Specificity of Speed of Exercise. MARY T. MOFFROID, M.A. and ROBERT H. WHIPPLE, B.A PHYSICAL THERAPY

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1 Resistive exercise is employed to increase functional performance. Weight lifting has been the traditional program of resistive exercise to increase muscular force (strength). Ten years ago Hellebrandt found that the amount of work done is not as important as the rate at which it is done. The purpose of this study was to determine the specific effects on muscular endurance and on muscular force of two different training speeds. The two training programs administered to two different groups were slow maximal exercise (low power) and rapid maximal exercise (high power). Speed of exercise was found to be specific for muscular endurance and for force increases at and below the exercise speed. Specificity of Speed of Exercise MARY T. MFFRID, M.A. and RBERT H. WHIPPLE, B.A. T, en years ago Hellebrandt found that increasing the speed at which an exercise was performed was as effective for increasing the work capacity as increasing the load. Work capacity is defined as the length of the excursion times the number of repetitions times the load. The work per unit of time (power) was equivalent in two training programs: high speed low load and low speed high load. 1 DeLorme attempted to determine if there was any relation between ability to lift weights and the ability to move a limb rapidly. He, as well as others, has not shown any evidence that weight lifting increases a muscle's rate of contraction. 2-3 Similarly, de Vries maintained that strength and endurance were, to a degree, independent of each other in that endurance could vary when strength was held constant. 4 Mrs. Moffroid, who was Unit Supervisor, Kinesiology Research Section, Physical Therapy Department, Institute of Rehabilitation Medicine, New York University Medical Center at the time this study was completed, is now at Downstate Medical Center, State University of New York, Brooklyn, New York Mr. Whipple is Senior Physical Therapist, Physical Therapy Research Section, Institute of Rehabilitation Medicine, New York University Medical Center, New York, New York This paper is adapted in part from a thesis written for the degree of Master of Arts from New York University, New York. This investigation was supported in part by research grant RT-1 (c6) from the Social and Rehabilitation Services, Department of Health, Education, Welfare, Wasnington, D.C. under the designation of New York University as a Rehabilitation and Training Center, and in part from grant FR00291 from the United States Public Health Service PHYSICAL THERAPY

2 TABLE 1 PRETEST RDER F TEST VELCITIES IN REVTINS PER MINUTE Group I Mon. Wed. Fri. Mon. Wed. Fri. 5 subjects 0-3 rpm 6 rpm 9 rpm 12 rpm 15 rpm 18rpm 5 subjects 18 rpm 15 rpm 12 rpm 9 rpm 6 rpm 0-3 rpm Group II 5 subjects 0-3 rpm 6 rpm 9 rpm 12 rpm 15 rpm 18 rpm 5 subjects 18 rpm 15 rpm 12 rpm 9 rpm 6 rpm 0-3 rpm Group subjects 0-3 rpm 6 rpm 9 rpm 12 rpm 15 rpm 18 rpm 5 subjects 18 rpm 15 rpm 12 rpm 9 rpm 6 rpm 0-3 rpm The purpose of this study was to evaluate the effects of two different training speeds on muscular endurance and on mustular force. The two training programs administered to two different groups were slow maximal exercise (low power) and rapid maximal exercise (high power) given for two minutes, three times a week for six weeks. Increases in peak torque at six different velocities and increases in total work at the training speed were taken as indexes of improvement in muscular force (strength) and energy (muscular endurance) respectively. Time and velocity were the independent variables. Velocity of exercise was controlled by means of a constant speed (isokinetic) exercise device.* INSTRUMENTATIN The exercise device used in this study was electro-mechanical. It could be preset through electronic speed-control components to run at any constant speed between zero and twentyfive revolutions per minute. All input force applied to the input shaft at any operating speed would generate motion of the limb and shaft. Any tendency of the limb to accelerate beyond the preset speed would be absorbed by the mechanism, thereby holding the speed constant. This device has been shown to be valid and reliable for measurements made in this study. 5 Peak torque at different velocities of contraction (3, 6, 9, 12, 15, 18 revolutions per minute) was measured for the quadriceps and for the hamstring muscle group. Initially and finally, the work of every repetition in the twominute exercise period was calculated, added, and the sum was divided by the total number of seconds the muscle group was actually contracting. This value was called energy (total work in a given period of time, or average power) and was the operational definition of endurance for this study. Thus, muscular endurance was defined as the average power output over a given period of time. It could be quantified in units of newton meters f of work per second for two minutes. PRCEDURE The basic format of the study was to administer a pretest, a specific training program, and a posttest. Two experimental exercise groups (one exercising at a low power output, the other at a high power output) were compared with each other in terms of torque increases and endurance increases. The control group constituted a third group and received no exercise Thirty subjects were randomly selected from the staff of the Institute of Rehabilitation Medicine, New York University Medical Center. The thirty subjects were then randomly assigned to one of three groups: an exercise group to work at slow velocities only (Group I), an exercise group to work at high velocities only (Group II), and a control group to receive no exercise (Group III). * Cybex, Manufactured by the Cybex Division of Lumex, Inc., Bayshore, New York t Newton meters of torque may be converted to foot pounds of torque by dividing by Volume 50 / Number 12, December

