Electromyographic Activity Recorded from an Unexercised Muscle During Maximal Isometric Exercise of the Contralateral Agonists and Antagonists

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1 Electromyographic Activity Recorded from an Unexercised Muscle During Maximal Isometric Exercise of the Contralateral Agonists and Antagonists KATHLEEN L. DEVINE, MS, BARNEY F. LeVEAU, PhD, and H. JOHN YACK, BS The purpose of this study was to determine if integrated electromyographic activity recorded from an unexercised muscle during contralateral exercise was dependent upon the contralateral muscle (agonist or antagonist) being exercised and upon the position of the unexercised limb. Twenty normal subjects participated in the study. Electromyographic activity was recorded, using surface electrodes, from the right rectus femoris and the right vastus lateralis muscles during four experimental conditions. Statistical analysis revealed that ) integrated electromyographic activity recorded from the rectus femoris muscle during contralateral, isometric exercise was not significantly influenced by the position of the unexercised knee or the exercised contralateral muscle and ) integrated electromyographic activity recorded from the vastus lateralis muscle during contralateral, isometric exercise was significantly greater when the unexercised knee was initially positioned in 0 degrees of flexion and the contralateral agonists were exercised. Integrated electromyographic activity recorded during contralateral exercise appeared to be related to the associated movements of the unexercised limb. Key Words: Muscle contraction, Posture, Neural transmission, Electromyography. Patients who cannot actively exercise a limb or who have nonfunctioning innervated muscles may benefit from contralateral exercise ("cross-exercise"). The benefits of contralateral exercise may include decreased muscle atrophy, maintenance of motor coordination, and increased muscle strength of the affected limb. A better understanding of the effects of specified cross-exercise procedures will allow a therapist to provide improved treatment and rehabilitation of patients with neuromuscular disease and orthopedic problems. Researchers have used EMG to show that muscles can be activated by contralateral exercise. " 5 The comparative effects of exercising the agonistic and antagonistic muscles require further definition. In addition, the effect of limb position on the distribution of EMG Mrs. Devine was a graduate student at the University of North Carolina, Chapel Hill, NC, when this study was conducted. She is now Assistant Professor, Department of Physical Therapy, University of Illinois, SW Glendale Ave, PO Box 649, Peoria, IL 6656 (USA). Dr. LeVeau is Associate Professor, Department of Physical Therapy, University of North Carolina, Chapel Hill, NC 754. Mr. Yack is Research Assistant, Department of Physical Therapy, University of North Carolina, Chapel Hill. This article was submitted December, 979, and accepted October 0, 980. activity has not been elucidated. The purpose of this study was to determine if integrated electromyographic (IEMG) activity recorded from an unexercised muscle during contralateral exercise is dependent upon which contralateral muscle (agonist or antagonist) is being exercised and the position of the unexercised limb. Researchers have observed EMG activity in an unexercised limb concomitant with exercise of a different limb. -5 The nature and extent of the exercise needed to produce EMG activity in an unexercised contralateral limb are controversial. Gregg and associates did not record any EMG activity from unexercised triceps brachii and biceps brachii muscles during maximal isometric exercise and nonresisted isotonic exercise of the contralateral muscles that flex the elbow. 4 They did record EMG activity, however, from both unexercised muscles as resistance was applied during isotonic exercise of the contralateral elbow flexor muscles. Similarly, Sills and Olson reported an increase in EMG activity recorded from an unexercised muscle during an increase in the amount of resistance applied to isotonic exercise of the contralateral limb. Conversely, Moore observed EMG activity in an unexercised muscle during isometric 898 PHYSICAL THERAPY

2 exercise of the contralateral limb, but did not find an increase in EMG activity recorded from an unexer cised muscle during increased resistance to the exer cised contralateral limb.5 Two groups of authors compared the EMG activity recorded from the contralateral, unexercised agonistic and antagonistic muscle groups. These authors re ported that the amount of EMG activity recorded from the contralateral, antagonistic muscles was greater than the amount of EMG activity recorded from the contralateral, agonistic muscles during re sisted isotonic exercise., 4 Panin and associates sug gested that EMG activity increased in those muscles used to stabilize the body while exercise was being performed. The muscles used to stabilize the body may depend upon the position of the unexercised limb. Gregg and associates indicated that, for the upper limb, the position of the unexercised limb did not influence the amount of EMG activity recorded from an unexer cised muscle.4 These results, however, may not hold true for the lower limb. Postural movements of an unexercised limb from the initially set position during contralateral exercise may affect the EMG activity recorded from the unex ercised muscles. Two groups of researchers indicated that postural adjustments were associated with heavy resistive exercise and proposed that cross-exercise was dependent upon these postural