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Instantaneous cardioacceleration in response to high-intensity, short-duration isometric contractions Kitagawa, Eiji 1976

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INSTANTANEOUS CARDIOACCELERATION IN RESPONSE TO HIGH-INTENSITY, SHORT-DURATION ISOMETRIC CONTRACTIONS by E i j i Kitagawa B.P.E., University of British Columbia, 1970 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF PHYSICAL EDUCATION in the School of Physical Education and Recreation We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1976 ( 6 ) E i j i Kitagawa In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced d e g r e e at t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . -Dopo N:-mefrt—of- School o f Physical Education and Recreation The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, Canada Date RRptRTDhBr 1 1 . 1 9 7 6 i ABSTRACT The purpose of this study was to investigate on a beat-by-beat basis, the nature of the instantaneous cardioacceleration resulting from short-duration, high-intensity, isometric contractions; to determine the relationship between relative muscular tension and cycle time, actual c change in cycle time and relative change in cycle time; and to determine the effect of short-duration, high-intensity, isometric contractions on the recovery rate.of cycle time. Muscular tensions and electrocardio-grams were recorded before, during and after the isometric task and relative muscular tension, cycle time, actual change in cycle time and relative change in cycle time were calculated from these recordings. The sample population consisted of thirty university males. Each subject was randomly assigned to one of three groups. The task consisted of either a 50% MVC, 75% MVC or 100% MVC to be held for 10-seconds. Dynamometer and ECG recordings were monitered for the 15-seconds immediately before the contraction, the 10-seoonds during the contraction and the 15-seconds immediately following the contraction. The hypotheses were: at the onset of an isometric contraction, the i n i t i a l rate of increase of the relative change in cycle time i s directly related to the magnitude of the percent maximal voluntary con-i i traction; during the isometric contraction, the relative muscular tension i s more closely related to the relative change in cycle time than either cycle time or actual change in cycle time; and, upon release of the iso-metric contraction, the i n i t i a l rate of decrease of the relative change in cycle time is directly related to the magnitude of the percent maximal voluntary contraction. The trend analysis of the relative change in cycle time, during contraction, indicated that the linear and quadratic trends were different between the three groups. However, trend analyses of paired comparisons between the three groups indicated that the trends of the 50% MVC and 75% MVC groups were significantly different from the trend of the 100% MVC group, but, were not significantly different from each other. The post-hoc Newman-Keuls analysis indicated that the heart responded differently over the f i r s t five beats than over the last five beats, suggesting that there are at least two phases in the cardio-acceleratory response to isometric contractions and these two phases may be a result of a central and a peripheral heart-trigger mechanism. The trend analysis of the relative change in cycle time, during recovery, indicated a significant linear trend in beats with a significant difference in this trend between groups. However, observa-tion of the graphic plot of means indicated that the data did not support i i i the hypothesis, that the i n i t i a l rate of decrease of relative change in cycle time was directly related to the magnitude of the ZMVC. The non-support may have been due to the masking effect of respiration. i v ACKNOWLEDGMENTS The author would like to express his sincere gratitude to the following people: Dr. Kenneth Coutts, committee chairman, and Dr. Robert Schutz for being physiological and s t a t i s t i c a l mentors, respectively, during his Master's programme; Dr. Michael Patterson for his stimulation and support in cardiological matters; and, last but by no means least, Mr. Chiu and, my wife, Robin for their inval-uable assistance during the data collection. Furthermore, the author's Master's degree would not have been as easily attainable without the financial, emotional and moral support of his wife. V TABLE OF CONTENTS Chapter Page I. STATEMENT OF THE PROBLEM 1 Introduction 1 Problem 3 Subproblems • 3 Hypotheses 3 Definition of Terms. , 4 Assumption 7 Limitations . <• 7 Justification 8 II. REVIEW OF THE LITERATURE 9 Introduction 9 Minimal-Duration Studies..... 9 Short-Duration Studies 10 Long-Duration Studies . 13 Peripheral Heart Trigger Mechanism(s) 15 Summary 19 III. MATERIALS AND METHODS 20 Experimental Design. 20 Subjects........ 20 Experimental Procedure 20 Preparation... 22 v i Chapter P a 8 e 100% MVC Determinations 22 Commands and Instructions 23 Data Recording • •• 24 S t a t i s t i c a l Analyses •• 25 Resting Condition 30 Contraction Condition . 30 Recovery Condition . • 31 IV. RESULTS AND DISCUSSION 32 Results 32 Resting 32 Contraction 37 Recovery 39 Discussion .... 59 Resting 59 Contraction 60 Recovery 64 V. SUMMARY AND CONCLUSIONS 66 Summary 66 Conclusions 68 BIBLIOGRAPHY 69 APPENDICES 72 A. Individual Raw Scores 72 B. Individual Computed Scores...... 82 v i i Chapter Page C. ANOVA Paired Comparisons of RCCTC for the Three Levels of %MVC 93 D. Recovery Condition - Means and Standard Deviations of Cycle Time and Actual Change in Cycle Time with Graphical Presentations 97 v i i i LIST OF TABLES Table P a S e I Relationship between Cycle Time and Heart Rate.... 26 I I Resting Condition - Means and Standard Deviations of Cycle Time 33 I I I Summary of ANOVA for Resting Condition - Cycle Time 35 IV Newman-Keuls Analyses f o r Resting Condition - Cycle Time 36 V Contraction Condition - Means and Standard Deviations of Relative Muscular Tension 40 VI Summary of ANOVA for Contraction Condition - Relative Muscular Tension 42 VII(A) Newman-Keuls Analyses for Contraction Condition -Relative Muscular Tension 100% MVC Group 43 VII(B) Newman-Keuls Analyses for Contraction Condition -Relative Muscular Tension 75% MVC Group 44 VII(C) Newman-Keuls Analyses for Contraction Condition -Relative Muscular Tension 50% MVC Group 44 VIII Contraction Condition - Means and Standard Deviations of Relative Change i n Cycle Time... 45 IX Summary of ANOVA for Contraction Condition - Relative Change i n Cycle Time... 47 X(A) Newman-Keuls Analyses for Contraction Condition -Relative Change i n Cycle Time 100% MVC Group 48 X(B) Newman-Keuls Analyses for Contraction Condition -Relative Change i n Cycle Time 75% MVC Group 49 X(C) Newman-Keuls Analyses for Contraction Condition -Relative Change i n Cycle Time 50% MVC Group.. 49 ix Page Contraction Condition - Means and Standard Deviations of Cycle Time ' Summary of ANOVA for Contraction Condition -Cycle Time ••• Contraction Condition - Means and Standard Deviations of Actual Change in Cycle Time Summary of ANOVA for Contraction Condition - Actual Change in Cycle Time Recovery Condition - Means and Standard Deviations of Relative Change i n Cycle Time Summary of ANOVA for Recovery Condition - Relative Change i n Cycle Time X LIST OF FIGURES Figure Page 1 Experimental Design 21 2 Graphical Presentation of the Relationship between Cycle Time and Heart Rate 27 3 S t a t i s t i c a l Design. 29 4 Graphical Presentation of Cycle Time during the 10 Resting Heart Beats 34 5 Graphical Presentation of Relative Muscular Tension during the 10 Contraction Heart Beats 41 6 Graphical Presentation of Relative Change i n Cycle Time during the 10 Contraction Heart Beats 46 7 Graphical Presentation of Cycle Time during the 10 Contraction Heart Beats 51 8 Graphical Presentation of Actual Change in Cycle Time during the 10 Contraction Heart Beats. 54 9 Graphical Presentation of Relative Change in Cycle Time during the 10 Recovery Heart Beats.. 57 1 CHAPTER I STATEMENT OF THE PROBLEM Introduction To date, the majority of physiological investigations on the heart rate response to exercise have been concerned with dynamic, steady-state exercises of varying degrees of intensity in variable environments (Rowell, 1974) . Until recently, only a few investigations have studied the effect of static (isometric) exercise on the heart rate response. These investigations f a l l into two general categories, according to the nature of the cardiovascular response studied: (1) studies of the i n i t i a l cardiovascular response; and (2) studies of the pressor response and i t s related cardioacceleration. The category (1) studies required contractions to be held for 1-second or less and analyzed cycle time on a beat-by-beat basis; whereas, category (2) studies involving contractions of more than 1-seconds duration either reported maximal change i n heart rate (beats/min.) or reported heart rate (beats/min.) at 10- to 30-second intervals. A study by Tuttle and Horvath (1957) indicat es that the major portion of cardioacceleration occurs within the f i r s t 15-seconds of a maximal voluntary contraction (100% MVC) held for 1-minute. Flessas et a l . (1970) compared a time-based and a beat-by-beat analyses of heart rate during a 12-second Valsalva Maneuver (VM) and found that the beat-by-beat analysis resulted in a smaller coefficient of v a r i -ation through a l l phases of the maneuver. Studies by Paulev (1973), Humphreys and Lind (1963), and Freyschuss (1970b) reported d i f f i c u l t y i n detecting a relationship between the change in heart rate and the percent maximal voluntary contraction (% MVC) i n the range 50% MVC - 100% MVC. Recent s t a t i s t i c a l studies by Khachaturian and Kerr (1972) and Jennings et a l . (1974) suggest that cycle time i s a more effective measure to use i n the analysis of evoked cardiac responses, than heart rate (beats/min The study by Tuttle and Horvath (1957) indicates that the major portion of cardioacceleration, in response to an isometric contraction, occurs in a time span of more than 1-second, but less than 15-seconds. Unfortunately, the category (1) studies were of too short a duration to determine the time course of the change in cardioacceleration and the category (2) studies tended to mask the time course of the change in cardioacceleration by summing the heart beats over 10- to 30-second intervals. I f , the findings of Tuttle and Horvath (1957) were to be considered in conjunction with the results of Flessas et a l . (1970), Khachaturian and Kerr (1972), and Jennings et a l . (1974), i t would seem reasonable to assume that a beat-by-beat analysis of cycle time, during a 10- to 15-second contraction, should lead to a better under-3 standing of the relationship between relative muscular tension and the resulting cardioacceleration. In fact, an experiment of this nature may detect a relationship between the change in heart rate and the per-cent maximal voluntary contraction in the 50% - 100% MVC range. Problem The purpose of this study i s to investigate, on a beat-by-beat basis, the nature of the instantaneous cardioacceleration resulting from short-duration, high-intensity, isometric contractions. Subproblems 1. To determine the relationship between relative muscular tension and cycle time, actual change in cycle time, and relative change in cycle time. 2. To determine the effect of short-duration 50%, 75%, and 100% maximal voluntary contractions on the recovery rate of cycle time. Hypotheses 1. At the onset of an isometric contraction, the i n i t i a l rate of increase of the relative change in cycle time (RCCTC) is directly related to the magnitude of the percent maximal voluntary contraction (%MVC). 4 2. During the isometric contraction, the relative muscular tension (MT ) i s more closely related to the relative change i n cycle K time (RCCT^) than either cycle time (CT^) or actual change in cycle time (ACCT C). 