforts to reduce aerodynamic drag result i n decreased energy cost and improved performance. Aerodynamic drag is estimated to cost distance runners between 2-13% of their total energy (Davies 1980, H i l l 1928, P u g h 1970, P u g h 1971). The energy cost of running at a constant velocity increases as aerodynamic drag increases (Costill 1979).  Aerodynamic drag occurs for two reasons. One, the pressure that results from air molecules striking a surface and bouncing off, undergoing momentum changes and exerting normal forces on the surface. The other type of force, air friction, arises from the sliding motion of air molecules along the surface as they collide w i t h rough surfaces. A i r flow can be either laminar or turbulent, depending on many factors such as relative speed, surface roughness, and the type of surface material (Halliday et al. 1988, Olsen et al. 1987). A t slow speeds the flow of air molecules w i l l be laminar, this results i n quite low drag forces. A s the relative speed of the air and the surface increase, the laminar flow becomes unstable and  83  layers of air begin to separate. The flow then becomes turbulent, characterized by whirling eddies of air. Turbulent boundary layers have m u c h higher drag than laminar layers. However, the highest aerodynamic drag is caused by instability at air velocities i n the transition region between laminar and turbulent flow (Birkhoff 1960, Halliday 1988). The aerodynamic drag can be five times greater in the transition speed ranges than the aerodynamic drag for the purely turbulent flow. Therefore, it follows that to achieve l o w drag forces this transition region must be avoided. The transition region has been estimated to occur at speeds of about 4-6 m / s for an upright cyclist (Tipler 1990). Considering the similarities i n geometry and drag coefficients between cyclists and runners (Pugh 1976), the transition region w o u l d theoretically occur at the same speed range of 4-6 m / s for runners.  The relative velocity of the air on the track or road is rarely zero. W h e n running in a tail w i n d , the aerodynamic drag w i l l provide a forward force. A head w i n d , on the other hand, w i l l provide a retarding force as it increases the aerodynamic drag. It has been estimated by Dapena et al. (1987) that a 2 m / s tail w i n d can give a 100 m sprinter a 0.07 second advantage; while, a 2 m / s head w i n d can result i n a 0.085 second disadvantage. It appears that the hindrance produced by a head w i n d is larger than the time aid produced by a tail w i n d of the same intensity. Another factor w h i c h is relevant to distance runners, a group of athletes w h i c h tend to have similar physique - tall, light, and lean - is that the times of tall light athletes are more sensitive to changes i n w i n d conditions, aerodynamic drag, than those of short and heavy athletes (Dapena et al. 1987). Distance runners, moreover, race i n the 4.5-6 m / s speed range w h i c h is theoretically associated w i t h the highest drag forces. Aerodynamic drag should be a concern for elite level distance runners.  84  Typical strategies employed by runners to reduce their aerodynamic drag are to reduce their coefficient of drag by using smooth spandex cloth, modified shoes, and head gear. W i n d tunnel tests of clothing, hair, and shoes show that it is possible  to reduce the aerodynamic drag of a runner by 0.5 % to over 6 %  (Adrian et al. 1989, Kyle et al. 1986). Reducing frontal area and thus exposure to aerodynamic drag is easily accomplished by athletes i n other sports. Cyclists lean forward until their backs are horizontal and their arms are tucked tightly against their bodies. Skiers can crouch d o w n over their skis into the "egg" position until they are practically sitting on their ankles. Speed-skaters bend their upper bodies 90 degrees so they are parallel to the ground. Runners are limited i n their postural adjustments but can decrease their frontal area by using tight fitting clothing and by trimming or covering their hair.  A strategy that could reduce the aerodynamic drag forces on runners is drafting. This technique is commonly applied i n cycling, skiing, and other h i g h drag sports. M a n y investigators and runners have recommended the tactic or running in the aerodynamic shadow of another runner, p r i m a r i l y based on anecdotal information and the results obtained from investigations on the effects of drafting i n other sports ( H i l l 1928, Kyle 1979, Kyle 1979a). O n l y two studies have investigated this topic, but only one has been conducted on a runner (Pugh 1971). To date, the effects of drafting and running have only been cursorily examined.  