3 f the thirty subjects selected, six were males and twenty-four were females. This sample is consistent with the distribution of males and females on the staff of the rehabilitation center. Random assignment placed two males in Group I, one male in Group II, and three males in Group III. ne of the males in Group III withdrew in the first week because of an unrelated back injury. ne female in Group III also withdrew because of lack of interest and cooperation. Thus, the final sample comprised Group I with eight females and two males, Group II with nine females and one male, and Group III with six females and two males. The pretest consisted of six testing sessions in a two-week period. At each session the subject was asked to perform five maximal reciprocal contractions of the quadriceps and hamstring muscle groups at a specific constant velocity. The dominant leg (determined by dominant handedness) was tested and exercised. The test at zero revolutions per minute was given at 65 degrees (1.13 rad) of knee extension for the quadriceps and at 45 degrees (0.79 rad) of flexion for the hamstring muscle group. These positions were selected because they have been shown to be the joint angles where these muscle groups are able to produce the most torque. 6 The maximum contraction for this isometric test was held until the command to push harder yielded no higher torque reading on the pen recorder. In order that the data for untrained subjects would not be affected by day-to-day learning or strengthening, the order of the testing was staggered as shown in Table 1. The numbers refer to velocity in revolutions per minute. A three-minute rest was allowed between the isometric contraction and the dynamic series at three revolutions per minute. The selection of order a subject followed was random. The period of exercise consisted of two minutes of alternate extension and flexion at the knee joint without a rest. Maximal effort was requested. The subjects in the exercise groups exercised either at a slow speed (6 revolutions per minute) or at a fast speed (18 revolutions per minute). Those subjects who exercised at six revolutions per minute did approximately twenty repetitions in the two-minute period. Those who exercised at eighteen revolutions per minute did approximately sixty repetitions in the same time period. The training was performed every other day for six weeks. Most of the subjects were punctual, enthusiastic, and cooperative. Their time of exercise and testing was not allowed to vary by more than one hour. This was adhered to PAPE?SPEEl i 1.91 cms 7 mm.95 +cm Fig. I. Samples of two-minute exercise sessions at six revolutions per minute and at eighteen revolutions per minute. The high peaks represent peak torque of the quadriceps PHYSICAL THERAPY

4 because of the diurnal effects on strength observed by Hislop. 7 If a subject missed an exercise day, he was obliged to make it up on the following day. The stabilization and positioning utilized during the test and exercise sessions have been presented in an earlier publication. 5 The data collected from the pretest sessions consisted of the peak torque for the best out of five repetitions for each test velocity. The point in the range of motion where the subject was able to deliver the peak torque was noted. n the exercise days, a two-minute period of maximal exercise was recorded with the paper running at 1.91 centimeters per minute. nce during the first week and again during the last week the two-minute bout was recorded at 1.91 centimeters per second (Fig. 1). From these recordings, muscular endurance was measured as described previously. The posttest was conducted in the same manner as was the pretest. The same measurements were made of peak torque for the best out of five repetitions. The point in the range where the peak torque occurred was recorded. In addition, daily comments were recorded which were pertinent to a subject's attitude and performance. RESULTS The initial levels of peak torque for each of the three groups appear in Table 2. The values are in units of newton meters of torque and represent the mean of all the subjects in each group. Peak Torque Increases The mean increases in peak torque of the quadriceps are indicated in Table 3. The values represent the mean of each group for each test velocity. A two-way analysis of variance demonstrated a difference between increases made at the various test velocities (p<0.05). There was no significant interaction. Table 4 presents TABLE 2 INITIAL VAES F PEAK TRQUE FR QUADRICEPS Velocity Group I Mean + S.D. Newton Meters Group II Mean + S.D. Newton Meters Group III Mean + S.D. Newton Meters 0 rpm 3 rpm 6 rpm 9 rpm 12 rpm 15 rpm 18 rpm ± ± ± ± TABLE 3 MEAN INCREASES F PEAK TRQUE FR QUADRICEPS Group I Group II Group III Velocity Newton Meters Newton Meters Newton Meters 0 rpm rpm ,.9 6 rpm rpm 14, rpm 14, rpm 10,,8 12., rpm 8, ,.0 Volume 50 / Number 12, December