3. Upon release of the isometric contraction, the i n i t i a l rate of decrease of the relative change in cycle time (RCCT ) i s directly related to the magnitude of the percent maximal voluntary contraction (Z MVC) prescribed for the contraction condition. Definition of Terms Heart Beat. In the strictest sense, a heart beat consists of a t r i a l and ventricular systole. For the purpose of this study, the peak of the R-wave was used as the reference point for any given heart beat. Resting Condition. This condition consisted of the 10 heart beats immediately preceding the f i r s t heart beat in the contraction condition. Contraction Condition. This condition consisted of the f i r s t 10 heart beats after the onset of contraction. The R-wave immediately following the onset of contraction was considered as the f i r s t heart beat of the contraction condition. The onset of contraction was determined as Being that point at which the dynamometer recording pen noticeably deflected 5 from the baseline. Recovery Condition. This condition consisted of the f i r s t 10 heart beats after the point of release of the dynamometer. The f i r s t R-wave after the point of release was considered as the f i r s t heart beat of the recovery condition. The point of release was determined as being the inflection point on the dynamometer recording paper. Cycle Length. The distance between the peaks of two consecutive R-waves on an electrocardiogram (ECG). Often referred to as cardiac cycle length, R-R interval, or P-P interval. Cycle Time (CT). Cycle length expressed in milliseconds. The conversion depends on the speed of the ECG recorder. For example, at a recording speed of 100 mm./sec: Cycle Time (msec.) = Cycle Length (mm.) x 10 The cycle time immediately preceding an R-wave was taken to be the cycle time for that given heart beat. Actual Change in Cycle Time (ACCT). The control cycle time (CT ) for a given subject minus his cycle time in the contraction condi-v*Li tion (CT,,) or in the recovery condition (CT^)• 6 Contraction: ACCTC (msec.) = CT C L (msec.) - CT C (msec.) Recovery: ACCT (msec.) = CT„T (msec.) - CT (msec.) Relative Change in Cycle Time (RCCT). The actual change in cycle time (ACCT) for a given subject i n the contraction condition (ACCTC) or in the recovery condition (ACCT ) expressed as a percentage of his R control cycle time (CT ). • * ACCT„ (msec.) . n n Contraction: RCCTC = C x 100 CT C L (msec.) Recovery: RCCT = A C C T R x 100 CT C L (msec.) Percent/Relative Muscular Voluntary Contraction (100% MVC). The force that a subject was required to exert on the handgrip dynamom-eter (50%, 75%, or 100%) in relation to his maximal voluntary contraction. Maximal Voluntary Contraction (100% MVC). The method for deter-mining 100% MVC i s discussed in Chapter III. Relative Muscular Tension (MT„). Relative muscular tension and %MVC are synonymous. To avoid confusion, %MVC w i l l only be used i n refer-ence to the muscular tension "prescribed" for a subject or his given group by the experimenter. Since subjects cannot instantly attain and hold their "prescribed" muscular tension without some inter- and intra-individual vari-7 ab i l i t y , relative muscular tension w i l l only be used in reference to the dependent measure obtained from the subject during the testing. Relative muscular tension was determined from the calibrated recording on the cardio-graphy paper and expressed as a.percentage of the maximal voluntary con-traction, which was also determined from the paper recording. The relative muscular tension for any given heart beat was determined by using the peak of the preceding R-wave as the afbritrary reference point. Assumption The underlying assumption for hypothesis (1) i s that a l l three groups w i l l have equal response times in terms of attaining their prescri-bed %MVC's. A post-hoc analysis was done to determine the valid i t y of this assumption. Limitations The study i s limited by the sample size of 30 subjects of the male sex between the ages of 18 - 28 years. Furthermore, the subjects were predominantly students in the School of Physical Education and Recreation at the University of British Columbia and therefore cannot be considered as a random sample of the population. 8 Justification This study w i l l lead to a better understanding of the i n i t i a l cardioacceleratory response to isometric exercise and may lead to the development of a more effective method of analyzing evoked cardiac re-sponses. Furthermore, i t may give some insight to the time course of action of the heart trigger mechanisms that have been proposed to be operating during a normal cardiovascular response to isometric exercise. 9 CHAPTER II REVIEW OF THE LITERATURE Introduction Most studies of the circulatory response to voluntary muscle contractions, commonly termed isometric or static exercise, can be class-i f i e d according to the duration of the required contraction. The.follow-ing classifications w i l l be used to present related studies: 1. Minimal-Duration Studies (less than 1-second) 2. Short-Duration Studies (1-10 seconds) 3. Long-Duration Studies (1-minute or more) Minimal-Duration Studies Petro et a l . (1970) found that a 100% MVC with the biceps re-sulted in a significant shortening of the f i r s t R-R interval following the onset of the contraction. He estimated the cardiac latency (i.e., the latency between the onset of the contraction and the cardioaccelera-tory response) to be approximately 500 milliseconds. A study by Borst et a l . (1972) shows that a 100% MVC of either the plantar flexors or masticatory muscles elicit e d a substantial R-R interval decrease (up to 18%) with no significant difference in responses between unilateral and bi l a t e r a l plantar flexion. Their results indicated 10 that a stronger contraction (relative) tended to e l i c i t a larger interval decrease, but no clear relation could be demonstrated between response magnitude and exerted force in the range 33.3% - 100% MVC. They approx-imated cardiac latency at 400 - 600 milliseconds. Paulev (1973) found that the average heart rate increments of six subjects was between 10 - 30%; and that heart rate increments were related to %MVC when the average force was below 50% MVC, but above 50% MVC the increments were f a i r l y constant. He determined cardiac latency to be 550 milliseconds and composed of the following: "The cardiac latency consisted of an intracardiac effector time (estimated as the P-R interval: 200 msec), plus a conduction period in the vagal nerve and synapse (approx. 300 msec.) and an afferent trigger period. The afferent trigger period i s so long that i t permits the operation of most heart trigger mechanisms currently pro-posed (e.g., Golgi tendon organs, cerebral origin)." Short-Duration Studies Freyschuss (1970a) obtained pre- and post-values of heart rate and aortic pressure on 10 male subjects (22 - 28 yrs.) in response to varying %MVC's (range 50% - 95% MVC, mean 73% MVC) held for 5 - 1 0 seconds. In addition, he administered atropine (parasympathetic blocking agent), phentolamine (alpha-adrenergic blocking agent) and both atropine and phentolamirie combined. In relation to the change i n values obtained under the control condition, he found that: (1) atropine significantly decreased heart rate acceleration (p<.01) and aortic pressure rise (p<.05); (2) 1.1 phentolamine did not significantly alter heart rate acceleration, but significantly decreased aortic pressure rise (p<.05); and (3) atropine plus phentolamine significantly reduced (and i n many cases abolished) heart rate acceleration (p<.01) and significantly reduced aortic pressure rise (p<„01). These findings suggest an interacting influence of symp-athetic and parasympathetic activity. Freyschuss (1970b) duplicated his previous study (1970a) except that the subjects were eight tetraplegia males (21 - 42 yrs.) having a complete transverse spinal syndrome below segments - C-^ ; who had pre-viously passed courses of physical training and rehabilitation. He found the results were not significantly different from those of healthy men after the administration of atropine and phentolamine; indicating the possi b i l i t y that the tetraplegics were unable to u t i l i z e a peripheral beta-adrenergic mechanism even though beta-adrenergic activity i s usually-associated with inotropic effects. Freyschuss (1970b) obtained control values for heart rate and aortic pressure responses to isometric exercise from six healthy males (24 - 29 yrs.). Then obtained comparative values after administering succinylcholine (neuromuscular blockade). The heart rate increase and blood pressure rise of the "intended" handgrips were 64% and 55%, respect-ively, of the values observed during performed handgrips. This suggests the prescence of a central heart trigger mechanism. 12 A l l of the preceding minimal- and short-duration studies ascribed the cardioacceleration at the i n i t i a t i o n of isometric contractions to a withdrawal of vagal tone. A r r i v i n g at t h i s hypothesis from the results of studies involving vagotomies, sympathectomies or pharmacological block-ing agents could lead to tenuous conclusions; since i t i s generally accepted that tonic a c t i v i t y usually exists i n both divisions of the autonomic system. Therefore, a satisfactory quantitative description of autonomic control must take into account the response to simultaneous a c t i v i t y i n both the sympathetic and parasympathetic nerves. On t h i s premise, Levy and Zieske (1969) studied the effect of sympathetic-parasympathetic i n t e r -action on the canine heart rate. They ischemically destroyed the CNS by l i g a t i n g the cerebral a r t e r i e s . Using a 5 x 5 f a c t o r i a l design, they stim-ulated the rig h t s t e l l a t e ganglion (0,1,2,3,4 pulses/sec.) and the l e f t c e r v i c a l vago-sympathetic trunk (0,2,4,6,8 pulses/sec.) under the appropriate combinations. They reported a pronounced negative sympathetic-parasympa-t h e t i c i n t e r a c t i o n , such that, at high levels of vagal a c t i v i t y , changes i n sympathetic a c t i v i t y had only a n e g l i g i b l e effect on heart rate. This marked attenuation or actual masking of the sympathetic influence on heart rate by a coexisting high l e v e l of vagal a c t i v i t y was reported as being c h a r a c t e r i s t i c of a l l the experiments i n the series. On the assumption that a s i m i l a r negative interaction occurs i n man, these findings indicate that vagal withdrawal must occur i n order for the sympathetic system to e f f e c t i v e l y influence heart rate. Furthermore, Toda and Shimamoto (1968) found that stimulation of the sympathetic nerves does not result i n an increased heart rate u n t i l a f t e r an i n t e r v a l of 3 - 6 seconds. I t there-13 fore may be reasonable to assume that cardioacceleration during isometric exercise is i n i t i a l l y a result of the withdrawal of vagal tone followed by sympathetic influence. Long-Duration Studies Tuttle and Horvath (1957) had nine subjects perform a 100% MVC for 1-minute. They found that at the end of 15-seconds the heart rate (93±10.0 beats/min.) was significantly greater (t=10.38, p<.01) than at the resting level (66±8.6 beats/min.). No further significant changes in heart rate were evident during the work period, although, a trend of pro-gressive increase was indicated by the following three 15-second intervals. Ten seconds after the cessation of work, the heart rate, although sli g h t l y greater (71±10.7 beats/min.), was not significantly different from the resting level (t=1.82, p>.05). Eklund et a l . (1974) reported that a 2-minute, 50% MVC dorsi-flexion of the foot increased the heart rate from 60-86 beats/min. by the end of the contraction. Lind et a l . (1964) studied four young healthy males performing handgrips of 10% MVC, 20% MVC and 50% MVC held for 5-minutes, 5-minutes, and 1 - 2 minutes, respectively. On a 30-second basis, their heart rate data indicate: a progressive rise at 10% MVC; while at 20% MVC and 50% MVC there i s a rapid i n i t i a l rise followed by a slower progressive r i s e . 