The purpose of this study was to investigate h o w drafting, r u n n i n g i n the aerodynamic shadow of another runner, affected specific physiological variables and  perceived  exertion. These  p h y s i o l o g i c a l variables  were:  oxygen  consumption, carbon dioxide production, minute ventilation, and heart rate.  85  These physiological variables have been found to be h i g h l y correlated to performance (Cavanagh 1990, Conley et al. 1980, Daniels 1985); thus, if drafting reduces oxygen consumption, carbon dioxide production, minute ventilation, and heart rate, it is more than likely to improve performance by permitting an athlete to increase his/her maximum sustainable speed.  T w o different running positions were tested, drafting and leading. Runners' perceived exertion was measured i n order to examine if drafting reduced the rate of perceived exertion and if it corresponded w i t h changes, if any, i n the physiological variables. The study was composed of one experimental test, and one maximal aerobic power test. The protocols followed for both portions of the study are described below.  METHODS Subjects Eight h i g h l y trained, male runners  volunteered  to participate  i n this  investigation. Seven were intercollegiate long distance runners, and one was a former competitive s w i m m e r / n o w marathoner. By self-report, each subject was competing i n distance events ranging from 5000 m to marathon distances, was actively training i n excess of 40 k m of distance running a week for at least one year, had completed a mile run in a time of 5 minutes or less within 2 months of his p a r t i c i p a t i o n i n the  study, and was  apparently  healthy  with  no  musculoskeletal complaints or documented history of cardiorespiratory disease. A l l subjects were fully informed of the risks and potential discomfort associated w i t h the testing procedures before giving their signed, informed consent, as required by the Behavioral Sciences Screening Committee for Research Involving H u m a n Subjects at the University of British Columbia. The subjects had the  86  following characteristics: age, 25 + 6 yr. (mean + SD); height, 169.8 ± 8.9 cm; mass, 64.9 + 7.5 k g (see Table A l ) . U s i n g a large and diverse group of distance runners as subjects w o u l d have made the results of this investigation more generally applicable. In this study, the response of a specialized subgroup, elite distance runners, was examined to diminish the effects of confounding variables such as training effects and changing biomechanics.  Since individuals in this study were competitive distance runners, there existed the possibility that the prolonged maximal performance required i n competition may have affected their running economy and running mechanics during testing (Cavanagh 1990); however, recent evidence suggests that a training run or 10 k m race does not produce a significant increase in the aerobic demand of running or the gait pattern i n subsequent short-term, submaximal runs (Morgan 1990). To minimize these effects, subjects were tested at least three days after competing i n a racing or strenuous training session.  Procedures i n the laboratory M a x i m a l oxygen consumption ( V 0 2 m a x ) was assessed u s i n g a m o d i f i e d continuous treadmill r u n n i n g protocol.  Prior to testing the purpose and  procedure of the test were clearly explained to the subjects prior to the test, as was the test objectives and the criteria at which the test was terminated. Subjects were required to report to the laboratory i n a three hour post-prandial state and have refrained from strenuous physical activity during the day of the test. The subjects had their height and weight taken.  Body weight included that of  clothing since it w o u l d contribute to the workload. Height was measured w i t h shoes removed.  87  TABLE A l Subject Characteristics Subject  Age  Mass (kg)  Heighh (cm)  93 94 95 96 99 100 101 102  27 24 34 24 24 18 19 32  59.0 72.0 59.4 65.8 67.9 59.0 59.0 78.0  162.0 173.0 166.2 178.0 179.8 160.0 160.0 175.0  Mean Std.Dev.  25 6  65.0 7.2  169.3 8.2  * Subjects were unavailable at the time of testing.  