5 TABLE 4 SUMMARY F ANALYSIS F VARIANCE MAIN EFFECTS Source of Variation Sums of Squares Degrees of Freedom F ratio P Groups <0.01 Speeds <0.05 Interaction Error 40, SIMPLE MAIN EFFECTS Increases at the Test Velocities Velocity Sums of Squares Degrees of Freedom F ratio P 0 rpm rpm < rpm < rpm rpm rpm rpm Increases Made by the Exercise Groups Group Sums of Squares Degrees of Freedom F ratio p I <0.01 II III SLW MAXIMAL C 190 cr 180 h <5^ f - EXERCISE PRETEST PSTTEST H cr 100 o H ~i 12 ~T~ 15 n 18 VELCITY - R P M F/g. 2. Peafc torques of quadriceps plotted against velocity of contraction before (solid line) and after (dotted line) the slow maximal exercise regime PHYSICAL THERAPY

6 the simple main and main effects of the analysis of variance. Significant increases were evident at the test velocities of three and six revolutions per minute (p<0.01). The increases made by Groups II and III appeared to be rather uniform across all speeds. The increases made by Group C tr h- 0 H Z 1 3 <r o FAST MAXIMAL EXERCISE PRETEST PSTTEST VELCITY - R P M Fig. 3. Peak torques of the quadriceps plotted against velocity of contraction before (solid line) and after (dotted line) the fast maximal exercise regime. N EXERCISE C cr h o i- e- PRETEST PSTTEST DC VELCITY R P M Fig. 4. Peak torques of the quadriceps plotted against velocity of contraction for the pretest (solid line) and the posttest (dotted line) of the control group. Volume 50 / Number 12, December

7 TABLE 5 INCREASES IN ENERGY Group Initial Energy Mean±S.D. Final Energy Mean±S.D. I (low power) II (high power) 41±8 N-m/sec. 48± 12 N-m/sec. 45±8 N-m/sec. 62±8 N-m/sec. t 1.47 not significant t=2.36 p<0.02 I were not uniform across all speeds (p<0.01). Group I exercised at six revolutions per minute. Figure 2 presents peak torques for the quadriceps of Group I for all test velocities before exercise (solid line) and after exercise (dotted line). The ten subjects showed a significantly higher increase at three as well as at six revolutions per minute. They made slight gains at the higher velocities as shown in Figure 2. Group II exercised at eighteen revolutions per minute. Figure 3 illustrates initial and final values at all test velocities for the ten subjects in Group II. The solid line shows the torquevelocity. A two-way analysis of variance demshows the curve after exercise. Group III was the control group. The eight subjects in this group were tested twice, with a six-week interlude. Figure 4 presents the performance of this group on the pretest (solid line) and on the posttest (dotted line). Increases in Energy (Muscular Endurance) Table 5 lists the initial and final values of energy of the two exercise groups for the quadriceps muscle. Group II showed a larger increase in muscular endurance than did Group I (p<0.02). DISCUSSIN The isokinetic device used in this study provided for reciprocal exercise. Subjects exercised maximally in knee flexion and in knee extension; however, this study stressed the quadriceps muscle group for several reasons. First, this muscle has a distinct force variation through a range of motion and one can be relatively assured of correctly observing the peak torque and the point in the range of motion where it occurs. This is not as true for the hamstring muscle group. 6 Second, the quadriceps was exercised in the antigravity position and made more gains than did the hamstrings muscles. As Figure 1 indicates, the hamstring muscle group showed little fatigue after two minutes of maximal exercise, suggesting that, perhaps, in this position the knee flexors were not truly "overloaded." According to Hellebrandt, overloading is necessary to achieve maximal gains. 8 Third, the subjects appeared to concentrate on gains made in the muscles which extend the knee more than on gains made in the muscles which flex the knee. At each test velocity the initial values of peak torque were comparable among the subjects of all three groups (Tab. 2). The increase in newton meters of peak torque at all velocities, therefore, was used as the criterion in assessing force gains after exercise. Initially, the total work of the quadriceps in the two-minute period was equivalent in the two exercise groups, even though Group II performed three times as many repetitions as did Group I in the two-minute period. This equivalency was determined by a pilot study and served as the rationale for selecting the exercise speeds of six and eighteen revolutions per minute. The increases in peak torque have been mentioned. No gains at zero revolutions per minute were made by any of the three groups (Tab. 4). Variability in performance was greatest at this test velocity, the control group increasing as much at this speed as did the exercise groups, thus suggesting that these increased scores did not reflect increased muscular force but rather 1698 PHYSICAL THERAPY