14 After the abrupt cessation of the contraction the heart rate returned to resting control levels within 1-minute. They reported that the tension was closely correlated with the magnitude and rate of increase of the cardiovascular response. Donald et a l . (1967) reported a study involving a subject with syringomyelia of one arm. Separate handgrip contractions were performed at 10% MVC (5 min.), 30% MVC (3 min.) and 50% MVC (1 min.) with the affected and unaffected hand. The heart rate response of the affected hand was similar to the response of the unaffected hand for a l l %MVC's, but, notice-ably attenuated; suggesting the possibility of an impaired peripheral heart trigger mechanism. Grossman et a l . (1973) ut i l i z e d a 50% MVC handgrip of 3-minutes duration to assess the changes in the inotropic (contractile) state of the l e f t ventricle. The eight normal subjects consisted of five males and three females with an age range of 20 - 72 years. They found signi-ficant increases in aortic mean pressure (94±3.0 to 119±5.5 mm. Hg.), heart rate (79±5 to 98±8 beats/min.), and stroke work (81±8.8 to 104±11 gm. m.); but, no significant increases in l e f t ventricular end-diastolic pressure (6.8±0.8 to 7.5±1.2 mm. Hg.), and systemic vascular resistance (1606±176 to 1645±260 dynes-sec.-cm. "*). They suggest that the normal cardiovascular response to isometric exertion includes a major increase in l e f t ventricular myocardial contractility. 15 Quinones et a l . (1974) had nine subjects maintain a 25% MVC handgrip for 3-minutes and observed a significant increase (p<,01) in the isovolumic indices of l e f t ventricular contractility. In order to test i f the increase in l e f t ventricular contractility during exercise was related to the significant increase i n heart rate, they re-measured the isovolumic indices during a t r i a l pacing at a heart rate equal to the one achieved during exercise. A t r i a l pacing was associated with a sig-nificant- increase (p<.05) in a l l of the indices of contractility; however, 50% of the indices achieved with a t r i a l pacing were significantly lower (p<.05) than those achieved during exercise. They stated that; "The aug-mented indices of contractility determined in the normal l e f t ventricle during isometric exercise may, at least in part, be related to the increase i n heart rate; however, factors independent of the frequency of contraction also appear to be operative." Peripheral Heart Trigger Mechanism(s) It has been postulated by Lind et.al. (1964) that: "At least two afferent channels appear to be involved. The f i r s t of these i s responsible for the pronounced cardio-accelerator response and rise of cardiac output, the second results in baroreceptor suppression allowing rapid and very large elevation of the systemic blood pressure. The almost instantaneous return of the heart rate to the control value on releasing the grip is quite remarkable. The similar, almost immediate return of the blood pressure to control values i s equally remarkable particularly as there is a considerable rise of stroke volume in early recovery and the cardiac output remains raised for about five minutes (20 and 50% M.V.C.) afterwards. It appears that the baro-static reflexes return to their f u l l efficiency immediately the grip i s released." 16 Similar peripheral mechanisms have been postulated by Alam and Smirk (1937), Donald et a l . (1967) and Petro et a l . (1970). Hnik et a l . (1969) found that increasing or decreasing the per-fusion pressure and increasing the arte r i a l did not significantly alter the overall discharge frequency of the proprioceptive (la, lb, & II) and non-proprioceptive (III & IV) muscle afferents. However, they did find that intra-arterial infusion of KC1 resulted in either an enhancement of the rate of discharge or the appearance of activity in previously silent endings in both proprioceptive and non-proprioceptive sensory fibers when the K + concentration in the venous blood reached concentrations of 7.5 -12.5 mEq. K + per l i t e r (the range found in venous blood following muscle activity, Kjellmer, 1965). They concluded that muscle afferents may be activated by non-proprioceptive stimuli (K +) arising in the muscle in connection with metabolic changes. Liu et a l . (1969) observed an increased blood pressure, heart rate, and cardiac contractile force following an injection of KC1 (3.5M, 30 mg./kg.) into a femoral artery of morphine-pentobarbital-anesthetized dogs. These responses were: (1) abolished by complete denervation; (2) markedly diminished by the administration of phenoxybenzamine (0.7 mg./kg.) or propanolol (1.0 mg./kg.); and (3) absent following injections of NaCl (3.5M), CaCl 2 (2.5M), MgCl 2 (2.5M), and 50% glucose in 30 mg./kg. amounts in place of KC1; indicating that the response does not occur as a result of changes in osmolality or the prescence of Na , Ca , or Mg . They suggest that receptors sensitive to K are present i n the hindlimb and that the K -evoked nerve impulses are transmitted through the afferent fibers of the somatic nerve to the vasomotor centers of the medulla. They further suggest that the circulatory responses after intra-arterial injection of KC1 are mediated through the release of catecholamines at the sympathetic nerve endings of the heart and blood vessels. Unfortunately, the precise nature of the K -evoked peripheral stimulation i s yet to be documented. Mitchell et a l . (1968) found that stimulation of the central end of a canine quadriceps nerve at a frequency of 100 pulses/sec. with a strength 20 times threshold for the flexion response resulted in an i n i t i a l , brief depressor response followed by a pressor response, that i s , aortic pressure, l e f t ventricular pressure, heart rate and maximal rate of rise of l e f t ventricular pressure a l l increased while l e f t vent-ricular diastolic pressure remained relatively constant. The delay from onset of stimulation to response varied from 2 - 1 5 seconds during the series of experiments. The pressor response was unaltered by a b i l a t e r a l vagotomy or adrenalectomy, but, abolished by the administration of pro-panolol (0.8 mg./kg.). McCloskey and Mitchell (1972), Coote et a l . (1971) and Mitchell et a l . (1968) suggest that small-sized, high-threshold (III & IV) muscle afferents, when stimulated appropriately, may play some role in e l i c i t i n g the increase in l e f t ventricular contractility that occurs during muscular exercise. 18 Freyschuss (1970b) ascribed the heart rate acceleration at the i n i t i a t i o n of handgrip to a reduction in the vagal tone on the heart and concluded, on the basis of his results from "intended exercise" of a succinylcholine-blocked arm, that the rise in heart rate was e l i c i t e d by an autonomic nervous drive of central origin. However, the rise by intended exercise was only half as great as the i n i t i a l heart rate response to actual muscular a c t i v i t y . The results of this study and other studies (Freyschuss, 1970b, tetraplegics and Donald et a l . 1967, syringomyelia) tend to support the hypothesis of an interacting peripheral-cerebral heart trigger mech-anism. This mechanism was suggested by Paulev (1971) when he found that the size of the i n i t i a l heart rate response depends upon the size of the integrated electromyogram (EMG) signal during the f i r s t four seconds of exercise and that two to three kicks on the bicycle ergometer e l i c i t e d a larger i n i t i a l heart rate response than only one kick. Goodwin et a l . (1972) used a vibrator to stimulate the l a afferents i n either the biceps or triceps of their human subjects and cause a tonic vibration reflex, which could reflexly assist or inhibit a voluntary contraction. They demonstrated that this procedure could reduce or increase the amount of central command necessary to maintain a prescribed biceps tension. The prescribed muscular tensions varied between 20 - 50% MVC. They concluded that irradiation of respiratory and cardiovascular control centers by the descending central command does occur during voluntary muscular contraction in man; and that the cardio-pulmonary responses of an isometric effort can be altered by altering 19 the magnitude of the central command. They suggest that both central irradiation and peripheral reflexes are involved in the cardio-pulmonary responses to exercise. Summary The cardioacceleratory response has been estimated to occur between 400 - 600 msec, after the onset of the contraction. The magni-tude of the response has been shown to be related to the %MVC up to 50% MVC, regardless of whether the contraction i s unilateral or b i l a t e r a l , i . e., independent of the muscle mass involved. However, from 50% MVC to 100% MVC no clear relarionship has been found between the magnitude of the response and the %MVC. Studies involving neurologically-handicapped subjects and drug-induced neurological blockades indicate two things: f i r s t l y , an intricate sympathetic-parasympathetic interaction on cardiac response exists; and secondly, the existance of peripheral and central heart trigger mechanisms. It is suspected that the peripheral mechanism i s based on the K concentration and i t s effect on the proprioceptive and non-proprioceptive afferents; while the central mechanism is based on irradiation from the central motor command. It would seem reasonable to assume that these two mechanisms would not act simultaneously. How-ever, no study, to date, has shown or attempted to show the time-course of the cardioacceleratroy response to isometric exercise. 20 CHAPTER III MATERIALS AND METHODS Experimental Design This study was based on a 3 x 3 x 10 factorial design with re-peated measures on the last two factors and 10 subjects nested under each level of the f i r s t factor, that i s , each of the three levels of %MVC con-tained 10 subjects and dependent measures were obtained from each of the 30 subjects for 10 consecutive heart beats i n the resting, contraction and recovery conditions (Fig. 1). Subjects The sample population consisted of 30 alert, non-basal, male volunteers from the population of graduate and undergraduate students at the University of British Columbia, Vancouver, B. C. The age range was from 18 - 28 years with a mean of 22 years. A majority of the subjects were students i n the School of Physical Education and Recreation. Experimental Procedure A l l subjects were tested once, i n random order, during the interval, 3 December, 1974 - 5 December, 1974, i n the Exercise Physiology Laboratory, University of British Columbia, War Memorial Gymnasium. FIGURE 1 EXPERIMENTAL DESIGN Condition Resting Contraction Recovery Subject Heart Beat 1 2 3 4 5 6 7 8 9 10 Heart Beat 1 2 3 4 5 6 7 8 9 10 Heart Beat 1 2 3 4 5 6 7 8 9 10 50% MVC 1 • • 10 75% MVC 11 • • • 20 100% MVC 21 • • 30 3 x 3 x 10 F a c t o r i a l Design with repeated measures on the l a s t two factors and 10 subjects nested under each l e v e l of the f i r s t f a c t o r . 