88  VC>2 (ml/min/kg) max  69.0 88.0 64.8 53.7 56.3 59.5 64.5 13.8  Practice Session: Subjects w h o had never run on a treadmill or undergone a V 0 2 m a x Test underwent a practice session. The purpose of the practice session was to accustom the subject to running on a motorized treadmill. After allowing the subject to warm-up on the treadmill and stretch according to personal preference, subjects performed a practice run of at least 15 minutes duration at a speed of 2.24 m / s and on 0% grade. In addition, five of the six subjects tested returned for a second test 3 weeks after the first session.  Testing Session: Expired gases were sampled w i t h the C P X - D analyzers and recorded by the M e d i c a l Graphics computer system. Heart rate was collected w i t h a portable Polar H R unit. The test was conducted on a Quinton treadmill. The subject was first equipped w i t h the belt E C G and pneumotach. The subject warmed-up for a period of 5 minutes on the treadmill at 2.24 m / s and 0 % grade. Treadmill speed was then increased to 3.13 m / s after 1 minute w i t h 0.22 m / s increases i n velocity every 1 minute until physiological or volitional fatigue. A t the 4.47 m / s and 5.36 m / s speeds, the subject ran for 2 minutes instead of 1 minute before the speed was increased by 0.22 m / s . The test was terminated when the subject met at least two of the following criteria: a) the point at which the subject voluntarily indicated fatigue (by grasping the treadmill's handrails or beginning to decrease cadence), b) a plateau i n V 0 2 , c) a respiratory exchange ratio > 1.10.  89  Procedures in the field Both trials of the experiment were conducted for each subject at the same time of the day to minimize circadian rhythm effects. The test site was a flat (0 % grade), oval, 0.4 mile concrete indoor corridor under constant environmental conditions. Athletes were randomly assigned the order of testing on the test day.  Practice Session: The purpose of the practice session was to accustom the subject to running on the test site course and testing procedures. After allowing the subject to warm-up and stretch according to personal preference, a practice run at a speed less than 3.57 m / s for at least 15 minute duration was performed. Subjects were asked to practice forming the different configurations during the run. Subjects were either tested at the end of this session or on the next day at the same time. A l l athletes were required to take at least 15 minutes rest between test trials and the practice session until H R was at resting levels.  Testing Session: After warming-up for at least 5 minutes and running 1 lap at 3.57 m / s , the subject was instructed on the configuration w h i c h was to be used for that trial. The subject was then be equipped w i t h a portable Polar H R unit, Vantage X L . In the first lap (0.40 mile), the subject reached the experimental speed of 4.47 m / s and continued running at this 6 minute mile pace for the next two laps (0.8 mile). A t the end of the third lap, the subject stopped running and was quickly equipped w i t h a face mask connected to a meteorological balloon. A 1 minute air sample was collected. Following the air collection, the subject was asked to rate his perceived exertion using the Borg scale. After a fifteen minute recovery period the procedure described above was repeated for the second configuration. Both configurations were tested on the same day. One subject was tested twice on consecutive days w i t h identical results.  90  A l l trials were conducted on the same section of the course w i t h the subject running i n the same direction. A pace cyclists equipped w i t h a CatEye M i t y 2 cycle computer rode closely behind the runners, recording time, distance, speed, and indicating verbally to the test group if they should adjust their pace or position throughout the experiment to ensure that warm-up and trial paces and positions were reached and maintained. A i r samples were analyzed a m a x i m u m of 5 hours post collection. Oxygen and carbon dioxide fractions were determined using Beckman oxygen and carbon dioxide analyzers (Fullerton, U S A ) calibrated w i t h gases of k n o w n concentrations. Sample volumes were measured i n a Tissot spirometer.  Running configurations tested  L e a d i n g - N D was the control configuration. Drafting-1 was the experimental position. In position D I the subject ran directly behind another runner. A l l eight subjects were tested i n these two positions, N D and D I , at the six minute mile pace (4.47 m / s ) . Another two of the eight subjects (100, 101) were tested i n two additional positions, D2 and B2; while a third subject (102) was tested i n the diamond configuration, D 3 . D2 had the subject drafting on the inside of a triangle w i t h one runner i n front and another runner beside h i m on the outside i n position B2. D3 had the subject drafting behind a group of three runners as shown i n Figure A 5 . In the drafting trials, the subject was 1 meter or less behind the leading runner. These conditions were maintained throughout the entire trial.  