adjustments.6, 7 Hellebrandt and Waterland reported that the type of associated movements concomitant with heavy resis tive exercise was consistent for each subject but varied among subjects.7 One author proposed that these associated movements increased or maintained the stability of the body.8 We proposed two hypotheses based on the preced ing review of literature. First, the IEMG activity recorded from the rectus femoris and vastus lateralis muscles during maximal, isometric exercise of the contralateral hamstring muscles is significantly greater than the IEMG activity recorded during max imal, isometric exercise of the contralateral quadri ceps femoris muscles. Second, the IEMG activity recorded from the rectus femoris and vastus lateralis muscles during maximal, isometric exercise of the contralateral quadriceps femoris and hamstring mus cle groups is not significantly influenced by the po sition of the unexercised limb. Fig.. Positioning for exercise conditions with right knee flexed approximately 90 degrees. Subjects participated in the study on two consecu tive days. The purpose of the first session was to obtain maximal, isometric torque values for the left knee flexor muscles and the left and right knee exten sor muscles, using a Cybex II dynamometer.* Each subject was seated and provided with a backrest to maintain the hip angle at 70 degrees of flexion.9, 0 A thigh strap was positioned over the anterior thigh proximal to the patella to stabilize the exercising leg. Subjects were instructed to grasp the seat parallel to * Cybex, Division of Lumex, Inc, 00 Smithtown Ave, Ronkonkoma, NY 779. METHOD Our subjects were 0 normal volunteers, 6 men and 4 women, between and years old. Each subject was right-handed; had normal, healthy knee joints and surrounding musculature; and had no complaint of pain in the low back or lower limbs. Volume 6 / Number 6, June 98 Fig.. Positioning for exercise conditions with right knee flexed 0 degrees. 899

3 Group TABLE Sequence of Exercise Group s Group, the hip joints to help stabilize the trunk (Fig. I). Maximal isometric torque values were determined for left and right knee extension with the knee flexed to 60 degrees and left knee flexion with the knee flexed to 50 degrees. Subjects were instructed by a taperecorded voice to perform a maximal isometric contraction and to sustain this contraction for five seconds. An interval of two and one-half minutes was allowed between contractions. 4 Before the next isometric contraction, the level of torque produced during the previous contraction was displayed on an oscilloscope. Each subject was instructed to obtain a torque level above the level displayed with the next contraction. Subjects performed isometric contractions until an increase in torque output could no longer be produced. The highest level of torque output sustained for five seconds was labeled as the maximal isometric torque. On the second day of the study (4 ± hours after the first day), IEMG activity was recorded from the right rectus femoris and vastus lateralis muscles using Beckman biopotential 6-mm silver-silver chloride surface electrodes. 5 Skin resistance was reduced to below 0 kω by abrading the skin, using the skindrilling technique described by Shackel. 6 Electrodes were positioned parallel to the muscle fibers on the right rectus femoris muscle, one-half the distance between the anterior superior iliac spine and the superior pole of the patella and on the right vastus lateralis muscle, one-half the distance between the greater trochanter and the lateral superior pole of the patella. The distance between the centers of the electrodes was cm. Total integration of the raw EMG signal was processed at half-second intervals by EMG equipment with a frequency response of between 0 Hz and 0,000 Hz. Both the raw and the IEMG signals were channeled through a Honeywell Visicorder and recorded on ultraviolet light-sensitive paper. Integrated EMG activity was recorded during four exercise conditions. The level of maximal torque output recorded the preceding day was displayed on an oscilloscope directly in front of the seated subject. Each subject was instructed by a tape-recorded voice to match this displayed level of torque with each contraction. Subjects were assigned to one of three groups in which the sequence of the following exercise conditions was varied: ) a maximal isometric contraction of the muscles that extend the left knee, with the right knee initially positioned in about 90 degrees of flexion (), ) a maximal isometric contraction of the muscles that extend the left knee, with the right knee initially positioned in 0 degrees of flexion () (Fig. ), ) a maximal isometric contraction of the muscles that flex the left knee, with the right knee initially positioned in about 90 degrees of flexion (), and 4) a maximal isometric contraction of the muscles that flex the left knee, with the right knee initially positioned in 0 degrees of flexion (). Each sequence of exercise conditions allowed for alternate contractions of the left quadriceps femoris and hamstring muscle groups (Tab. ). An-interval of two and one-half minutes was allowed between exercise conditions. Two trials for each exercise condition were performed. Beckman Instruments, Inc, 900 River Rd, Schiller Park, IL Honeywell Corp, 500 Evans Ave, Denver, CO 807. TABLE Electrical Activity Recorded from Tested Muscles Computed as a Percentage of the Electrical Activity During a Maximal Isometric Contraction Left knee extended, right knee flexed () Left knee extended, right knee extended () Left knee flexed, right knee flexed () 4 Left knee flexed, right knee extended () a Significantly different from the other three means at the.0 level. Rectus Femoris X ±s (%) 8.5 ± ± ± 6.0. ± 9. Vastus Lateralis + s (%) 6. ± ± 47. a 9.4 ± ± 0. Recorded 900 PHYSICAL THERAPY