22 Ambient temperature and barometric pressure, during the testing, ranged from 24.0 - 24.5° C. and 744 - 758 torr., respectively. Preparation. Prior to testing, each subject was asked to remove his shirt for placement of the Beckman Biopotential skin electrodes. One of the recording electrodes was attached at the sternal apex and the other was attached at the sixth intercostal-space on the l e f t , lateral portion of the thoracic cage. The ground electrode was attached near the apex of the l e f t scapula. The subject was then asked to l i e comfortably on the testing table in the supine position. The electrodes were connected to a Sanborn ECG preamplifier in conjunction with a 4-channel, paper recorder (Sanborn 500) and adjustments were made un t i l the peak of the ECG R-wave was easily discernible at a recording speed of 100 mm./second. The handgrip dynamometer (model 76618, Lafayette Instrument Co., Lafayette, Indiana) and i t s attached rheostat was connected in series with a dual-trace amplifier (type 3A72, Tetronix, Inc., Portland, Oregon), a Sanborn preamp-l i f i e r , and the 4-channel recorder. Prior to each testing day, the c a l i -bration of the dynamometer paper recording was checked and, i f necessary, adjusted so that a deflection of 1 mm. was equivalent to a 2-kilogram force. 100% MVC Determinations. The method for determining each subject's 100% MVC was essentially the same as the one established by Lind et a l . (1964). The subject was instructed to perform three maximal handgrips, with the right hand, on the dynamometer, using only the arm muscles. The three t r i a l s were recorded on the Sanborn paper recorder and the storage 23 oscilloscope (Tetronix, type 564) by using the lower beam with a time base (Tetronix, type 2B67) of 1-second/division. To ensure between subject consistency, the contractions were performed at 1-minute intervals and the commands "contract" and "release" were given by the experimenter such that the contractions were maintained for approximately 2-seconds. The mean of the two highest values was accepted as the subject's 100% MVC. This was followed by a 5-minute rest period during which both beams of the dual-beam oscilloscope were converted to horizontal lines using a time base of 0.5 msec./division. Using the stored oscilloscope contractions as reference points, the upper beam was positioned to indicate the mus-cular force required of the subject to attain his prescribed %MVC. The contraction force was displayed by the lower beam. The oscilloscope screen was not v i s i b l e to the subject throughout this portion of the procedure. Commands and Instructions. The stored oscilloscope contractions were erased and oscilloscope was released from the storage position. The oscilloscope screen was then positioned so that the subject could easily see the screen by turning his head slightly to the right. He was then given the following commands and instructions: 1. "Inspire" - Upon hearing this command the subject was told that he should take a comfortable inspiration. 2. "Hold" - Upon hearing this command the subject was instructed to block his respiratory movements without forcefully contracting his ab-dominal muscles, u n t i l he was given the "release" command. This prevented the occurrence of a Valsalva Maneuver. 24 3. "Contract" - Upon hearing this command the subject was told to perform a contraction as quickly as possible so that the lower o s c i l l o -scope line would match the upper oscilloscope line and to maintain this match u n t i l he was given the "release" command. Then the experimenter demonstrated the required response to prevent the subject from obtaining information concerning his prescribed %MVC. 4. "Release" - Upon hearing this command the subject was instructed to release the dynamometer immediately, resume normal breathing, and l i e quietly on the testing table. The preceding procedure was developed from previous studies, that have demonstrated the effects of respiration (Davies and Nielson, 1967), breath-holding (Petro et a l . , 1970), and the Valsalva Maneuver (Flessas et a l . , 1970) on heart rate. Furthermore, Borst et a l . (1972) and Petro et a l . (1970) found that their subjects naturally blocked their respir-ation during isometric contractions; and Paulev (1971) found the change in ventilation, either a rise or reduction, occurs instantly at the start and end of exercise before the heart rate response. Data Recording. At the end of the 5-minute rest period, muscle tension and ECG's were simultaneously recorded at a paper speed of 100 mm./sec. for a l l three conditions. The resting (actually pre-contraction), contraction and recovery values were recorded continuously for 40-seconds. The commands "inspire" and "hold" were given 4- and 3-seconds, respectively, prior to the "contract" command, which was followed by the "release" 25 command after a 10-second period. Recovery values were recorded for the last 15-seconds. Cycle time (msec.) was chosen as the dependent measure of cardiac response i n preference to heart rate (beats/min.) for three main reasons: (1) i t i s predominantly the shortening of diastole that indicates the occurence of cardioacceleration; "(2) expressing the cycle time of a single heart beat in beats per minute requires j u s t i f i c a t i o n ; and (3) due to the non-linearity of the relationship between cycle time and heart rate (as demonstrated by Table I and Fig. 2) a transformation would alter the mag-nitude of any comparative changes. This choice i s supported by the study of Jennings et a l . (1974), which indicated that the cycle time distribution of 10 males between 16- and 25-years old was not significantly different from a normal distribution, whereas, the heart rate distribution was sig-nificantly different. Khachaturian and Kerr (1972) reported that s i g n i f i -cant differences in variance are introduced by transforming cycle time data.into heart rate. They suggested that this problem becomes particu-l a r l y important when the study in question involves averaging ECG re-sponses across t r i a l s or states. S t a t i s t i c a l Analyses The raw scores, cycle length (mm.) and muscular tension (mm.), for each subject under each of the three conditions were obtained from the 2-channel Sanborn recording paper as defined in Chapter I. Cycle time (msec.) and muscular tension (kg.) were calculated according to the follow 26 TABLE I Relationship between cycle time (R-R interval) and the corresponding heart rates. Cycle Time (msec.) 1400 Heart Rate (bpm) 42.9 Heart Rate Change 1.5 1350 44.4 1.8 1300 46.2 1.8 1250 48.0 2.0 1200 50.0 2.2 1150 52.2 2.3 1100 54.5 2.6 1050 57.1 2.9 1000 60.0 3.2 950 63.2 3.4 900 66.7 3.9 850 70.6 4.4 800 75.0 5.0 750 80.0 5.7 700 85.7 6.6 650 92.3 7.7 600 100.0 9.1 550 109.1 10.9 500 120.0 13.3 450 133.3 16.7 400 150.0 FIGURE 2 Cycle Time (milliseconds) M 28 ing formulas: 1. Cycle Time (msec.) = Cycle Length (mm.) x 10 (recording paper speed = 100 mm./sec.) 2. Muscular Tension (kg.) = Muscular Tension (mm.) x 2 (calibration: 1 mm. = 2 kg.) and recorded on computer coding sheets prior to being key-punched onto computer data cards. In addition each subject's maximal voluntary con-traction was obtained from the recording paper and determined as outlined previously. Then expressed i n kilograms according to formula (2.) and recorded on the computer coding sheets. The experimental design (Fig. 1) was not an appropriate design for the s t a t i s t i c a l analysis of the experimental data, because, the levels of the f i r s t factor could not be crossed with a l l levels of the last two factors and s t i l l be meaningful. Therefore, the experimental data obtained under each condition were analyzed according to the s t a t i s t i c a l design illustrated by Figure 3. A l l two-way analyses of variance (ANOVA) and trend analyses were performed on the University of British Columbia's IBM 360/67 computer using the "canned" program, "Repeated Measures Analysis of Variance (UBC BMDP2V)," (Sampson, 1974), and a l l post-hoc Newman-Keuls analyses were performed as outlined by Winer (1971). 29 FIGURE 3 STATISTICAL DESIGN Condition (Resting, Contraction, or Recovery) Heart Beat Subject 1 2 3 4 5 6 7 8 9 10 1 2 3 4 50% MVC 5 6 7 8 9 10 11 12 13 14 75% MVC 15 16 17 18 19 20 21 22 23 24 100% MVC 25 26 27 28 29 30 o •r) •W O rt •p c o o f>N M rt 4-1 9 o > rt S •H 3 cu 3 x 10 Factorial Design with repeated measures on the second factor and 10 subjects nested under the f i r s t factor. 30 Resting Condition. A two-way ANOVA and trend analysis was per-formed on the dependent variable (CT) to test the effectiveness of the random assignment. Followed by a post-hoc Newman-Keuls analysis to deter-mine the effect of the inspiration resulting from the "inspire" and "hold" commands. The post-hoc Newman-Keuls analysis indicated that each subject's CT just prior to contraction (resting heart beat 10) would be appropriate to use as his CT . A Fortran program was written and developed to compute each subject's MT_, ACCT . RCCT , ACCT , and RCCT ; and appropriately punch R C C R K each subject's dependent variables for the contraction and recovery condi-tion onto data cards in preparation for s t a t i s t i c a l analyses. Contraction Condition. Four two-way ANOVA's and trend analyses were performed on the four dependent variables (CT , ACCT , RCCT , and MTD) C C* C R to test hypotheses 1 and 2. Followed by a post-hoc Newman-Keuls analysis of MT , within each level of %MVC, to test the valid i t y of the assumption R underlying hypothesis 1. This was followed by a post-hoc Newman-Keuls analysis of RCCT , within each level of %MVC, to indicate the beats at which the changes i n trend were occurring. Then, three two-way ANOVA's were performed on RCCT^ in order to make the following comparisons: 1. 50% MVC Vs. 75% MVC 2. 50% MVC Vs. 100% MVC 3. 75% MVC Vs. 100% MVC to further test hypothesis 1. These comparisons should normally be made with a post-hoc procedure. However, on the advice of a sta t i s t i c i a n , preceding procedure was considered to be more meaningful. Recovery Condition. A two-way ANOVA and trend analysis was formed on RCCT to test hypothesis 3. K 3 2 CHAPTER IV RESULTS AND DISCUSSION Results Each subject's age, three maximal voluntary contractions scores, and determined 100% MVC are presented i n Table I of Appendix A. The level of confidence for a l l s t a t i s t i c a l tests was set at 0.05 unless otherwise specified. Resting Descriptive S t a t i s t i c s . Individual cycle times for a l l subjects and a l l 10 beats (heart beats) are presented i n Table II of Appendix A. Means and standard deviations were calculated from these scores for each of the 10 beats of each group (%MVC) and are presented in Table II with a graphic plot of the pooled means displayed i n Figure 4. S t a t i s t i c a l Analyses. The ANOVA (Table III) indicated a non-significant groups effect and interaction (%MVC x Beats), but a s i g n i f i -cant beats effect was found. The post-hoc Newman-Keuls analysis (Table IV) showed that the mean pooled CT's of beats 7, 8 and 9 were significantly different than TABLE I I Resting Condition - Means and Standard Deviations of Cycle Time (CT) Expressed in Milliseconds for all Groups and all 10 Heart Beats. Heart Beat Group 1 2 3 4 5 6 7 8 9 10 50$ MVC 936.0 945.5 908.5 925.0 975.5 947.5 855.0 820.5 829.0 881.0 ±186.1 ±193.5 ±153.4 ±199.9 ±247.3 ±232.7 ±173.7 -±142.1 ±107.5 ±101.7 75£ MVC 923.0 922.0 901.5 932.0 948.5 893.0 847.5 809.5 858.0 954.0 ±168.4 ±152.1 ±135.3 ±134.4 ±167.0 ±159.1 ±142.6 ±68.2 ±82.3 ±169.8 10C# MVC 876.0 890.5 893.5 863.5 863.5 836.5 788.0 768.5 777.5 870.0 ±161.0 ±164.2 ±165.5 ±134.4 ±149.2 ; ±160.8 ±171.0 ±152.7 ±129.3 ±136.3 Pooled 911.7 919.3 901.2 . 906.8 929.2 892.3 830.2 799.5 821.5 901.7 LO FIGURE 4 Heart Beat The e f f e c t of i n s p i r a t i o n on Resting Cycle Time. The arrow approximates the point at which the subjects were t o l d to comfortably i n s p i r e and block t h e i r breathing i n preparation f o r the contraction. TABLE III Summary of ANOVA Resting - Cycle Time (CT) Source df MS F P Between Subjects 29 2 111942.0 0 . 6 0 NS Ss w. $MVC 27 c 188123.3 Within Subjects 270 Beats 9 63748.8 S .84 < . 0 1 B e a f c 3 ( l i n . ) 1 218405.5 9.97 < . 0 1 B e a t s ( q u a d . ) 1 6112.4 0.42 NS B e a t 3 ( c u b i c ) 1 187691.6 23 .34 < . 