Exercise Effect of Modified Contralateral Stabilization Bar During One-Legged Isokinetic Exercise

Transcription

1 177 Exercise Effect of Modified Contralateral Stabilization Bar During One-Legged Isokinetic Exercise Seong Woong Kang, MD, Jae Ho Moon, MD, Sae ll Chun, MD ABSTRACT. Kang SW, Moon JH, Chun S-I. Exercise effect of modified contralateral stabilization bar during one-legged isokinetic exercise. Arch Phys Med Rehabil 1995;76:75: We compared the electrical activities recorded from the muscles of the unexercised leg with changing the position of the contralateral stabilization bar to determine whether the degree of muscle contraction was influenced by the position of the bar during one-legged isokinetic exercise using an isokinetic dynamometer. The root mean square (RMS) values recorded from the medial hamstring sites of the unexercised legs showed a significantly higher value when the bar was located behind and on both in front of and behind the unexercised leg during one-legged extension exercise. Results from the isokinetic knee flexion exercise test indicated that a significantly greater RMS value was recorded from the vastus lateralis sites when the bar was located in front of and on both sides of the unexercised leg. During one-legged isokinetic extension-flexion exercise, the mean values of RMS voltage were greater when the bar was positioned in front of and on both sides of the unexercised leg in the vastus lateralis site. At the medial hamstring site, e. greater value was noticed when the bar was located behind or on both sides by the American Congress of Rehe.oil;'~uon Medicine and the American Academy of Physical Medicine and Rehabilitation Literature on strength and its development is extensive, ranging from the study of training techniques and their optimal prescriptions, to the factors that contribute to strength development such as neural and muscular factors. Various studies have been used to develop a more efficient means of strength gain with training. Among those studies, the study for the strength gain of one-limb exercise on the contralateral limb was designed to prevent the deterioration of muscle function during immobilization and to develop a more effective exercise program, t-6 The strength benefit in the untrained limb may relate to cross-educational effect and the associated movements to stabilize the body while exercise was being performed, t'2"4'7'8 The contralateral stabilization bar of the Cybex a isokinetic machine can provide stability of the body by limiting the associated movement of the unexercising leg during isokinetic exercise of the contralateral leg. Thus, relatively large resistance can be loaded on the unexercising leg whenever the bar limits the associated movement, which may permit more isometric contraction of the unexercised leg. To measure strength, researchers can use the electromyography by analyzing the electrical activity detected from a contracting muscle instead of using isometric, isotonic, or isokinetic muscle testing devices. 1"9-16 Several parameters of n~lyoelectrical signal were used in many studies to find out From the Department of Rehabilitation Medicine, Yongdong Severance Hospital (Drs. Kang, Moon), Yonsei University College of Medicine, Seoul, Korea; and the Department of Rehabilitation Medicine (Dr. Chun), Severance Hospital, Yonsei University College of Medicine, Seoul, Korea. Submitted for publication March 2, Accepted in revised form September 6, No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organizations with which the authors are associated. Reprint requests to Seong Woong Kang, MD, Department of Rehabilitation Medicine, Yongdong Severance Hospital, Yonsei University College of Medicine, #146-92, Dogok-Dong, Kangnam-Ku, Seoul , Korea by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation /95/ /0 whether any correlation existed between electrical activity and the force of a contracting muscle] '9't6 Among those parameters, the root mean square (RMS) value was known to be a parameter that more completely reflected the physiological correlates of the motor unit behavior during muscle contraction, 9'J2"17'18 and can be used as a substitute measure of force.lt'16't9 Even though the RMS value was widely used to study the relationship between the force and the electrical activity, it would be erroneous to generalize the results obtained from a specific muscle to other muscles or other experimental conditions, ~'t5 because many factors can affect the electromyographic signal-force relationship. ~2,17,2 So the electromyographic signal-force relationship must be primarily determined by the muscle investigated under the same condition.