4 Source of Variation Among groups Exercised muscle Position of right knee Error a Significant at the.0 level. TABLE Analysis of Variance for Vastus Lateralis: Percentages of Maximum df 76 SS,84.4,8.6,6.5 50, MS 0,947.4,8.6, F 6.4 a 9.9 a 8.5 a For each subject, the IEMG activity that was recorded from the right rectus femoris and the right vastus lateralis muscles during the last three seconds of each five-second isometric contraction was averaged for each condition. This three-second time interval was selected for analysis to allow subjects to obtain maximal torque. The mean IEMG activity for each condition was then computed as a percentage of the mean IEMG activity recorded from the same muscles during a five-second maximal isometric contraction of the right knee extensor muscles with the knee flexed to 60 degrees. A two-times-two factorial analysis of variance was performed on each group of percentages, and significance was determined at the.0 level. If an F value was found to be significant, a Duncan's new multiple-range test was used to compare the means. Movements of the right lower extremity, trunk, and head concomitant with maximal isometric contractions of the left knee flexor and extensor muscles were recorded on a Video Instant Playback System,** using split-screen taping. One camera was focused on the right lower extremity and the second camera was focused on the trunk and head. The type of associated movements of the right hip and knee, trunk, and head were determined by one investigator, who viewed the videotape after the experiment was completed. RESULTS The amount of IEMG activity recorded from the rectus femoris muscle (Tab. ) was not influenced by the contralateral muscle group being exercised (F =.09) or the position of the unexercised limb (F = 0.6). No significant difference (F =.5) was found among the four exercise conditions. ** Redlake Corp, 99 Corwin Dr, Santa Clara, CA In contrast, the IEMG activity recorded from the vastus lateralis muscle (Tab. ) was significantly (p <.0) different (F = 6.4) among the four exercise conditions (Tab. ). The percentages of IEMG activity from this muscle appeared to be influenced by the contralateral muscle being exercised (F = 9.9) and by the position of the unexercised limb (F = 8.5). Mean percentages of IEMG activity were greater when the contralateral agonistic muscle was exercised and the unexercised knee was initially positioned in 0 degrees of flexion. Results from the Duncan's new multiple-range test (Tab. 4) indicated that significantly (p <.0) greater IEMG activity was recorded from the vastus lateralis muscle during condition two (). No significant difference in IEMG activity was found among the other three exercise conditions. Associated movements of the right hip and knee have been summarized in Tables 5 and 6. The most frequent associated movements of the right lower extremity were hip extension and knee flexion during condition one, hip and knee extension during condition two, and hip and knee flexion during conditions three and four. Although associated movements of the trunk and head were consistent between the two trials of each condition for each subject, there was no apparent pattern of associated movements of the trunk and head among the subjects. DISCUSSION Whether IEMG activity recorded from an unexercised muscle during contralateral exercise is influenced by the contralateral muscle's being exercised and the position of the unexercised limb appears to depend upon the unexercised muscle. Results of this study support the findings of Moore that EMG activity can be recorded from an unexercised limb during isometric exercise of the contralateral limb. 5 The per- TABLE 4 Results of Duncan's New Multiple-Range Test: Comparison of the Mean Values Recorded from Vastus Lateralis Muscle Mean: Percent Maximum a Significantly different from the other three means at the.0 level a Volume 6 / Number 6, June 98 90

5 TABLE 5 Number of Subjects with Associated Movements of the Right Hip 4 Flexion 7 8 Extension 5 4 No Visible Movement centages of IEMG activity recorded from the unexercised rectus femoris muscle in the four exercise conditions (8.5% to.9%) and the percentages of IEMG activity recorded from the unexercised vastus lateralis muscle in three exercise conditions (9.4% to 6.%) are similar to the 0 to 0 percent reported by Moore. Our findings on the rectus femoris muscle are also similar to the results of Panin and associates, who reported that none of the unexercised muscles reached more than 0 percent of the exercised muscles. In contrast, one exercise condition for the vastus lateralis muscle was significantly greater than 0 percent. Both Moore and Panin and associates compared the EMG activity recorded from the unexercised muscles with maximal EMG values recorded from the exercised muscles., 5 We compared the IEMG values from the unexercised muscles during contralateral exercise with IEMG values recorded from the same muscles during a maximal isometric contraction. Moore stated that the 0- to 0-percent EMG values could have some exercise effect "for maintaining a degree of muscle tone and tissue turgor in a limb that is temporarily immobilized." 