0 1 %MVC x Beats 18 4868.6 0.68 NS Beats x Ss w. %WC 243 7210.4 Beats x Ss w. $MVC( l i n N 27 21906.9 Beats x S3 w. %^cfquad ) 27 14429.7 Beats x Ss w. #MVC c u b i c\ 27 8042.5 * NS denotes that the F-ratio i s not s i g n i f i c a n t at the 0.05 l e v e l of confidence. T A B L E I V 36 Newman-Keuls Analyses of Paired Comparisons Resting - Cycle Time (CT) S5 = 15.503 r = 2 3 4 * Sgq>95(r,243) = 2.77 3.31 3.63 5 6 7 8 9 10 3.86 4.03 4.17 4.29 4.39 4.47 Ordered Means 799.5 821.5 830.2 892.3 901.2 901.7 906.8 .911.7 919.3 929.2 Beats 8 9 7 6 8 - - * 3 10 4 1 2 -* * # # # 5 -K-9 - * * *-7 . * •M- * •* # . 6 - - . - . - - — * Denotes that the paired means are level of confidence. - Denotes that the paired means are significantly different at the 0.05 not significantly different at the 0.05 level of confidence. 37 the mean pooled CT's of the remaining beats, which were not significantly different from each other. On the basis of these results, the f i r s t beat prior to contraction was used in determining each subject's control cycle time. Contraction Descriptive Statistics. Individual raw scores (CT C and MT) and individual computed scores (ACCT , RCCT , and MT ) for a l l subjects C C R and a l l 10 beats are presented in Tables III and IV of Appendix A, and Tables I, II and III of Appendix B, respectively. From the appropriate preceding results, means and standard deviations of MTR, RCCT^ ,, CT^ , and ACCT^ , were calculated for each of the 10 beats of each group and are presented i n Tables V, VIII, XI and XIII, respectively, with a graphic plot of the means displayed in Figures 5, 6, 7 and 8, respectively. S t a t i s t i c a l Analyses. The MTR ANOVA (Table VI) indicated a significant beats effect, groups effect and interaction. The trend analysis indicated that there was a significant linear, quadratic, and cubic trend through beats with a significant difference in these trends between groups. Post-hoc Newman-Keuls analyses was performed on the means of the 10 beats for the 100% MVC group (Table VII A), 75% MVC group (Table VII B) and 50% MVC group (Table VII C). The analyses indicated that the 38 mean MT 's were not significantly different after the fourth beat for K the 100% MVC group and after the third beat for the 75% and 50% MVC groups. The ANOVA's and trend analyses of CT C > ACCTC> and RCCTC are summarized in Tables XII, XIV and IX, respectively. They show that the F-ratios obtained using CT_ or ACCT were consistently smaller than those obtained using RCCT , except for the main effect of groups and the quad-ratic trend in beats. The trend analysis of RCCT indicated that the linear and quad-ratic trends i n beats were different between the three groups. More powerful trend analyses (the level of confidence was set to 0.01) were performed by making the following paired comparisons: 1. 50% MVC Vs. 75% MVC (Table I of Appendix C) - indicated a significant linear trend in beats with no difference in linear trend between the two groups. 2. 50% MVC Vs. 100% MVC (Table II of Appendix C) - indicated a significant linear and quadratic trend in beats with a significant diff= erence in the two trends between the two groups. 3. 75% MVC Vs. 100% MVC (Table III of Appendix C) - indicated a significant linear and quadratic trend in beats with a significant d i f f -erence in the two trends between the two groups. 39 The post-hoc Newman-Keuls analyses on the means of the 10 beats for the three groups indicated the following (in terms of RCCT ): 1. 100% MVC (Table X A) - indicated significant differences between each of the f i r s t five beats with a change in the trend during the following five beats. 2. 75% MVC (Table X B) - indicated that the only significant difference i n the f i r s t five beats was between the f i r s t and the remain-ing four. However, the last five beats showed a similar trend to that of the 100% MVC group. 3. 50% MVC (Table X C) - indicated that the only significant difference was between the f i r s t beat and the remaining nine beats. Recovery Descriptive Statistics. The individual raw scores and individual computed scores (ACCT and RCCT ) for a l l subjects and a l l 10 beats are R R presented in Table IV of Appendix A and Tables IV and V of Appendix B, respectively. From these results, the means and standard deviations of RCCT , CT and ACCT were calculated for each of the 10 beats of each R R R group and are presented in Table XV, and Tables I and II of Appendix D, respectively, with a graphic plot of the means displayed i n Figure 9, and Figures 1 and 2 of Appendix D, respectively. S t a t i s t i c a l Analysis. The trend analysis (Table XVI) indicated a significant linear trend in beats with a significant difference in this trend between groups. TABLE V Contraction Condition - Means and Standard Deviations of Relative Muscular Tension (MTR) Expressed in Per Cent for all Groups and all 10 Heart Beats. Group 1 2 3 4 5 6 7 8 9 10 5C# MVC 0.00 ±0.00 J35.03 ±13.96 47.07 ± 3 . 2 7 48.58 ±3.11 48.57 ±3.18 48.19 ±3.16 48.12 ±3.14 48.41 ±3.81 48.41 ±3.81 48.20 ±3.63 75$ MVC 0.00 ±0.00 ,60.42 ±11.60 74.69 ±3.48 74.66 13.39 74.30 ±2.37 74.32 ±2.32 74.06 ±2.29 73.73 ±2.10 74.07 ±2.11 74.26 ±2.37 !0C$ MVC 0.00 ±0,00 J2.49 ±20.65 85.71 ±12.66 94.51 ±5.41 96.05 ±3.16 96.46 ±3.17 96.49 ±3.55 96.43 ±3.62 96.99 ±4.05 96.70 ± 3 . 9 9 FIGURE 5 Heart Beat >-> Contraction Condition - ' ' Relative Muscular Tension during the first 10 Heart Beats. TABLE VI 42 Summary of ANOVA Contraction - Relative Muscular Tension (MTR) Source df MS F P Betweem Subjects 29 2 38757.7 367.54 < .01 Ss w. #MVC 27 105.5 • Within Subjects 270 Beats 9 16280.8 514.60 < .01 B e a t s ( l i n . ) 1 64720.1 815.80 < .01 B e a t s(quad.) 1 52154.3 4957.38 < .01 B e a t s ( c u b i c ) 1 23552.6 787.57 < .01 %WJC x Beats 18 790.4 24.98 < .01 %WG x BeatS£ l i n j 2 3982.6 50.20 < .01 2MVC x B e a t s ( q u a d L ) 2 2057.2 195.54 < .01 %MC x B e a t s ( c u b i c ) 2 540.2 18.06 < .01 Beats x Ss w. %W0 243 31.6 Beats x Ss w. #MVC(liru) 27 79.3 Beats x Ss w. %^^{qQa<l.) 27 10.5 Beats x Ss w. %^(^CVihxc) 27 29.9 * NS denotes that the F-ratio is not significant at the 0.05 level of confidence. TABLE VII 43 Newman-Keuls Analyses of Paired Comparisons Contraction - Relative Muscular Tension (MTR) S g = 1.026? r = 2 3 4 5 6 7 8 9 10 ¥ . 9 5 ( r ,243) = 2.77 3.31 3.63 3.86 4.03 4.17 4.29 4.39 4.47 - TABLE VII(A) 10C# MVC Ordered Means 0.00 52.49 85.71 94.51 96.05 96.43 96.46 96.49 96.70 96.99 Beats 1 2 3 4 5 8 6 7 10 9 1 * -X- * * 2 -A- -X X X # 3 # . # •»• •»• # * Denotes that the paired means are level of confidence. - Denotes that the paired means are 0.05 level of confidence. significantly different at the 0.05 not significantly different at the TABLE VII(B) 44 75% MVC Ordered Means 0.00 60.42 73.73 74.06 74.07 74.26 74.30 74.32 74.66 74.69 Beats 1 2 8 7 9 10 5 6 4 3 1 X tt tt tt tt * # 2 tt * « * •* 8 TABLE VII(C) 5C# MVC Ordered Means 0.00 35.03 47.07 48.12 48.19 48.20 48.41 48.41 48.57 48.58 Beats 1 2 3 7 1 tt * tt 2 tt # 3 6 10 8 9 5 4 * * # * * * * * tt tt tt tt * Denotes that the paired means are s i g n i f i c a n t l y d i f f e r e n t at the 0.05 l e v e l of confidence. - Denotes that the paired means are not s i g n i f i c a n t l y d i f f e r e n t at the 0.05 l e v e l of confidence. TABLE VIII Contraction Condition - Means and Standard Deviations of Relative Change in Cycle Time (RCCTC) Expressed in Per Cent for all Groups and all 10 Heart Beats. Group 1 2 3 4 Heart Beat 5 6 7 8 9 10 50% MVC -4.83 113.41 . 0.50 112.02 . 1.95 112.75 , 1.05 115.77 . 0.39 ±18.04 . 1.35 ±18.46 . 2.09 119.09 , 2.42 •±19.08 4. 3.17 ±17.72 ±16.82 15% MVC 2.46 16.22 7.69 17.43 6.64 19.52 ,7.53 19.86 8.91 18.65 12.38 19.78 14.26 ±10.96 14.88 ±12.32 16.18 ±12.50 15.54 ±12.77 100% MVC r0.51 17.10 . 7.95 110.35 .14.04 111.22 .19.68 l l 2 . 8 3 22.63 l l 3 . 0 1 ,23.75 113.31 .24.99 ±13.28 ,26.61 -12.55 27.62 ±12.51 ,27.54 ±12.35 4> FIGURE 6 Contraction Condition - Relative Change in Cycle Time during the first 10 Heart Beats. Arrows indicate the heart beat at which each group attained it's prescribed level of $MVC, TABLE IX 47 Summary of ANOVA Contraction - Relative Change i n Cycle Time (RCCTP) Source df MS F P Between Subjects 29 %WC 2 8402.9 5.42 < .01 Ss w. %WJC 27 1549.1 Within Subjects 270 Beats 9 830.8 40.03 < .01 B e a t s ( l i r u ) 1 6579.8 61.09 < .01 B e a t 3 ( q u a d . ) 1 713.3 21.14 < .01 B e a f c s ( c u b i c ) 1 63.5 2.80 NS %WC x Beats 18 164.1 7.91 < .01 %WJC x Beatsp i r, f y 2 1082.6 10.05 <.01 %mC x B e a t s ( q u a d u ) 2 286.6 8.50 <.01 *HVC x B e a t s ( c u b i c ) 2 52.8 2.32 NS Beats x Ss w. #MVC 243 20.8 Beats x Ss w. % M V C ( 1 i n j 27 107.7 Beats x Ss w. #MVC( q u a d #) 27 33.7 Beat3 x Ss w. #MVC( c u b i c) 27 22.7 * NS denotes that the F-ra t i o i s not s i g n i f i c a n t at the 0.05 l e v e l of confidence. TABLE X 48 Newman-Keuls Analyses of Paired Comparisons Contraction - Relative Change i n Cycle Time (RCCTQ) Sg = 0.8317 r 2 3 4 5 6 7 8 9 10 S g q e 9 5 ( r , 2 4 3 ) = 2.77 3.31 3.63 3.86 4.03 4.17 4-29 4.39 4.47 TABLE X ( A ) 100$ MVC Ordered Means -0.51 7.95 14.04 19-68 22.63 23.75 24.99 26.61 27.54 27.61 Beats 1 2 3 4 5 6 7 8 10 9 1 * # tt * tt tt 2 tt * * * 3 * * * •»• tt tt 4 * tt tt 5 - - tt tt tt 6 tt tt * Denotes that the paired means are s i g n i f i c a n t l y d i f f e r e n t at the 0.05 l e v e l of confidence. - Denotes that the paired means are not s i g n i f i c a n t l y d i f f e r e n t at the 0.05 l e v e l of confidence. TABLE X(B) 15% MVC Ordered Means 2.46 6.64 7.53 7.69 8.91 12.38 14.26 14.88 15.54 16.18 Beats 1 3 4 2 5 6 7 8 10 9 1 * * tt # * 3 - _ ' * . # . # > 4 _ _ # • * . » * * 2 _ . • » • • » • • » # # 5 * #~ • 6 _ _ tt * 7 -TABLE X(C) 50$ MVC Ordered Means - 4 . 8 3 0.39 0 . 5 0 1.05 1.35 1.95 2.09 2.42 2.93 3 .17 Beats 1 5 2 4 6 3 7 8 10 9 1 # * tt tt tt tt 5 * Denotes that the paired means are significantly different at the 0.05 level of confidence. - Denotes that the paired means are not significantly different at the 0.05 level of confidence. TABLE X I Contraction Condition - Means and Standard Deviations of Cycle Time (CTQ) Expressed in Milliseconds for all Groups and all 10 Heart Beats. Group 1 2 3 4 Heart Beat 5 6 7 8 9 10 50$ MVC 925.0 ±1 7 6 . 1 873.0 ±115.4 859.0 ±107.8 866.5 ±128.2 873.5 ±154.3 865.0 ±157.2 857.0 ±152.1 853.5 ±147.7 846.0 ±131.7 848.5 ±127.9 15% MVC 926.0 ±142.3 873.5 ±119.1 882.0 ±119.8 872.5 ±111.3 860.0 ±106.8 824.5 ± 8 6 . 7 804.5 ±73.5 796.5 ±64.3 784.5 ±70.9 792.0 ±91.5 100$ MVC 870.5 ± 1 2 3 . 7 793.5 ±110.7 739.5 ±104.4 689.5 ±109.3 663.5 ±107.9 654.5 ± 1 1 5 . 7 644.0 ±116.2 630.0 ±1 0 9 . 4 621.0 ±107.0 623.0 ±115.4 O FIGURE 7 H950-T T T 1 i i t s -90& 850 ra C o o CO OJ • H •a ID 0) rH O r800 T" - i - f I 1 J_L l I i i L L 25$. r m n T T T 750 M44-s I i I >» .-r o T T Si I I I l-i-L 1 M ! I rnxnn: 650 600 I ' M l I 4 I ! 