~l'52'15 The present study was initiated to determine the relation between RMS values and measured force outputs of knee extensors and knee flexors. Our second purpose was to investigate the effect in changing the position of the contralateral stabilization bar and determine how it influences the exercise effect of the uncxercised knee muscles by analyzing the myoelectrical signal recorded from those muscles during one-legged isokinetic exercise. Subjects METHOD Fifteen adult men, ranging between 24 and 28 years of age volunteered to be subjects for the investigation on the relationship between RMS value and the force of isometric contraction during increasing force of contraction. RMS voltage was obtained from 20 vastus lateralis and medial hamstring sites of the subjects. For the effect of one-legged isokinetic exercise on the contralateral unexercised leg, a control group of 27 adult men, ranging between 21 and 24 years, was studied. None of the subjects had any history of

2 178 MODIFIED CONTRALATERAL STABILIZATION BAR, Kang neuromuscular or skeletal disorder, and none were participating in any regular exercise program. All of the subjects engaged in the one-legged isokinetic exercise had previously used their right foot to kick a soccer ball. RMS Value Measure RMS voltage was recorded by an Excel b electromyography machine. Electrical activity was detected by means of two silver-silver chloride surface electrodes. Each surface electrode had a diameter of 9mm and was applied with a center-to-center distance of 20mm, placed parallel to the muscle fibers, and distal to the motor point. Before the electrodes were attached, the skin area was rubbed with alcohol. After surface electrodes had been applied, the impedance was checked and only values below 5kilo-ohms were permitted. The electrical signal was passed through a 2-channel mode amplifier (with notch filter function on) with a gain of 1 to 2mV per division, and the bandpass filter was set at 3 to 10,000Hz. The sweep speed was set at 10msec per division to analyze the RMS value per second. Procedure Test for relationship between RMS value and force. Exerted isometric force was measured with an Axis c muscle tester while the subjects were seated in an assembly seat of the Axis muscle tester. The back was supported, and hip and knee flexed at 90. Subjects were asked to perform three maximal voluntary contractions (MVC) lasting 3 to 5 seconds each, 3 minutes apart. The largest value of each trial was taken, and the MVC was defined as the mean value of three trials. After a resting period of 5 minutes, subjects were asked to contract at different force levels and to maintain a target level force shown on screen. Target forces were, in sequence, 20%, 40%, 60%, and 80% of MVC or in an inverse sequence. Each force level was maintained for 5 seconds. Between muscle contraction tasks at each level, 2-minute rest periods were allowed. After finishing a test for one site, subjects rested for 5 minutes. The RMS voltage was recorded for 1 second during which subjects showed the largest force of each trial, and the mean value of three trials was taken as the RMS value for MVC. The RMS value of each target force level was obtained by recording the RMS voltage over the 3 middle seconds of the 5-second stabilized contraction followed by a division by 3. The RMS and force values were normalized by the values obtained during maximal isometric contraction. One-legged isokinetic exercise test. The isokinetic exercise was done with the Cybex II+ machine a. Right knees were used for one-legged isokinetic exercise, and the contralateral stabilization bar, which is detachable, was positioned in front of, behind, and on both in front of and behind the opposite ankle joints above the malleoli (fig). We used the angular velocity with a speed of 90 /sec for testing to approximate each unidirectional exercising time to 1 second, because we set the Excel electromyography machine to analyze the RMS voltage per second. The isokinetic testing session consisted of three exercise conditions, five maximal isokinetic extensions, five maximal isokinetic flexions, and five maximal extension-flexion isokinetic exercises. An interval of 2 minutes was allowed between each exercise condition. The session was repeated at each bar position with a 5- minute rest interval. The testing order of bar position was randomized. Before testing, the RMS value for MVC was obtained from the vastus lateralis site and medial hamstring site by performing maximal isometric contraction of the left knee extensors and flexors with the hip and knee flexed at 90. In the case of knee extension or flexion exercise, the RMS voltage was recorded for 5 seconds. The