8 decreased neuromuscular inhibition. This lack of force increase might be explained by the theory that dynamic exercise does not specifically increase static (isometric) force. 3 ' 9 The numerical increase in newton meters of peak torque at the exercise speed was higher in the low power exercise group (47.1 newton meters at 6 revolutions per minute versus 15.6 newton meters at 18 revolutions per minute for the high power exercise group). This finding also supports Gordon's work on rat skeletal muscle which showed that low power exercise increases myofibrillar components (strength) whereas high power exercise increases sarcoplasmic constituents (local endurance). 10 The joint position where the peak torque of the quadriceps occurred was also analyzed to ascertain if a period of exercise significantly altered this position. This was necessary because if any one group was able, through exercise, to develop a peak torque earlier in the range of motion (where the muscle is at greater length), one would be attributing a force increase to what, in effect, is only a result of a change in mechanical advantage. This, however, was not found to be a contributing factor. The work of each repetition during the twominute exercise period was computed to establish the average power rate for this time period. Because this part of the study was designed to compare the increases of the slow exercise group with the increases of the fast exercise group, any error of work measurement from pen lag at the fast speeds remained a constant error. $ The clinical application of this study is now being studied with two patient groups. The results thus far sueeest that velocity may be an important consideration in rehabilitation. SUMMARY AND CNCSIN The principle has been reiterated that the amount of work done is not as important as the rate at which it is done. In Hellebrandt's words, t With the recording system used at the time this study was carried out pen lag at fast velocities was responsible for a slight overmagnification of work curves. "Power is the variable on which extension of the limits of performance depends." 1 This study has further delineated that speed is the variable upon which the nature of this extension depends; that exercise is speed specific in the following ways: 1. Low power (low speed, high load) exercise produces greater increases in muscular force only at slow speeds. 2. High power (high speed, low load) exercise produces increases in muscular force at all speeds of contraction at and below the training speed. 3. High power exercise increases muscular endurance at high speeds more than does low power exercise increase muscular endurance at slow speeds. Acknowledgment. The statistical analysis was guided by Stuart Kahan, Ph.D. Initial pilot work for this study was assisted by a physical therapy research workshop, Downey, California, May REFERENCES 1. Hellebrandt FA: Methods of muscle training. Influence of pacing. Phys Ther Rev 2: , DeLorme T, Ferris B, Gallagher J: Effect of progressive resistive exercise on muscle contraction time. Arch Phys Med 33:86-92, Smith L, Whitley J: Influence of strengthening exercises on speed of limb movement. Arch Phys Med 46: , de Vries H: EMG fatigue curves in postural muscles: A possible etiology for idiopathic low back pain. Amer J Phys Med 47: , Moffroid M, Whipple R, Hofkosh J, et al: A study of isokinetic exercise. Phys Ther 49: , Williams M, Stutzman L: Strength variations through a range of motion. Phys Ther Rev 39: , Hislop H: Quantitative changes in human muscular strength. J Amer Phys Ther Ass 43:21-38, Hellebrandt FA: Application of overload principles to muscle training in man. Amer J Phys Med 37: , Hansen J: Training effects of dynamic maximal resistive exercise. Int Z Angew Physiol ein Schl Arbeitphysiol 19: , Gordon E, Kowalski K, Fritts M: Changes in rat muscle fiber with forceful exercises. Arch Phys Med 38: , 1967 Volume 50 I Number 12, December

9 SELECTED READINGS 1. Dern R: Forces exerted at different velocities in human arm movements. Amer J Physiol 15: , Eckert LH: A concept of force energy in human movement. Phys Ther 45: , Fenn W, Marsh BS: Muscular force at different speeds of shortening. J Physiol 85: , Hill AV: Heat of shortening and dynamic constants of muscle. Proc Royal Soc Med Series B, 126: , Hislop H, Perrine J: The isokinetic concept of exercise. Phys Ther 47: , Perrine J: Isokinetic exercise and the mechanical energy potentials of muscle. J Health Phys Ed Rec 39: 40-44, Wilkie DR: The relation between force and velocity in human muscle. J Physiol 110: , 1949 the authors Mary Moffroid, assistant professor of physical therapy, Downstate Medical Center, Brooklyn, New York, received her Master of Arts degree from New York University. Her thesis was based on the study reported in this paper. The study was done in the Kinesiology Research section of the Physical Therapy Department, Institute of Rehabilitation Medicine, New York, of which she was then supervisor. Mrs. Moffroid is currently matriculated in the Ph.D. program of rehabilitation education at New York University. Robert Whipple is senior physical therapist in the Physical Therapy Research Section of the Institute of Rehabilitation Medicine, New York University Medical Center. He received his certificate in physical therapy at Columbia University. Mr. Whipple is engaged in electromyographic research in the electrodiagnostic department of the institute. He is completing work in the master's degree program in physical therapy at New York University PHYSICAL THERAPY