1 T T ? t t i - L i -t± 4100$ MVG ! ! I I 1 1 I ^ T + T T f r t f r ^ 4-2- 4 i 5 Heart Beat Contraction Condition - Cycle Time during the f i r s t 10 Heart Beat3. Arrows indicate the heart beat at which each group attained i t * s prescribed l e v e l of $MVC. TABLE XII 52 Summary of ANOVA Contraction - Cycle Time (CT C) Source df MS F P Between Subjects 29 $MVC 2 882446.5 7.08 < .01 Ss w. $MVC 27 124648.7 Within Subjects 270 Beats 9 73109.7 36.34 < .01 B e a t s ( l i n . ) 1 578218.5 52.97 < .01 B e a t 3 ( q u a d . ) 1 61966.5 22.15 < .01 B e a t s ( c u b i c ) 1 5406.6 2.42 NS %WJC x Beats 18 12140.1 6.03 < .01 %WJC x B e a t s ( l i n # j 2 76913.2 7.05 < .01 $MVC x B e a t s ( q u a d > ) 2 22334.9 7.98 < .01 %WJC x B e a t s ( c u b i c ) 2 5027.4 2.25 NS Beat3 x Ss w. $MVC 243 2011.8 Beats x Ss w. %^(^jL±n^) 27 10916.1 Beats x S 3 w. $MVC(q u a c^) 27 2797.5 Beats x Ss w. $MVC( c u b i c) 27 2235.9 * NS denotes that the F-ra t i o i s not s i g n i f i c a n t at the 0.05 l e v e l of confidence. TABLE XIII Contraction Condition - Mean3 and Standard Deviations of Actual Change i n Cycle Time (ACCTC) Expressed in Milliseconds for a l l Groups and a l l 10 Heart Beats. Heart Beat 10 Group 1 2 3 4 5 6 7 8 9 50$ MVC -44.0 ±126.7 8.0 ±98.1 22.0 ±104.1 ^ 14.5 ±127.1 ±144.0 16.0 ±147.2 24.0 ±152.3 ^ 27.5 ±152.0 ^ 35.0 ±143.2 ±137.5 15% MVC 28.0 ±63.3 80.5 ±83.6 72.0 ±103.4 81.5 ±109.3 %.o ±99.6 129.5 ±118.2 149.5 ±129.9 157.5 ±146.5 ,169.5 1148.7 162.0 ±148.0 100$ MVC -0.5 ±65.9 • 76.5 ±101.0 130.5 ±112.8 180.5 ±133.1 206.5 ±136.4 215.5 ±139.7 226.0 ±140.3 240.0 ±135.5 249.0 ±136.4 247.0 ±132.8 FIGURE 8 81 T » C o o 0) 0) E-" o >» o © tiO c CO. Si o CO o Heart Beat Contraction Condition - Actual Change in Cycle Time during the first 10 Heart B e a t 3 . Arrows indicate the heart beat at which each group attained it's prescribed level of $MVC. TABLE XIV 55. Summary of ANOVA Contraction - Actual Change in Cycle Time (ACCTQ) Source df MS F P Between Subjects 29 $MVC 2 671885.5 4.76 < .02 Ss w. %WC 27 14L221.4 Within Subjects 270 Beats 9 73110.3 36.34 < .01 B e a t 3 ( l i n . ) 1 578224.5 52.97 < .01 B e a t 3(quad.) 1 61967.A 22.15 < .01 B e a t s ( c u b i c ) 1 5406.5 2.42 NS %WJC x Beats 18 12140.I 6.03 < .01 $MVC x Beats( l i n >) 2 76913.6 7.05 < .01 %WJC x B e a t s ( q u a d 0 2 22334.9 7.98 < .01 %WIC x Beats( c u b i c) 2 5027.4 2.25 NS Beats x Ss w. $MVC 243 2011.8 Beats x Ss w. £MVC( l i r u) 27 10916.1 Beats x Ss w. $MVC(quad>) 27 2797.5 Beats x Ss w. $MVC( c u b i c) 27 2235.9 * NS denotes that the F-ratio is not significant at the 0.05 level of confidence. TABLE XV Recovery Condition - Means and Standard Deviations of Relative Change in Cycle Time (RCCTR) Expressed in Per Cent for all Groups and all 10 Heart Beats. Heart Beat Group 1 2 3 4 5 6 7 8 9 50$ MVC 2.24 ±15.30 -1.60 ±14.18 -9.18 ±17.16 -6.45 ±15.00 75$ MVC 12.73 ±18.26 • 5.83 ±18.40 ^ 4.02 ±15.64 ±17.08 100$ MVC 26.93 ±17.37 22.25 ±24.00 17.33 ±24.67 10.37 ±21.93 -7.21 ±14.46 -6.72 ±13.55 -7.30 ±13.74 -5.93 ±15.08 -10.69 ±15.01 -10.82 ±17.17 9.06 ±16.18 ^ 8 . 6 4 ± 1 5 . 0 7 ^ 7.27 ±14.83 A 7.52 ±12.28 ^ 6.89 ±13.64 ^ 7.41 ±13.46 10.32 ±20.63 8.06 ±21.06 ^ 2.59 ±19.65 -11.16 ±46.72 -4.53 ±24.02 -3.68 ±21.42 FIGURE 9 TABLE XVI 58 Summary of ANOVA Recovery - Relative Change i n Cycle Time (RCCTR) Source df MS F P Between Subjects 29 2 6566.8 2.63 NS ss w. %mc 27 2495.4 Within Subjects 270 Beats 9 872.5 6.41 < .01 B e a t 3 ( l i n . ) 1 6730.8 16.45 < .01 B e a t 3 ( q u a d . ) 1 351.9 1.97 NS B e a t 3 ( c u b i c ) 1 126.2 0.97 NS %MC x Beats 18 422.0 3.10 < .01 %WIC x B e a t s ^ ^ j 2 3096.5 7.57 < .01 .%MC x B e a t s ( q u a c U ) 2 18.7 0.10 NS $MVC x B e a t s ( c u b i c ) 2 262.6 2.01 NS Beats x Ss w. %WC 243 136.0 Beats x Ss w. $MVC( l i n o) 27 409.3 Beats x Ss w. $MVC( q u a d j 2? 178.4 Beats x Ss w. $ M V C ( c u b i c ) 27 130.5 * NS denotes that the F- r a t i o i s not s i g n i f i c a n t at the 0.05 l e v e l of confidence. 59 Discussion Resting The ANOVA on resting cycle time (Table III) shows a non-signifi-cant groups effect indicating that the random assignment of subjects to groups was effective. The "inspire" command was given just prior to beat six and the significant difference of beats 7, 8 and 9 from the remaining beats indicated that maximum tachycardia occurred at beat 8. This finding supports those of Davies and Neilson (1967), who found that a fast inspiration in the supine position produced maximum tachycardia in 3-seconds and maximum bradycardia in 4.8-seconds. This may pa r t i a l l y explain the negative mean values of RCCT^ for beat one. Unfortunately, respiration was not measured during this condition. As a result, the interacting effects of inspiration and contraction were d i f f i c u l t to explain. Beat ten was ut i l i z e d as the control cycle time and selected on the basis of the N-K analysis along with the fact that i t had been ut i l i z e d as the control value in previous studies (Borst et a l . , 1972, and Petro et a l . , 1970) and should be representative of autonomic tone just prior to contraction. This choice may have been inappropriate, as demonstrated by some of the individual resting cycle times, especially 60 in the case of subject 1. In addition, testing was done just prior to term examinations, and most subjects were unfamiliar with the testing equipment and procedure, which may have caused anxiety. However, sel-ection of control cycle times on an individual basis was unjustifiable. Contraction The mean MT 's of each beat for each group (Table V) indicated R that the relative muscular tension attained by each group was consis^-tently lower than the prescribed muscular tension (i.e., 50%, 75% and 100%). This consistent undershooting can be attributed to the inexact calibration of the oscilloscope screen. For ease of discussion the attained muscular tension w i l l be considered equivalent to the prescribed value. The results indicated that the response time assumption under-lying hypothesis 1 was not violated. Although, the N-K analyses on MT indicated attainment of the prescribed %MVC by beat 4, 3 and 3, for the 100%, 75% and 50% MVC groups, respectively; the time of attainment (deter-mined by summing cycle times) 3.1 s e c , 2.7 s e c and 2.7 s e c , respec-tively, was essentially the same in terms of the assumption. Test of Hypothesis 1. The significant linear trend (p<.01) and the significant groups by linear trend interaction (p<.01) supported hypothesis 1. The trend analyses of paired comparisons showed that the 61 the linear trend for the 100% MVC group was significantly different from the linear trends for the 75% MVC group (p<.01) and the 50% MVC group (p<.01). However, the linear trend for the 75% MVC group was not sig-nificantly different from the linear trend for the 50% MVC group, due to the v i r t u a l abscence of a linear trend for the 50% MVC group ( as indicated by Figure 6). The N-K analyses for RCCT in the 100%, 75% and 50% MVC groups indicated the following: (1) The f i r s t five beats of the 100% MVC group were s i g n i f i -cantly different from each other i n successive order. (2) Only beat 1 was significantly different from beats 2, 3, 4 and 5 i n the 75% and 50% MVC groups. (3) The 100% and 75% MVC groups showed similar trends for beats 6 to 10, as indicated by the N-K analyses. The 50% MVC group showed a similar trend over tha last five beats, as can be seen in Figure 6, but, the trend was not supported in terms of the N-K analyses as i t was for the 100% and 75% MVC groups. (4) A l l three groups showed an reversal of beats 9 and 10, in terms of ordered means, suggesting a possible over-compensation of the heart-trigger mechanism(s). The difference in responses for the f i r s t five heart beats the last five heart beats for the three groups suggests that there 62 were at least two different heart-trigger mechanisms involved. The f i r s t mechanism was almost instantaneous and may have been the central heart-trigger mechanism that has been proposed to operate on central irradiation, whereas,the second mechanism was slower acting (in that i t did not appear to show any apparent effects u n t i l the sixth heart beat) and may have been the peripheral heart-trigger mechanism oper-+ ating on the basis of the K concentration and i t s effect on the pro-prioceptive and non-proprioceptive afferents. Previous studies (Humphreys and Lind, 1963, and Freyschuss, 1970b) reported d i f f i c u l t y in detecting a relationship between the change in heart rate i n the range 50% MVC - 100% MVC. Since then, Jennings et a l . (1974) and Khachaturian and Kerr (1972) have advocated the use of cycle time in preference to heart rate in the analysis of evoked cardiac responses; and this study supports their suggestion. N-K analyses indicated, in terms of the f i r s t five beats for the 50% and 75% MVC groups, no significant -change i n RCCTr after the second beat; whereas, the prescribed muscular tension was not attained u n t i l the third beat with a significant difference in tension between the second and third beat. This showed that at the onset of the con-traction the cardioacceleration did not appear to be influenced by a peripheral" heart-trigger mechanism which was dependent on the relative muscular tension, but may have been the result of a cerebral irradiation i n i t i a t i n g vagal tone withdrawal. This suggestion of vagal tone with-drawal was based on the studies by Levy and Zieske (1969) on sympathetic-63 parasympathetic interaction, and Toda and Shimamoto (1968) on sympathetic stimulation response time. Hnik et a l . (1969) found a latency of 60 sec. or more from the time of infusion of K + to the onset of increased discharge frequency of the sensory fibers. They suggested this latency was a result of the time required for the to diffuse into the v i c i n i t y of the sensory nerve endings and attain a sufficient local concentration to enhance the activity of these endings. However, during a normal contraction i t would be reasonable to assume that the latency would be much shorter because the diffusion distance would be negligible and the rate of increase in local K concentration would depend mainly on the relative number of muscle fibers involved and the local blood flow rate. Liu et a l . (1969), Mitchell et a l . (1968) and, Toda and Shimamoto (1968) demonstrated that K -sensitive, group III and/or IV sensory afferents could e l i c i t a predominantly "sympathetic" cardiovas-cular response, similar to that observed in man. Furthermore, this response was not apparent unt i l after a delay of at least 2-seconds. Humphreys and Lind (1963) reported that the blood flowed through the forearm during a handgrip contraction u n t i l the tension exceeded 70% MVC; and Staunton et a l . (1964) found that complete occlusion of the active muscles potentiated the pressor reflex. These findings, in light of the preceding findings and postulations, suggest 64 that a similar peripheral heart trigger mechanism is operating during isometric contractions in man. Furthermore, the greater the tension, especially above 70% MVC, the more rapid the onset of the cardiovascular response with a minimal latency of 2-seconds. This proposed mechanism could assist in muscular homeostasis by increasing perfusion pressure + to increase blood flow, resulting in a decrease in K concentration which would result in a decreased sensory afferent activity. In terms of the present study, i t i s proposed that the postu-lated mechanism had exerted a s t a t i s t i c a l l y detectable influence by beat five for the 75% MVC group and somewhat earlier for the 100% MVC group, in fact, at such a time that there was a merging of cerebral-peripheral influences. Test of Hypothesis 2. The trend analyses F-ratios for MT^ and RCCT were consistently larger than those of either CT or ACCT , \J W LA* with the exception of the RCCT F-ratio for the quadratic trend of beats. These results indicated that the use of RCCT^ , as the dependent measure generally resulted in a relatively smaller unexplained (error) variance, thereby, supporting the hypothesis. Recovery Test of Hypothesis 3. The trend analysis indicated a signif-icant difference in the linear trend between group?;, which supported 65 the hypothesis. However, as indicated by Figure 9, the significant linear trend and resulting significant difference between groups was predominantly a result of the pronounced linear trend in the 100% MVC group with a slight linear trend in the 50% MVC group and v i r t u a l l y no linear trend in the 75% MVC group; and indicated non-support for the hypothesis. Davies and Nielson (1967) reported that forced expiration from a breath-held position invariably produced a slight f a l l in heart rate followed by a rise. Although, respiration was not recorded in this study this response probably occurred and masked the trends resulting from the relaese of the contraction. This may explain the plateau or rebound tendency observed in Figure 9. Paulev (1971) found, following a 100% MVC handgrip held for 60-sec, a reduction in heart rate after a delay and a relative increase in the depth of the f i r s t two respirations. This study, in contrast, showed no apparent delay before the reduction occurred. 