minimum and maximum values were subtracted, and then the mean value of the remaining 3 seconds was adopted. The RMS voltage, which was recorded from the vastus lateralis site or the medial hamstring site during the last 6 seconds of the extension-flexion exercise, was averaged respectively. The mean RMS value for each condition was then computed as a percentage of the mean RMS value recorded from the same muscles during maximal contraction. DATA ANALYSIS The data were analyzed using an SPSS statistical program. Correlation coefficients were used for statistical analyses between normalized RMS value and force in vastus lateralis and medial hamstring sites. The means of normalized RMS values recorded from vastus lateralis and medial hamstring sites of unexercised legs were compared. The calculations between the different positions of the bar at each exercise condition were done by analysis of variance (one-way AN- OVA). RESULTS Table 1 shows significant correlation between RMS value and force, the correlation coefficients were 0.96 for the vastus lateralis site, and 0.95 for medial hamstring site. The RMS values recorded from the vastus lateralis sites of the unexercised legs (table 2) were not influenced by the position of bar (F = 1.83) during one-legged extension exercise. In contrast, the RMS values recorded from the medial hamstring sites of the unexercised leg (table 2) were significantly (p <.001) different (F = 37.25) among the three different bar positions. The amount of myoelectrical activity from the medial hamstring site seemed to be influenced by the position of the bar during isokinetic extension exercise of the opposite leg. Results from the isokinetic knee flexion exercise testing (table 3) indicated that significantly (p <.001) greater RMS values were recorded from the vastus lateralis sites when the bar was located in front of or on both sides of the unexercised leg (F = 58.09) (table 3). At medial hamstring sites, similar RMS voltages were recorded at the three different positions of the bar (F = 1.17) (table 3). During one-legged isokinetic extension-flexion exercise, the mean values of RMS voltage were greater (F = 38.75) when the bar was positioned in front of or on both sides of the opposite unexercised leg in the vastus lateralis site (table 4). At the medial hamstring site, greater value (F = 22.54) was noticed when the bar was located behind or on both sides (table 4). Arch Phys Med Rehabi! Vol 76, February 1995

3 MODIFIED CONTRALATERAL STABILIZATION BAR, Kang 179 The contralateral stabilization bar, which is detachable, was positioned (A) in front of, (B) behind, and (C) on both sides of the unexercised leg. DISCUSSION With respect to the effect of one-legged exercise on the strength of the contralateral leg, Panin and coworkers 7 observed in their study that the amount of electromyographic activity recorded from the contralateral antagonistic muscles was greater than the amount of electromyographic activity recorded from agonistic muscles. They explained that the reason is that electromyographic activity increased in these muscles as they were used to stabilize the body during exercise. Devine and colleagues ~ suggested that integrated electromyographic activities recorded during contralateral exertable 1: Normalized RMS Values at the Different Contraction Level Force Vastus Lateralis Site Medial Hamstring Site Level (n = 20) (n = 20) 20% M V C 40% M V C 60% M V C 8(1% M V C 100% M V C Correlation 17.3 Jr _ _+ lo.l 72.3 _ ± * 17.1 ± ± _ ± _ * Values are g i v e n as m e a n and SD (%). cise seemed to be related to the associated movement of the unexercised limb, and the muscles used to stabilize the body may depend on the position of the unexercised limb, the nature and extent of exercise, and which limb (upper or lower) was used in the study. 1'2'5'2~ Komi and coworkers 22noted that after 12 weeks of isometric strength training, isometric strength increased in the untrained leg as well as the trained leg, even though the amount Table 2: Normalized RMS Values of the Unexercised Muscles During Contralateral Knee Extension Exercise Vastus Lateralis Site Medial Hamstring Site Position of Bar (n = 27) (n = 27) Front Behind Both F value 8.0 ± ± ± t 58.5 ± 21.8 t 58.0 ± 16.1 t 37.25* Values are g i v e n as m e a n and SD (%). Position of bar is expressed as " F r o n t " w h e n the stabilization bar was located in front of the ankle joint, " B e h i n d " w h e n the stabilization bar was located behind the ankle joint, and " B o t h " when the stabilization bar was located on both in front of and b e h i n d the ankle joint of the unexercised leg. Statistically significant with multiple range test (LSD).