Experimental design and statistical analysis of data.  The independent variable i n this study was Position (factor 1 w i t h 2 levels: leading-ND and drafting-Dl). The dependent variables for this study were V O 2 ,  91  ©  FIGURE A5:  (I  D2)  Running Configurations. N D - Leading D = Drafting  92  V C O 2 , V E , H R , and R P E . The statistical analysis used to investigate the effect of drafting o n V O 2 , V C O 2 , V E , H R , and R P E were 5 paired t-tests. The level of significance was p< 0.05. RESULTS The percent reduction i n post-exercisei-minute V O 2 , V C O 2 , V E , and R P E resulting from drafting behind a single runner at 4.47 m / s were 15%, 22%, 17%, and 1 1 % respectively (see Figure A 6 ) . Post-exercisei-minute V O 2 , V C O 2 , V E , as well as, R P E were significantly reduced after drafting behind a single runner (p < 0.01). Post-exercisei-minute heart rate was reduced only slightly, 1.5%, w h e n subjects drafted behind a single runner i n the D I position. M e a n values are shown i n Table A 2 .  The post-exercisei-minute V O 2 for subjects 100 and 101 was reduced from 1.63 L / m i n and 1.56 L / m i n w h e n they lead to 1.48 L / m i n and 1.26  L/min  respectively w h e n they drafted i n the B2 position and to 1.38 L / m i n and 1.19 L / m i n w h e n they drafted i n the D 2 position. Their drafting-Dl values were 1.45 L / m i n and 1.17 L / m i n . Similar trends were observed for post-exercisei-minute V C O 2 and V E . RPE values were the same for leading-ND and B 2 , while draftingD l and D 2 R P E values were the same but lower for both subjects (see Table A3). Drafting i n positions B2 and D 2 produced very similar physiological results to the values for drafting behind a single runner, D I . Position D 2 seems to be slightly more favorable for these two subjects than B 2 (see Table A 3 ) . Postexercisei-minute V O 2 for subject 102 was reduced from 2.16 L / m i n leading to  93  30 r25 L •J3 0>  20 15 h  10 U 5 P  02  FIGURE A6:  C02  VE  HR  RPE  Reduction in oxygen consumption, carbon dioxide production, minute ventilation, heart rate, 'and R P E resulting from drafting directly behind another runner. * Significantly different from that while leading (p< 0.05).  9 4  TABLE A2 One minute post-exercise oxygen consumption, carbon dioxide production, minute ventilation, and heart rate values in leading and drafting positions.  Position  V O 2  V C O 2  (1/min)  VE (1/min)  HR (beats /min)  RPE  (1/min) Leading  1.57 ± 0 . 1 2  1.41 ± 0 . 1 7  49.9 ± 4 . 9  115 ± 4  11.0 ± 0 . 4  Drafting  1.33 ± 0.09  1.10 ± 0.11  41.3 ± 3 . 0 *  111 ± 6  10.0 ± 0 . 4 *  A l l values are mean ± std. dev. * Significantly different from leading trial.  95  TABLE A3 One minute post-exercise oxygen consumption, carbon dioxide production, minute ventilation, and heart rate values for subjects w h o were tested i n additional drafting positions.  Subject. No.  Position  VO2  VCO2  (1/min)  VE (1/min)  RPE  100  ND DI D2 B2  1.63 1.45 1.38 1.48  1.57 1.04 1.16 1.29  4.70 4.42 3.16 3.46  13 12 12 13  101  ND DI D2 B2  1.56 1.17 1.19 1.26  1.60 1.08 1.09 1.11  5.83 3.82 3.34 3.64  13 10 10 13  102  ND DI D3  2.16 1.64 1.86  2.23 1.58 1.75  6.22 4.25 4.94  12 11 10  (1/min)  96  1.64 L / m i n i n position D I and to 1.86 L / m i n i n position D3 (see Table A 3 ) . Similar trends were also observed for post-exercisel-minute VCO2 and V E . R P E was the lowest for D3 w i t h a value of 10, second lowest for D I w i t h a value of 11, and 12 for N D .  DISCUSSION Considering that at the critical, velocity range between 4-6 m / s , the estimated transition region between laminar and turbulent air flow, and speeds at w h i c h elite distance runners compete in, it is possible that the energy expenditure and therefore running economy are markedly altered by the aerodynamic drag forces which an athlete encounters. P u g h (1971) examined what w o u l d happen to the running economy when a runner drafted behind another runner. H e found from the result of a single case study that drafting, running about 1 m behind another runner, virtually eliminated air resistance and reduced oxygen consumption by 6.5 % w h e n r u n n i n g at 4.5 m / s w i t h a w i n d velocity of 6 m / s .  