66 CHAPTER V SUMMARY AND CONCLUSIONS Summary The purpose of this study was to examine the effects of iso-metric contractions on the heart and determine the time-course of the change of the cardioacceleratory response. Further, the study examined the degree of relatedness of muscular tension to cycle time, relative change in cycle time and actual change in cycle time. In addition, the study examined the time-course of the recovery of the cardiac response to the isometric contraction. A total of 30 males between the ages of 18 - 28 years were involved in the experiment as subjects. Each subject was randomly assigned to one of three groups ( 10 subjects per group) requiring either a 50% MVC, 75% MVC or 100% MVC. Each subject's maximal voluntary contraction with a right handgrip was determined. This was followed by a 5-minute recovery period. Then 15-seconds of resting (pre-contraction) ECG's were recorded. Immediately followed by the recording of 10-seconds of contraction ECG's and muscular tensions, and 15-seconds of recovery ECG's. Cycle length and muscular tension values were obtained from the recording paper and cycle time, relative change in cycle time and 67 actual change in cycle time were calculated from the appropriate values. Analysis of variance of the results indicated that, during the pre-contraction phase, the "inspire" command caused maximum tachy-cardia to occur at beat 8 and maximum bradycardia to occur at either beat 10 or beat 1 of the contraction phase. The statement that maximum bradycarida may have occurred at beat 1 of the contraction phase i s supported by the fact that some subjects had negative values for their relative change in cycle time for this beat. The trend analyses of paired comparisons for the three groups showed that the linear trend for the 100% MVC group was significantly different from the linear trends for the 50% and 75% MVC groups (p<.01). However, the linear trend for the 75% MVC group was not significantly different from the linear trend for the 50% MVC group due to the vir t u a l abscence of a linear trend for the 50% MVC group. The Newman-Keuls analyses of RCCT for the three groups indicated that the cardioacceleratory response was composed of two phases and supported previous studies which postulated the existence of a fast-acting central heart-trigger mechanism and a slower-acting peripheral heart-trigger mechanism. The trend analyses F-ratios indicated that the use of RCCT as a dependent variable, generally, resulted in a smaller unexplained 68 variance than either CT C or ACCTC. A graphic plot of means for RCCT indicated a pronounced linear trend for the 100% MVC group, a slight linear trend for the 50% MVC group and virtually no linear trend for the 75% MVC group. This showed that the rate of recovery from the cardioacceleratory response does not appear to be strongly dependent on the magnitude of the %MVC. 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B. "Human Cardiovascular Adjustments to Exercise and Thermal Stress," Physiological Reviews. 54(1):75-159, 1974. Sampson, P. Repeated Mea3ure3 Analysis of Variance (UBC BMDP2V), Health Sciences Computing Facility, University of California, L03 Angeles, 1974. Storms, L. H., and Acosta, F. X. "Effects of Dynamometer Tension on Stimulus Generalisation in Schizophrenic and Non Schizophrenic Patients," Journal of Abnormal Psychology, 83(2):204-207, 1974. Toda, N., and Shimamoto, K. "The Influence of Sympathetic Stimulation on Transmembrane Potentials in the S. A. Node," Journal of Pharmacology  and Experimental Therapy, 159:298-305, 1968. Tuttle, V/, W., and Horvath, M. "Comparison of Effects of Static and Dynamic Work on Blood Pressure and Heart Rate," Journal of Applied Physiology, 10(2):294-296, 1957-Winer, B. J. Statistical Principles in Experimental De3ign, 2nd Ed., New York: McGraw-Hill Book Co., 1971. APPENDIX A Individual Raw Score3 TABLE I 73 Age and Maximal Voluntary Contractions Maximal Voluntary Contractions (kgms.) Age Mean of Two Subject (Years) T r i a l 1 T r i a l 2 T r i a l 3 Highest 1 22 39.6 36.4 38.0 38.8 2 23 28.0 31.2 27.4 29.6 3 22 50.8 57,5 44.0 54.2 '4 21 40.6 32.0 42.0 41.3 50$ MVC 5 21 49.2 48.0 46.4 48.6 6 19 34.6 35.8 32.4 35.2 7 21 52.0 50.0 46.6 51.0 8 20 57.6 58.0 56.0 57.8 9 21 39.4 45.2 40.0 42.6 10 26 42.0 47.0 39.2 44.5 11 22 42.0 40.0 39.0 41.0 12 21 50.0 54.0 46.0 52.0 13 24 37.0 34.0 37.2 37.1 14 20 38.8 40.4 41.2 40.8 75$ MVC 15 21 58.0 61.2 59.0 60.1 16 28 49.6 41.0 52.0 50.8 17 25 56.6 54.0 58.0 57.3 18 24 46.0 42.0 42.6 44.3 19 23 54.6 49.4 58.0 56.3 20 22 38.2 39.6 39.0 39.3 21 22 49.0 52.0 56.0 54.0 22 28 36.4 40.0 35.0 38.2 23 21 44.0 50.4 49.6 50.0 24 20 51.4 42.4 53.8 52.6 100$ MVC 25 18 40.0 38.2 40.0 40.0 26 23 52.6 53.4 49.6 53.0 27 24 46.6 36.6 33.6 41.6 28 22 58.0 60.4 57.0 59.2 29 21 47.8 45.8 47.0 47.4 30 22 35.2 34.0 32.0 34.6 TABLE I I Resting Cycle Time (mi l l iseconds) Heart Beat 50$ 75$ Subject 1 2 3 4 5 6 7 8 9 10 1 1160 1135 1090 1170 1205 1.185 920 765 705 765 2 765 760 735 720 745 730 715 715 720 735 3 850 830 860 850 1420 1170 1165 1115 1070 1020 1120 1285 1100 1310 1100 1235 990 920 895 1015 MVC I 780 760 735 765 775 750 725 710 730 815 1020 1030 1070 1015 1100 930 920 905 830 950 7 660 740 745 700 615 585 575 620 830 895 8 1110 1100 1000 985 1060 1165 995 905 875 885 9 785 790 785 800 780 765 755 770 785 790 10 1110 1025 965 935 955 960 790 780 850 940 11 865 855 850 865 830 760 695 735 765 785 12 790 795 750 760 705 700 700 710 740 785 13 960 1025 1015 950 995 1055 1025 905 845 890 765 775 800 840 800 725 735 795 810' 830 MVC H 745 730 760 925 1155 1010 875 815 790 870 1320 1250 1195 1265 1270 1190 1130 900 950 1350 17 1010 1020 985 1005 960 875 850 810 860 1000 18 910 900 925 880 940 810 735 775 900 940 19 1005 920 870 910 965 970 870 885 970 1050 20 860 950 865 920 865 835 860 765 950 1040 100$ MVC 21 885 925 925 875 825 770 760 790 840 870 22 765 830 860 810 795 785 690 685 805 965 23 950 865 925 930 865 735 640 560 580 990 24 635 625 630 630 640 620 610 600 600 610 25 870 920 945 945 950 900 870 850 825 880 26 710 705 710 710 715 700 680 680 715 775 27 1090 1170 1210 1020 1150 1180 1130 990 945 1075 28 1150 1115 1065 1065 1015 955 985 1010 950 950 29 915 910 850 860 905 940 865 825 830 850 30 790 840 815 790 775 780 650 695 685 735 TABLE I I I Contraction Cycle Time (mi l l iseconds) ON Heart Beat Subject 1 2 3 4 5 6 7 8 9 10 50$ MVC 1 940 980 985 1060 1110 1115 1130 1135 1100 1070 2 740 725 725 725 720 720 720 725 725 740 3 970 940 935 940 960 965 985 990 1000 1010 4 1360 1040 950 960 1025 1055 980 940 895 880 5 850 845 840 815 780 765 770 750 740 730 6 1000 980 960 1000 1025 955 950 950 895 930 7 820 770 755 750 740 720 710 730 725 720 8 900 900 915 915 900 895 885 865 885 900 9 750 700 680 670 645 640 660 670 720 730 10 920 850 845 830 830 820 780 780 775 775 11 780 770 850 840 810 815 825 830 830 835 .12 770 750 725 700 690 680 680 670 660 655 13 985 910 895 885 855 840 825 825 780 775 14 • 845 825 820 845 840 810 815 840 840 835 15 825 760 760 780 795 750 765 765 735 745 16 1250 1150 1115 1085 1080 985 965 910 890 915 17 960 920 940 955 8907 840 815 800 790 780 18 910 905 910 890 . 880 830 790 780 750 735 19 910 820 790 775 790 765 740 740 715 700 20 1025 925 1015 970 970 930 825 805 855 945 100$ MVC 21 860 775 725 660 22 830 710 640 590 23 900 755 710 590 24 620 620 600 570 25 935 910 880 825 26 810 750 715 680 27 1060 950 860 800 28 1010 955 900 885 29 900 790 700 655 30 780 720 665 640 630 630 635 630 630 630 560 545 530 520 510 510 550 535 525 515 505 510 565 550 540 535 530 525 790 805 810 755 730 725 655 625 610 590 580 570 790 785 775 . 765 750 790 850 850 825 815 810 820 630 610 595 590 580 570 615 610 595 585 585 580 TABLE IV CO C o n t r a c t i o n Muscu la r Tens ion ( k i l o g r a m s ) S u b j e c t 1 2 3 4 1 OcO 4.0 18.0 18.0 2 0.0 14.0 14.0 14.0 3 0.0 27.0 24.0 25.2 4 0.0 10.0 20.2 21.2 , 5 0.0 14.0 20.4 20.4 : 6 0.0 18.0 18.0 18.0 7 0.0 22.0 24.8 24.8 8 0.0 15.4 2 8 . 6 30.0 9 0.0 10.2 18.0 21.0 10 0.0 20.0 22.4 22.8 Heart Beat 5 6 7 8 9 10 18.0 18.0 18 .0 18.0 18.0 13.6 13.4 13.2 13.2 13.0 25.0 25.2 25.2 25.2 25.2 20.0 20.0 20.0 20.0 20.0 20.4 20.4 20.4 20.4 20.4 18.0 18.0 18.0 18.0 18.0 24.8 24.8 24.8 24.8 24.8 30.2 30.2 32.0 32.0 31.2 21.0 21.0 21.0 21.0 21.0 23.0 22.8 23.0 23.0 23.0 5C#MVC 18.0 14.0 25.0 21.2 20.4 18.0 24.8 30.2 21.0 22.8 75$MVC 11 12 13 14 15 16 17 18 19 20 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 0 0 0 0 . 0 20.6 27.2 22.8 19.6 29.2 39.8 30.8 32.0 42.6 25.0 3 0 . 8 35.2 27.0 29.0 46.0 40.6 43.4 33.0 42.6 30.6 30.8 35.6 28.0 31.6 46.4 40.6 41.0 33.0 42.6 28.0 3 0 . 8 3 6 . 6 2 8 . 0 31.6 4 6 . 0 3 8 . 0 4 0 . 6 3 3 . 0 42.6 2 8 . 4 30.6 3 6 . 6 28 .0 3 1 . 6 4 6 . 0 3 8 . 4 41 .0 33 .0 42.4 2 8 . 2 30.4 36.4 28.0 31.6 46.0 37.0 41.0 33.0 42,4 28.6 3 0 . 0 3 6 . 4 27.2 3 1 . 6 4 5 . 4 3 8 . 0 4 0 . 8 3 3 . 0 4 1 . 4 29.0 30.0 3 6 . 4 28.0 3 1 . 6 4 5 . 4 38.0 41.0 33.0 4 1 . 6 29.2 29.6 3 6 . 4 2 8 . 0 3 1 . 6 4 5 . 2 3 8 . 0 4 1 . 0 3 3 . 0 4 3 . 4 29.2 100$MVC 21 0.0 30.0 46.0 53.6 22 0.0 26.0 36.0 36.0 23 0.0 32.0 47.0 48.0 24 0.0 26.0 43.0 52.0 25 0.0 9.0 30.0 36.0 26 0.0 12.0 30.0 44.0 27 0.0 15.0 35.6 40.6 28 0.0 36.0 53.2 54.0 29 0.0 27.2 48.0 48.0 30 0.0 30.6 32.4 32.4 53.6 53.6 53.6 53.6 53.6 52.0 36.4 37.2 37.4 37.4 37.8 37.8 48.0 48.0 48.0 48.0 48.0 48.0 52.0 52.0 52.0 52.0 52.0 52.0 37.2 37.2 36.6 36.6 36.6 36.4 50.0 51.4 51.6 51.6 54.0 54.0 40.6 40.6 40.6 40.6 40.6 40.6 54.0 54.0 54.0 54.0 54.0 54.0 48.0 48.0 48.4 48.4 48.4 48.4 32.4 32.2 32.2 32.0 32.0 32.2 TABLE V CO o Recovery Cycle Time (mi l l iseconds) Subject Heart Beat 5 50$ MVC 1 2 3 4 5 6 7 8 9 10 1040 770 1025 830 760 950 770 870 705 825 1050 760 1015 990 800 965 880 950 685 810 1120 750 1015 1230 790 1190 885 1000 750 880 1115 760 1035 1155 805 925 890 980 770 905 1110 770 1065 1100 840 945 910 1010 745 910 6 7 8 9 10 1085 1090 1105 1120 1135 755 740 735 760 815 1105 1125 1105 1100 1100 1110 1020 990 1160 1110 835 870 885 865 845 950 945 880 970 1000 895 920 875 920 970 990 1020 990 1110 1160 750 795 830 820 730 900 885 875 890 855 75$ MVC 11 845 845 815 820 12 695 866 955 975 13 760 825 905 950 14 1055 1055 835 720 15 700 750 740 715 16 880 925 1060 1010 17 840 980 985 950 18 790 840 885 915 19 700 700 705 705 20 870 990 1130 1105 820 835 810 825 850 840 965 895 825 820 810 780 885 820 865 885 840 820 655 775 865 770 840 790 710 740 710 795 870 835 1025 980 950 985 925 875 900 830 840 910 950 900 900 840 950 950 960 985 700 720 740 730 740 780 975 1135 1145 1010 915 1065 21 565 585 615 640 650 635 620 655 655 650 22 435 445 435 430 430 520 680 730 825 960 23 470 475 510 840 935 955 925 930 950 970 24 465 470 480 475 485 500 530 1420 900 840 25 ' 695 725 790 840 815 780 840 800 795 815 26 615 630 665 705 755 750 760 700 700 670 27 825 845 910 1005 960 950 1125 1020 1095 980 28 795 795 825 920 910 915 935 935 900 910 29 890 1135 1130 1000 1040 1120 1125 1060 1080 1090 30 540 585 740 890 780 825 905 990 1005 975 82 APPENDIX B Individual Computed Scores TABLE I 00 LO Contraction - Actual Change i n Cycle Time (milliseconds) Heart Beat Subject 1 2 3 4 5 6 7 8 9 10 1 ^175 - 2 1 5 -220 - 2 9 5 -345 -350 -365 -370 -335 -305 2 -5 10 10 10 15 15 15 10 10 -5 3 50 80 85 8 0 60 55 35 30 20 10 4 -345 -25 65 55 -10 -40 35 75 120 135 <cn* mm 5 "35 - 3 0 -25 0 35 50 45 65 75 85 5 0 % M V L 6 _ 5 Q -30 -10 -50 -75 -5 0 0 55 20 7 75 125 140 145 155 175 185 165 170 175 8 - 1 5 -15 -30 -30 -15 -10 0 20 0 -15 9 40 90 110 120 145 150 130 120 70 60 10 20 90 95 110 110 120 160 160 165 165 11 12 13 14 75$ MVC 11 17 18 19 20 5 15 -65 -55 -25 -30 -40 -45 -45 -50 15 35 60 85 95 105 105 115 125 130 -95 -20 -5 5 35 50 65 65 110 115 -15 5 10 -15 -10 20 15 -10 -10 -5 45 110 110 90 75 120 105 105 135 125 100 200 235 265 270 365 385 440 460 435 40 8 0 60 45 110 160 185 200 210 220 30 35 30 50 60 110 150 160 190 205 140 230 260 275 260 285 310 310 335 350 15 115 25 70 70 110 215 235 185 95 CAOlAlAUMAOO>rt -tiAtoooiAOconco^ CM - * - - * H O J CM H W H 0 > A I A O O I A I A O O O - * U N 00 CO UN O CM - * C-- U N CM - * - * H r H n H N H O U M A U M A 1 A O I A O O CM - * - * r H r H ON r H CM r H I A I A I A O O ' A Q ' A ' A O ON O N V O r>-fv_vo o cy U N - * rH ON H CM rH CM - * - * O O U N O U N O O O O U N - J - CM i r \ O f > i r i O v O < l - N C M - * - * r H CM H CM H O U N O U N O O U N O O O - * O - J - - * O N C M C 0 O C M C M C M - * - * H CM r H CM r H O " N O O UN UN UN UN UN UN r H C ~ - 0 - * U N O N C ~ - v O O N O CM ON - * CM H U N U N O O O O U N O O O - * CM CO r H vO r H U N U N t ^ -H O N CM CM <H U N U N U N O O U N U N U N O U N ON UN ON <H ON CM CM I O H CM CM I I r H O U N O O U N U N U N O O U N r H t i l I I I H CM f / \ - J i A v O !