4 180 MODIFIED CONTRALATERAL STABILIZATION BAR, Kang Table 3: Normalized RMS Values of the Unexercised Muscles During Contralateral Knee Flexion Exercise Vastus Lateralis Site Medial Hamstring Site Position of Bar (n = 27) (n = 27) Front ' 9.7 _+ 6.2 Behind * Both t 12.3 _+ 7.3 F value 58.09* 1.17 Values are given as mean and SD (%). * Statistically significant with multiple range test (LSD). of increment was lesser in the untrained leg than the trained leg. Parker 6 trained the quadriceps femoris with isometric exercises for 4 months and obtained an increase in contralateral strength of 15%. In the study of Kang and colleagues, 23 they noticed that isokinetic one-legged exercise of a 6-week duration resulted in the increase of muscle strength in both the exercised leg and the unexercised leg. But in the unexercised leg, only the quadriceps showed a significant increment. It is assumed that the reason for a larger strength gain in the quadriceps of the unexercised leg is the effect of the contralateral stabilization bar, as well as the cross-educational effect. It is thought that the contralateral stabilization bar can load resistance on the extensors of the contralateral leg during one-legged isokinetic exercise. Kannus and coworkers 4 also reported the effects of one-legged isokinetic exercise for a 7-week period. In their results, quadriceps muscles received more benefits in the strength and power parameter, yet hamstring muscles received more benefits in the endurance parameter. The strength benefit of one-legged exercise to the opposite site can be obtained from the cross-educational effect as mentioned previously. 2-4'6'7'24 Despite a lack of well-argued scientific evidence of cross-educational effect, 4'24 some mechanisms about the rationale for cross-educational effect were suggested. Neurophysiologically, the secondary spindle reflex can cause a generalized diffuse regional response, and the cross extension-flexion reflex can lead to a reflex contraction of the muscles of the contralateral extremity. By this reflex mechanism, flexion of one hip or knee will decrease the flexor tone and increase the extensor tone in the muscles of the opposite extremity.25'26 Another multiextremity postural reflex that can influence the muscles of the unexercised limb is tonic neck reflex. This reflex is found in healthy subjects proportional to the intensity of effort, and used to facilitate the stronger muscular contractions. 3'zs Through these reflexes the exercise effect can be transferred to unexercised extremity. Other possible mechanisms for the cross-educational effect are a theory of neuromuscular facilitation22"27'28; and the central psychological effects of unilateral training. 27 To use electrical activity from the contracting muscle as a substitute measure of force rests on the assumption that myoelectrical signal-force relationships are linear and can be reliably measured. ~2'~6'29 The relationship between electrical activity and force or tension of contracting muscle is commonly thought to be linear, 1 '13A5'16"29 and some results of studies regarding electrical activity and force suggested that surface electrode recorded myoelectrical signals can be used as a substitute measure for force. 11"16"19 Basmajian and Deluca 3 recommended RMS values among the different methods for quantification of the electromyographic signal in the study of myoelectrical signal-force relationships. As mentioned earlier, Moritani and DeVreis 15 had warned against generalizing the findings obtained from a specific muscle to other muscles or other experimental conditions. In our study, before performing the test to investigate the effect of the position of the contralateral stabilization bar, we investigated the relationship between the force and the RMS value of the vastus medialis site and the medial hamstring site under isometric contraction from 0 to 100% of MVC. The results showed a linear relationship between the force exerted and the RMS value in those recording sites. On the basis of these results, we have conducted a study on the effect of the position of the bar on the unexercised knee muscles. Every RMS value has been normalized by the RMS value of the MVC of each condition to reduce individual variability and site variability in electrical activity./tm As intensity of effort increases from slow walking to running, the secondary sensory spindle reflex posture becomes more evident both in its long spinal and in its crossed extension-flexion components. 25 This induces motions to occur reciprocally, so almost every person tends to flex the contralateral knee joint during knee extension exercise. 24 As a result the bar can load resistance on the flexors of the unexercising leg when the bar is located behind or on both sides of the ankle joint by limiting the associated movement. On the basis of this rationale, isometric contraction of flexors of the unexercised leg may occur, thus we could record a significant high value of RMS voltage from the medial hamstring site of the unexercised leg. In the knee flexion exercise, the same results could be obtained from the vastus lateralis site of the unexercised leg when the bar was located in front of or on both sides of the ankle joint. To confirm the effect of the positioning of the bar once more, the myoelectrical signal was recorded during extension and flexion isokinetic exercise. The RMS voltage also showed high value at the vastus lateralis site when the bar was located in front of and on both sides of the ankle joint, and at the medial hamstring site behind and on both sides. But the recorded myoelectrical signal was lesser than that recorded during unidirectional exercise, because contralateral extensors or flexors may be contracted alternatively during extension-flexion isokinetic exercise. Table 4: Normalized RMS Values of the Unexercised Muscles During Contralateral Knee Extension-flexion Exercise Vastus Lateralis Site Medial Hamstring Site Position of Bar (n = 27) (n = 27) Front ' ' Behind * ' Both ' ' F value 38.75* 22.54* Values are given as mean and SD (%). * Statistically significant with multiple range test (LSD).