This is  approximately an 80 % reduction i n the energy cost of overcoming air resistance. P u g h then measured the dynamic air pressure around the runner w i t h a Pitostatic tube. The pressure was negative 0.6 m behind the runner and still relatively low 1 m behind the runner. A t the positions slightly to the side-behind the runner, the pressures were almost the same as the pressure 2 m i n front of the runner. Pugh's pressure results are useful for determining w h i c h drafting positions may be most effective. They suggest that drafting directly behind a runner may be more effective than to be i n the position slightly to the sidebehind a runner. The results of our investigation clearly found that drafting as close as possible, approximately 1 m , behind another runner of the same or larger physical build reduced post-exercisei-minute oxygen consumption, carbon dioxide production, minute ventilation, as w e l l as, perceived exertion. It is  97  interesting that i n the data collected from two of our runners i n additional positions, drafting i n positions slightly to the side-behind the leading runner with another runner at the subject's side produced similar reductions in the postexercisei-minute physiological parameters as those observed d u r i n g drafting trials where the subjects were directly behind a shield runner.  The only additional evidence available i n the running literature that indicates that drafting can reduce a runner's aerodynamic drag was found i n a study conducted on cyclists by K y l e (1979). Based on his results on upright cyclists coasting i n a 200 m hallway, Margaria's data (1963) for the rate of energy consumed during running in still air, and the assumption that drag coefficient for the upright position i n cycling was equivalent to that of runners, K y l e predicted that drafting w o u l d improve running economy by 4 % when drafting 1 m behind another runner at 6 m / s .  A l t h o u g h this value has meaningful practical  implications, it is lower than that obtained by P u g h (1971) and much lower than our results for post-exercisei-minute oxygen consumption when drafting directly b e h i n d another runner at 4.47 m / s .  M e t h o d o l o g i c a l and computational  differences could account for the discrepancy. However, another reason for the difference may result from the assumption made on the value of the coefficient of drag. The values estimated by other investigators vary considerably from those used by Kyle (Pugh 1976, Shanebrook et al. 1976). In general, estimations of the coefficient of drag for runners have several inherent problems. One, the coefficient of drag has been calculated for a runner i n a passive state and i n Kyle's study a passive cyclist in an upright position. The assumption that the coefficient w o u l d be the same for a m o v i n g runner ignores the possible effects that the motion of body segments relative to each other may have on the net aerodynamic drag. Moreover, an upright cyclist may not have the same body  98  position to a m o v i n g runner. Another problem, w h i c h may also affect the estimations for aerodynamic drag energy cost, is that even in still air both the ground and the air molecules move backwards relative to the runner. This may affect the airflow and consequently the aerodynamic drag.  The majority of the research on drafting's effects on aerodynamic drag, energy expenditure, and performance has been conducted on cyclists. In Kyle's (1979) investigation on the effects of drafting on cycling power output and w i n d resistance i n a variety of positions, he found that drafting directly behind another rider reduced the air resistance by 44 % irrespective of the number of riders in the pace line. W h e n a rider drafted i n the center of a tightly packed cluster of riders the air resistance was surprisingly only reduced by 24 %; however, this effect was investigated i n a single test. Kyle also reported that air resistance was only reduced by 23 % when the rider drafted i n a position slightly to the sidebehind instead of directly behind another rider. A s w o u l d be expected from Pugh (1971) and Shanebrook et al. (1976) pressure data, he found the reduction i n air resistance increased the closer a rider drafted behind another rider. M c C o l e et al. (1990) conducted a similar study to Kyle's.  They measured  energy  expenditure, oxygen consumption of competitive cyclists on a flat stretch of straight road w h i l e drafting.  