>CO O O C M C M C M C M C M C M C M C M C M O N O O r H TABLE II 00 Contraction - Relative Change in Cycle Time (per cent) Heart Beat Subject 1 2 3 4 5 6 7 8 9 10 50$ MVC 1 ,-22.88 -28.10 -28.76 -38.56 -45.10 -45.75 -47.71 -48.37 -43.79 -39.87 2 -0.68 1.36 1.36 1.36 2.04 2.04 2.04 1.36 1.36 -0.68 3 4.90 7.84 8.33 7.84 5.88 5.39 3.43 2.94 1.96 0.98 t -33.99 -2.46 6.40 5.42 -0.99 -3.94 3.45 7.39 11.82 13.30 5 -4.29 -3.68 -3.07 0.00 4.29 6.13 5.62 7.98 9.20 10.43 6 -5.26 -3.16 -1.05 -5.26 -7.89 -0.53 0.00 0.00 5.79 2.11 7 8.38 13.97 15.64 16.20 17.32 19.55 20.6? 18.44 18.99 19.55 8 -1.69 -1.69 -3.39 -3.39 -1.69 -1.13 0.00 2.26 0.00 -1.69 9 5.06 11.39 13.92 15.19 18.35 18.99 16.46 15.19 8,86 7.59 10 2.13 9.57 10.11 11.70 11.70 12.77 17.02 17.02 17.55 17.55 75$ MVC 11 12 13 14 15 16 17 18 19 20 -.64 1.91 -10.67 -1.81 5.17 7.41 4.00 3.19 13.33 1.44 1.91 4.46 -2.25 -.60 12.64 14.81 8.00 3.72 21.90 11.06 -8.28 7.64 -0.56 1.20 12.64 17.41 6.00 3.19 24.76 2.40 -7.01 10.83 -.56 -1.81 10.34 19.63 4.50 5.32 26.19 6.73 -3.18 12.10 3.93 -1.20 8.62 20.00 11.00 6.38 24.76 6.73 -3.82 13.38 5.62 2.41 13.79 27.04 16.00 11.70 27.14 10.58 -5.10 13.38 7.30 1.81 12.07 28.52 18.50 15.96 29.52 20.67 -5.73 14.65 7.30 -1.20 12.07 32.59 20.00 17.02 29.52 22.60 -5.73 15.92 12.36 -1.20 15.52 34.07 21.00 20.21 31.90 17.79 -6.37 16.56 12.92 -0.60 14.37 32.22 22.00 21.81 33.33 9.13 100$ MVC 21 1.15 10.92 16.67 24.14 22 13.99 26.42 33.68 38.86 23 9.09 23.74 28.28 40.40 24 -1.64 -1.64 1.64 6.56 25 , -6.25 -3.41 0.00 6.25 26 -4.52 3.23 7.74 12 .26 27 1.40 11.63 20.00 25.58 28 -6.32 -0.53 5 .26 6.84 29 -5.88 7.06 17.65 22.94 30 -6.12 2.04 9.52 12.93 27.59 27 . 5 9 27 . 0 1 27 . 5 9 27 .59 27 .59 41.97 43.52 45-08 46.11 47.15 47.15 44.44 45.96 46.97 47.98 48.99 48.48 7.38 9.84 11.48 12.30 13.11 13.93 10.23 8.52 7.95 14.20 17.05 17 . 6 1 15.48 19 .35 21.29 23 . 8 7 25 .16 26.45 26.51 26.98 27 . 9 1 28.84 30.23 26.51 10.53 10.53 13.16 14.21 14.74 13.68 25 .88 28.24 30.00 30.59 31.76 32.94 16.33 17 . 0 1 19.05 20.41 20.41 21.09 TABLE I I I Contraction - Re lat ive Muscular Tension *(per cent) CO Subject Heart Beat 5 8 10 50$ MVC 1 2 3 4 5 6 7 8 9 10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10.31 47.30 49.87 24 . 2 1 28.81 51.14 43.14 26.64 23 .94 44.94 46.39 47.30 44.33 48.91 41.98 51.14 48.63 49.48 42.25 50.34 46.39 47.30 46.55 51.33 41.98 51.14 48.63 51.90 49.30 51.24 46.39 47 . 3 0 46 . 1 3 51.33 41.98 51.14 48.63 52.25 49.30 51.24 46.39 45.95 46 . 1 8 48.43 41.98 51.14 48.63 52.25 49.30 51.69 46.39 45.27 46.55 48.43 41.98 51.14 48,63 52.25 49 . 3 0 51.24 46.39 44.59 46.55 48.43 41.98 51.14 48.63 55.36 49.30 51.69 46.39 44.59 46.55 48.43 41.98 51.14 48.63 55.36 49.30 51.69 46.39 43.92 46.55 48.43 41.98 51.14 48.63 53.98 49.30 51.69 11 0.00 50.24 75.12 75.12 75.12 74.63 74.15 73.17 73.17 72 . 2 0 12 0.00 52.31 67.69 68.46 70.38 70.38 70.00 70.00 70.00 70.00 13 0.00 61.46 72 .78 75.47 75.47 75.47 75.47 73.32 75.47 75.47 14 0.00 48.04 71.08 77.45 77.45 77.45 77.45 77.45 77.45 77.45 15 0.00 48.59 76.54 77.20 76.54 76.54 76.54 75.54 75.54 75.21 75$ MVC ^ . 0.00 78.35 79.92 79.92 74.80 75.59 72 .83 74.80 74.80 74.80 17 0.00 53.75 75.74 71.55 70.86 71.55 71.55 71.20 71 .55 71.55 18 0,00 72.23 . 74.49 74.49 74.49 74.49 74.49 74.49 74.49 74.49 19 0.00 75.67 75.67 75.67 75.67 75.31 75.31 73.53 73.89 77.09 20 0.00 63.61 77.86 71.25 72 .26 71.76 72 .77 73.79 74.30 74.30 V 21 0.00 55.56 22 o.co 68.06 23 0.00 64.00 24 0.00 49.43 2 C - 0.00 22.50 100$ MVC 2 o 0.00 22.64 27 0.00 36.06 28 0.00 60.81 29 0.00 57.38 30 0,00 88.44 85.19 99.26 99.26 99.26 94.24 94.24 95.29 97.38 94.00 96.00 96.00 96.00 81.75 98.86 98.86 98.86 75.00 90.00 93.00 93.00 56.60 83.02 94.34 96.98 85.58 97.60 97.60 97.60 89.86 91.22 91.22 91.22 101.27 101.27 101.27 101.27 93.64 93.64 93.64 93.06 99.26 99.26 99.26 96.30 97.91 97.91 98.95 98.95 96.00 96.00 96.00 96.00 98.86 98.86 98.86 98.86 91.50 91.50 91.50 91.00 97.36 97.36 101.89 101.89 97.60 97.60 97.60 97.60 91.22 91.22 91.22 91.22 102.11 102,11 102,11 102.11 93.06 92.49 92.49 93.06 00 oo T A B L E I V Recovery - Actual Change i n Cycle Time (mi l l iseconds) CO Heart Beat 50$ Subject 1 2 3 4 5 6 7 8 9 10 A -275 -285 -355 -350 -345 -320 -325 -340 -355 -370 2 -35 -25 -15 -25 -35 -20 -5 0 -25 - 8 0 3 -5 5 5 -15 -45 -85 . -105 -85 -80 - 8 0 4 185 25 -215 -140 -85 -95 25 -145 -95 v 5 55 15 25 10 -25 -20 -55 -70 -50 -30 C 6 0 -15 -240 25 5 0 70 -20 -50 7 125 15 10 5 -15 0 -25 20 -25 -75 8 15 -65 -115 -95 -125 -105 -135 -105 -225 -275 9 85 105 40 20 45 40 -5 - 4 0 -30 60 10 115 130 60 35 30 40 55 65 50 85 75$ MVC 11 -60 -60 -30 -35 -35 -50 -25 -40 -65 -55 12 90 - 8 1 -170 -190 -180 -110 -40 -35 -25 5 13 130 65 -15 -60 5 70 25 5 50 70 14 -225 -225 -5 110 175 160 55 -35 60 : -10 40 15 170 120 130 155 130 160 75 0 35 16 470 425 290 340 325 370 400 365 425 475 17 160 20 15 50 100 170 160 90 50 100 18 150 100 55 25 40 100 -10 -10 -20 -45 19 350 350 345 345 350 330 310 320 310 270 20 170 50 -90 -65 65 -95 -105 30 125 -25 100$ MVC 21 305 285 255 230 220 235 250 215 215 220 22 530 520 530 535 535 445 285 235 140 5 23 520 515 480 150 . 55 35 65 60 40 20 24 145 140 130 135 125 110 80 -810 -290 -230 25 . 185 155 90 40 65 100 40 80 85 65 26 160 145 110 70 20 25 15 75 75 105 27 250 230 165 70 115 125 -50 55 -20 95 28 155 155 125 30 40 35 15 15 50 40 29 -40 -285 -280 -150 -190 -270 -275 -210 -230 -240 30 195 150 -5 -155 -45 -90 -170 -255 -270 -240 ' T A B L E -V Recovery - Rslative Change i n Cycle Time (per cent) Subject Heart Beat 5 8 10 50$ MVC 1 2 3 4 5 6 7 8 9 10 -35.95 -37.25 -46.41 -45.75 -45.10 -41.83 -42.48 -44.44 -46.41 -48.37 -4.76 -3.40 -2.40 -3.40 04.76 -2.72 -0.68 0.00 -3.40 -10.88 -0.49 0.49 0.49 -1.47 -4 .41 -8.33 -10.29 -8.33 -7.84 -7.84 18.23 2.46 -21.18 -13.79 -8.37 -9.36 -0.49 2.46 -14.29 -9.36 6.75 1.84 3.07 1.23 -3.07 -2.45 -6.75 -8.59 -6.13 -3.68 0.00 -1.58 -25.26 2.63 0.53 0.00 0.53 7.37 - 2 . i l -5.26 13.97 1.68 1.12 0.56 -1.68 0.00 -2.79 2.23 -2.79 -8.38 1.69 -7.34 -12.99 -10.73 -14.12 -11.86 -15.25 -11.86 -25.42 -31.07 10.76 13.29 5.06 2.53 5.70 5.06 -0.63 -5.06 -3.80 7.59 12.23 13.83 6.38 3.72 3.19 4.26 5.85 6.91 5.32 9.04 11 -7.64 -7.64 -3.82 -4.46 -4.46 -6.37 t-3.18 -5.10 -8.28 -7.01 12 11.46 -10.32 -21.66 -24.20 -22.93 -14.01 -5.10 -4.46 -3.18 0.64 13 14.61 7.30 -1.69 -6.74 0.56 7.87 2.81 0.56 5.62 7.87 14 -27.11 -27.11 -0.60 13.25 21.08 6.63 -4.22 7.23 -1.20 4.82 15 19.54 13.79 14.94 17.82 18.39 : 14.94 18.39 8.62 0.00 4.02 16 34.81 31.48 21.48 25.19 24.0? 27.41 29.63 27.04 31.48 35.19 17 16.00 2,00 1.50 5.00 10.00 17.00 16.00 9.00 5.00 10.00 18 15.96 10,64 5.85 2.66 4.26 10.64 -1.06 -1.06 -2.13 -4.79 19 33,33 33.33 32.86 32.86 33.33 31.43 29.52 30.48 29.52 25.71 20 16,35 4.81 - 8 0 65 -6.25 6.25 -9.13 -10.10 2.88 12.02 -2.40 21 35.06 32.76 29.31 26.44 25.29 27.01 28.74 24.71 24.71 25.29 22 54.92 53.89 54.92 55.44 55.44 46.11 29.53 24.35 14.51 0.52 23 52.53 52.02 48.48 15.15 5.56 3.54 6.57 6.06 4.04 2.02 24 23.77 22.95 21.31 22.13 20.49 18.03 13.11 -132.79 -47.54 -37.70 25 21.02 17.61 10.23 4.55 7.39 11.36 4.55 9.09 9.66 7.39 26 20.65 18.71 14.19 9.03 2.58 3.23 1.94 9.68 9.68 13.55 27 23.26 21.40 15.35 6.51 10.70 11.63 -4.65 5.12 -1.86 8.84 28 16.32 16.32 13.16 3.16 4.21 3.68 - 1.58 1.58 5.26 4.21 29 -4 .71 -33.53 -32.94 -17.65 -22.35 -31.76 -32.356 -24.71 -27.06 -28.24 30 26.53 20.41 -0.68 -21.09 -6.12 -12.24 -23.13 -34.69 -36.73 -32.65 VO to 93 APPENDIX C ANOVA. Paired Comparisons of RCCTQ f o r the Three le v e l s of $MVC TABLE I 94 Summary of ANOVA Contraction - Relative Change i n Cycle Time (RCCTC) Comparison 50$ MVC Vs. 75$ MVC Source df MS F P Between Subjects 19 $MVC 1 4555,7 2.77 NS Ss w . $MVC 18 1644.2 Within Subjects 180 Beats 9 220.6 8.23 <.01 B e a t 3 ( l i n . ) 1 1720.9 12.01 <.01 B e a t s ( q u a d . ) 1 64.3 1.77 NS $MVC x Beats 9 46.5 1.74 NS Beats x Ss w. $MVC 162 26.8 Beats x Ss w. $MVC( l i n j 18 143.3 Beats x S s w. $ M V C ( q u a d 0 18 36.4 * NS denotes that the F-ratio i a not s i g n i f i c a n t at the 0.01 l e v e l of confidence. 95 TABLE I I Summary of ANOVA Contraction - Relative Change i n Cycle Time (RCCT,,) Comparison 50$ MVC Vs. 100$ MVC Source df MS F P Between Subjects 19 $MVC 1 16796.1 8.94 < .01 Ss $MVC 18 1873.7 Within Subjects 180 Bes-ta 9 656.9 29.07 <.01 B c a f c s ( I i n . ) B e a t s ( q u a d . ) $MVC x Beats 1 1 9 4837.3 871.8 287*6 43.64 19.00 12.73 <.01 <.01 <.01 $MVC x 3eat3p.. n v $MVC x B e a t 3 ( q u a d s ) Beats x Ss w. $MVC 1 1 162 . 2132.1 394.4 22.6 19.24 8.60 < .01 <c01 Beats x Ss w. $MVC^ i n % Beats x Ss w. $ M V G ( q u a d j 18 18 110.9 45.9 * NS denotes that the F-ra t i o i s not s i g n i f i c a n t at the 0.01 l e v e l of confidence. TABLE I I I 96 Summary of ANOVA Contraction - Relative Change i n Cyele Time (RCCTC) Comparison 75$ MVC Vs. 100 $MVC Source df MS P Between' Subjects 19 $MVC 1 3856.9 3.43 NS Ss w. $MVC 18 1124.4 Within Subjects 180 Beats 9 948.4 73.71 <.0i B 8 3 t 3 ( l i n . ) 1 7684.0 111.49 <.01 Beats^quadj 1 777.2 41.07 <.01 $MVC x Beats 9 158.3 12.30 <.01 $MVC x B e a t 3 ( i i n . ) 1 787.8 11,43 <.01 $MVC x B e a t s ( q u a d # ) 1 462.6 24.45 <.01 Beats x Ss w. $MVC 162 12.87 Beats x Ss w. %NSC^n ^ 18 68.9 Beats x S s w. $ M V C ( q u a d ) 18 18.9 * NS denotes that the F-ra t i o i 3 not s i g n i f i c a n t at the 0.01 l e v e l of confidence. APPENDIX D Recovery Condition - Means and Standard Deviations of Cycle Time and Actual Change i n Cycle Time with Graphical Presentations TABLE I Recovery Condition - Means and Standard Deviations of Cycle Time (CT R) Expressed i n Milliseconds for a l l Groups and a l l 10 Heart Beats. Heart Beat Group 1 2 3 4 5 6 7 8 9 10 50$ MVC 854.5 ±115.4 890.5 ±122.0 961.0 ±178.07 934.0 ±137.7 940.5 ±130.7 937.5 ±135 .3 941.0 ±124.2 927.0 ±118.8 971.5 ±142.0 972.0 ±153.2 75$ MVC 813.5 ±111.0 877.5 ±110.6 901.5 ±135.0 886.5 ±139.1 853.5 ±127.6 857.0 ±122.9 870.0 ±123.6 868.0 ±94 .7 970.0 168.5 867.0 ±93.9 100$ MVC 629.5 ±163.5 669.0 ±213.5 710.0 ±215 .1 774.5 ±205.0 776.0 ±202.5 795.0 ±200.3 844.5 ±199.8 ^924.0 ±224.5 890.5 ±149.0 886.0 ±141.8 99 FIGURE 1 T 1,1 1 I ,i.„l-l-t.-L.L. Heart Beat Recovery Condition - Change in Cycle Time during the f i r s t 10 Heart Beats. TABLE I I Recovery Condition - Means and Standard Deviations of Actual Change in Cycle Time (ACCTR) Expressed i n Milliseconds for a l l Groups and a l l 10 Heart beats. Group 1 2 3 4 Heart Beat 5 6 7 8 9 10 50$ MVC 26.5 1126.2 1112.8 -80.0 ±143.5 -53.0 1118.4 -59.5 1112.3 -56.5 1106.3 -60.0 ll08.3 -46.0 ±119.9 -90.5 ±120.1 -91.0 ±138.0 75$ MVC .140.5 -191.8 ,76.5 1193.5 , 52.5 1161.2 , 67.5 -174.3 ,100.5 ±160.8 ,97.0 ±163.0 , 84.0 ±167.3 , 86.0 -142.5 , 84.0 ±160.6 . 87.0 ±165.4 100$ MVC ,240.5 1174.1 ,201.0 3225.6 ,160.0 ±230.6 , 95.5 -196.5 . 94.0 -189.3 . 75.0 ±188.2 , 25.5 ±169.0 ,-54.0 ±308.5 .-20.5 -179.2 ,-16.0 -163.4 1 o o 101 FIGURE Z Heart Beat Recovery Condition - Change i n Actual Change i n Cycle Time during the f i r s t 10 Heart Beats. 

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