5 MODIFIED CONTRALATERAL STABILIZATION BAR, Kang 181 When the bar is located on both sides of the ankle joint, despite which muscles are being contracted by associated movement, resistance can be loaded on the contracting muscle by limiting the associated movement. In considering the interlimb effect related to strength, we must give attention to the bilateral deficit phenomenon. 24'26"32 When the bilateral homologous muscles are concurrently activated, there is a decrement in the strength of each limb by a neural mechanism known as a bilateral deficit. 24'26'27"33 We tend to use our legs more often in a reciprocal manner in ordinary activities a:ad exercise than in a concurrent mode like vertical jumping. ~ It would be difficult to confirm without exact analysis of the exercise motion, but some subjects tend to rely on the unexercising leg on the bar when the bar is located at only one side with progressing exercise, even though they exercise their legs in a reciprocal manner at the beginning of an exercise. Theoretically, a decrement in the strength may occur because of a bilateral deficit, except in subjects specially trained for a concurrent mode, with such a simultaneous activation of bilateral homologous muscle in a part of exercise. 32'33 Thus, we thought it would be helpful to induce reciprocal motions to increase the effect of exercise, and such a reciprocal motion may be more easily obtained by locating the bar on both sides of the unexercised leg. In summary, the subject will feel more stability and receive a better exercise effect on the unexercised leg during one-legged isokinetic exercise when the bar is located on both sides of the opposite leg. The bar located on both sides can provoke isometric contraction of the muscles of the unexercised leg by limiting the associated movement. Finally, in this study, we used the stabilization bar as shown in the figure to understand the effect of the bar on the unexercised leg. In practical use, we can acquire such ~tn effect simply by attaching a shin pad with a strap to the unexercised leg. Moreover, we suggest a further modified stabilization bar that has the shin pad with strap, and can change the application angle. Because each group of muscles has the joint angle where the contracting muscle has an optimal mechanical advantage that the muscle has developed maximal tension, 34'35 and the isometric strength is mainly specific according to the angles at which the knee was exercised. It is suggested that isometric exercise would preferably be performed at different angles to secure an optimal total strength increase Thus, the stabilization bar that can change the application angle is more practical and useful and can be applicable for the patient with a contracted knee joint. References 1. Devine KL, LeVeau BF, Yacy HJ. Electromyographic activity recorded from an unexercised muscle during maximal isometric exercise of the contralateral agonists and antagonists. Phys Ther 1981;61: Gregg RA, Mastellone AF, Gersten JW. Cross exercise: a review of the literature and study utilizing electromyographic techniques. Am J Phys Med 1957;36: Hellebrandt FA, Parrish AM, Houtz SJ. Cross education: the influence of unilateral exercise on the contralateral limb. Arch Phys Med Rehabil 1947; 28: Kannus P, Alosa D, Cook L, Johnson R J, Renstrom P, Pope M, et al. Effect of one-legged exercise on the strength, power and endurance of the contralateral leg: a randomized, controlled study using isometric and concentric isokinetic training. Eur J Appl Physiol 1992;64: Moore JC. Excitation overflow: an electromyographic investigation. Arch Phys Med Rehabil 1975;56: Parker RH. The effects of mild one-legged isometric or dynamic training. Eur J Appl Physiol 1985;54: Panin N, Lindenauer HJ, Weiss AA, Ebel A. Electromyographic evaluation of the 'cross exercise' effect. Arch Phys Med Rehabil 1961 ;42: Rutherford OM, Jones DA. The role of learning and coordination in strength training. Eur J Appl Physiol 1986; 55: DeLuca CJ, Van Dyke EJ. Derivation of some parameters of myoelectric signals recorded during sustained constant force isometric contractions. Biophys J 1975; 15: Edwards RG, Lippold OCJ. The relation between force and integrated electrical activity in fatigued muscles. J Physiol 1956; 132: I. Fiebert IM, LeBlanc WG, McGuane