They reported an 18 % reduction i n oxygen  consumption at 8.89 m / s and a 27 % reduction i n oxygen consumption at 10.28 11.11 m / s for subjects drafting behind one rider. Drafting 1, 2, 3, or 4 riders in a line resulted in the same reduction of oxygen consumption, while drafting within a group of 8 riders at 11.11 m / s reduced oxygen consumption by 39 %. The latter results on the effect of drafting behind a pack of riders conflicts w i t h Kyle's (1979) observation and our o w n results for position D3. Drafting i n the diamond configuration,  D 3 , reduced  the  subjects  99  post-exercisei- i te m  nu  oxygen  consumption by 14%. While drafting in directly behind a shield runner reduced his post-exercisei-minute oxygen consumption by 24%. Similar trends were found when comparing the other physiological parameters. Perceived exertion did not follow this trend.  Drafting behind a pack may turn out to improve running economy even more than running behind a single runner, but this position posses other strategic problems for runners. This position m y conserve energy and be beneficial physiologically, strategically a runner is at a disadvantage w h e n boxed i n . Chances of w i n n i n g are reduced. If the intent is to improve performance time, running w i t h a stronger group w o u l d be recommended. D u r i n g training sessions drafting and pack running should be discouraged unless the purpose is to train runners to draft.  In s w i m m i n g , drafting has been found to reduce post exercise oxygen consumption by 11 %, blood lactate.by 31 %, and rate of perceived exertion by 21 % (Basset et al. 1991). In cross -country skiing, Bilodeau et al. (1994) found that drafting significantly reduced heart rate by 5.6%, from 163 to 154 beats/min. Heart rates were not significantly different between the two trials in this study. There exists the possibility that due to the majority of the subjects inexperience w i t h drafting, heart rates may have remained elevated due to the anxiety and stress related to running directly behind a runner and trying to avoid being kicked  or k i c k i n g the  l e a d i n g runner. It is also possible  that  some  synchronization between locomotion centers and cardiovascular centers may have occurred. Breathing frequency and heart rate synchronization w i t h leg frequency during rhythmic exercise has been documented i n laboratory animals  100  and reported to occur i n cyclists and runners (Caretti et al. 1992, N i i z e k i et al. 1993).  F r o m our results it is evident that drafting directly behind another runner reduces energy consumption during the initial stages of recovery. Post-exerciseiminute measurements have been used i n previous studies to gage the effects of drafting during a s w i m m i n g trial (Basset et al. 1991); however, measurements made d u r i n g an activity w i l l always be the best method to assess and truly evaluate the effects that a particular strategy has on an athlete d u r i n g that activity. Future studies are being developed to investigate the physiological effects of drafting during trial runs in various positions w i t h the aid of a portable indirect calorimeter. The aim of these studies w i l l be to quantify the effect of drafting during trial runs and to clarifying the question of w h i c h position is the most economical for runners and w h i c h one do they perceive as being the most economical. We predict that the effects of drafting during distance running at the relative velocity of 4-6 m / s w i l l produce reductions i n metabolic energy expenditure much larger than previously estimated.  In summary, we found that drafting in distance running at a relative speed of 4.47 m / s resulted in a significant reduction i n post exercise oxygen consumption, carbon dioxide production, and minute ventilation i n the first minute of recovery, as well as, a significant reduction i n perceived exertion. The fact that these changes occurred strongly suggests that drafting is a useful technique for distance runners to evade aerodynamic drag. By utilizing this technique, an athlete could conserve energy and thus improve his or her performance toward the end of a competition. In training sessions, however, drafting and pack runs should be avoided to maximize the training benefits, unless the objective is to  101  train athletes to draft. W e found that only one of our subjects regularly drafted during races.  102  REFERENCES  A d r i a n M.J., Cooper J . M . (1989). Biomechanics of H u m a n Movement. Benchmark Press, Inc., Indianapolis, pp. 439-466. Basset D . 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