SA, Schnoes CD, Strickland KM. The relationship of electromyographic activity and force of the vastus medialis oblique and vastus lateralis muscles during maximal isometric knee extension contractions. Isokinetics Exerc Sci 1992;2: Lawrence JH, DeLuca CJ. Myoelectric signal versus force relationship in different human muscles. J Appl Physiol 1983;54(6): Lippold OCJ. The relation between integrated action potentials in a human muscle and its isometric tension. J Physiol (Lond) 1952; 117: Milner-Brown HS, Stein RB. The relation between the surface electromyogram and muscular force. J Physiol (Lond) 1975;246: Moritani T, DeVries HA. Reexamination of the relationship between the surface integrated electromyogram (IEMG) and force of isometric contraction. Am J Phys Med Rehabil 1978;57: Philipson L, Larson PG. The electriomyographic signal as a measure of muscular force and comparison of detection and quantification techniques. Electromyogr Clin Neurophysiol 1988; 28: DeLuca CJ. Physiology and mathematics of myoelectric signals. IEEE Trans Biomed Eng 1979;26: DeLuca CJ. Myoelectrical manifestations of localized muscular fatigue in humans. Crit Rev Biomed Eng 1985; 11: Moritani T, Muro M. Motor unit activity and surface electromyogram power spectrum during increasing force of contraction. Eur J Appl Physiol 1987;56: Veiersted KB. The reproducibility of test contractions for calibration of electromyographic measurements. Eur J Appl Physiol 1991; 62: Hellebrandt FA, Waterland JC. Expansion of motor patterning under exercise stress. Am J Phys Med 1962;41: Komi PV, Viitasalo JT, Rauramaa R, Vihko V. Effect of isometric strength training on mechanical, electrical, and metabolic aspects of muscle function. Eur J Appl Physiol 1978;40: Kang SW, Moon JH, Cho KJ, Shin JS. Effects of 2 speeds of isokinetic training on muscular strength in quadriceps and hamstrings. J Korean Acad Rehabil Med 1991; 15:77-88(Kor) 24. Enoka RM. Muscle strength and its development: new perspectives. Sports Med 1988;6: Kottke FJ. The neurophysiology of motor function. In: Kottke FJ, Lehmann JF, editors. Krusen's handbook of physical medicine and rehabilitation, 4th ed. Philadelphia: Saunders, 1990: Vandervoort AA, Sale DG, Moroz JR. Comparison of motor unit activation during unilateral and bilateral leg extension. J Appl Physiol 1984;56: Coyle EF, Feiring DC, Rotkis TC, Cote RW, Roby FB. Specificity of power improvements through slow and fast isokinetic training. J Appl Physiol 1981 ;51: Hakkinen K. Neuromuscular and hormonal adaptation during strength and power training. A review. J Sports Med Phys Fitness 1989;29: Weir JP, Wagner LL, Housh TJ. Linearity and reliability of the IEMG v torque relationship for the forearm flexors and leg extensors. Am J Phys Med Rehabil 1992;71: Basmajian JV, Deluca CJ. Description and analysis of EMG signal. In: Basmajian JV, Deluca CJ, editors. Muscles alive, 5th ed. Baltimore, London, Sydney: Williams & Wilkins, 1985:

6 182 MODIFIED CONTRALATERAL STABILIZATION BAR, Kang 31. Fridlund AJ, Cacioppo AJT. Guidelines for human electromyographic research. Psychophysiology 1986;23: Vandervoort AA, Sale DG, Moroz JR. Strength-velocity relationship and fatigability of unilateral versus bilateral ann extension. Eur J Appl Physiol 1987;56: Sechcr NH, Rorsgaard S, Secher O. Contralateral influence on recruitment of curarized muscle fibers during maximal voluntary extension of the legs. Acta Physiol Scand 1978; 103: Baltzopoulos V, Brodie DA. Isokinetic dynamometer, applications and limitations. Sports Med 1989;8:101-16, 35. Coyle E, Costill D, Lesmes G. Leg extension power and muscle fiber composition. Med Sci Sports 1979; 11 : Kitai TA, Sale DG. Specificity of joint angle in isometric training. Eur J Appl Physiol 1989;58: Knapik JJ, Roberta H, Mawdsley, Marcos U, Ramos MU. Angular specificity and test mode specificity of isometric and isokinetic strength training. J Orthop Sports Phys Ther 1983;5: Lindh M. Increase of muscle strength from isometric quadriceps exercises at different knee angles. Scand J Rehabil Med 1979; 11:33-6. Suppliers a. Cybex, Division of Lumex, Incorporated, 2100 Smithtown Avenue, PO Box 9003, Ronkonkoma, NY b. Cadwell Laboratories Incorporated, 909 North Kellogg Street, Kennewick, WA c. FARO Medical Technologies Incorporated, 125 Technology Park, Lake Murray, FL