5 Panin and associates, however, considered the EMG values of 0 percent and below of insufficient magnitude to constitute an exercise effect. The exercise effect for three of the four exercise conditions for the vastus lateralis muscle may be questionable, but the 60- percent value recorded during exercise condition two is well above the percentage level Panin and associates considered necessary for an exercise effect. Two research teams reported that EMG activity recorded from the contralateral antagonists was greater than the EMG activity recorded from the contralateral agonist., 4 Conversely, our study indicated that the contralateral agonist and not the con- TABLE 6 Number of Subjects with Associated Movements of the Right Knee 4 Flexion Extension No Visible Movement 0 4 tralateral antagonist produced the greater IEMG activity. The differences in our results may be related to ) the use of the upper limb in one study 4 and ) the testing position of the unexercised lower limb in the other study. Gregg and associates studied EMG activity recorded from muscles in the upper limb. 4 Our results were obtained from muscles in the lower limb. Muscles of the upper limb may respond differently to contralateral exercise than do muscles of the lower limb. Subjects in the study reported by Panin and associates were positioned supine with the unexercised knee in full extension. In contrast, subjects in our study were positioned sitting with the unexercised knee either in 0 degrees or 90 degrees of flexion. Gregg and associates stated that the position of the unexercised limb did not influence the appearance of EMG activity. 4 In our study, however, the position of the unexercised limb did influence the amount of IEMG activity recorded from the vastus lateralis muscle. This difference in results may be related to the movements of the unexercised limb during contralateral exercise that were observed in our study and were not reported by Gregg and associates. The IEMG activity recorded from both the rectus femoris and vastus lateralis muscles appeared to be related to the associated movements of the right hip and knee. Integrated EMG activity recorded from the rectus femoris muscle was not significantly different among the four exercise conditions, probably because this muscle helped to produce flexion of the hip and extension of the knee. Different combinations of associated flexion of the hip and extension of the knee occurred during all four exercise conditions. Conversely, IEMG activity recorded from the vastus lateralis muscle during contralateral exercise was significantly different for exercise condition two (), which was the only exercise condition in which associated knee extension primarily occurred. The most prevalent associated movement of the right knee during the other three exercise conditions was flexion. During the two exercise conditions in which the right knee was initially positioned in flexion, associated knee flexion was probably used to increase the stability of the subject by providing an additional force between the calf of the subject and the seat. Increased stability was apparently needed with a contraction of both the contralateral agonists and antagonists. An explanation of the results of the conditions in which the right knee was initially positioned in 0 degrees of flexion is less clear. The motion of the right unexercised knee paralleled the attempted motion of the left exercised knee. This associated motion may also be related to stabilization of the body. Maximal isometric contractions of the left knee flexor and extensor muscles appeared to produce a rota- 90 PHYSICAL THERAPY

6 tional force in the direction of the muscle contraction. A counterrotational force produced by the same knee motion on the contralateral side would help stabilize the body. The lack of consistent associated movements of the trunk and head among subjects supports the observations made by Hellebrandt and Waterland. 7 A lesser variety of associated trunk movements appears to be related to the stabilization of the trunk by the upper limb position. Physical therapists interested in producing the greatest EMG activity in an unexercised muscle during contralateral resistive exercise must determine the position in which the unexercised limb will be used to help stabilize the body. The results of this study indicate that specific exercise conditions provide different amounts of IEMG in the unexercised muscles. Our results also indicate the possibility of producing a large enough amount of IEMG activity in an unexercised muscle to constitute an exercise effect. More studies are needed ) to help the physical therapist determine the most effective exercise program that will produce EMG activity in an unexercised muscle, ) to determine the relationship between associated movements of an unexercised limb and stabilization of the body during maximal isometric exercise of the contralateral limb, and ) to determine the relationship between the amount of EMG activity in an unexercised muscle and the maintenance of muscle strength and motor coordination. CONCLUSIONS Four conclusions can be drawn from our results. First, in the lower limb, IEMG activity is produced in unexercised muscles during maximal isometric exercise of the contralateral limb. Second, the IEMG activity recorded from the rectus femoris muscle during maximal isometric exercise of the contralateral agonists and antagonists is not influenced by the position of either the unexercised knee or the exercised contralateral muscle. Third, an exercise effect can be produced in the vastus lateralis muscle during maximal, isometric exercise of the contralateral agonists when the unexercised knee is initially flexed 0 degrees. Fourth, the IEMG activity recorded from an unexercised muscle during contralateral exercise appears to be related to the associated movements of the unexercised limb. REFERENCES. Gellhorn E: Patterns of muscular activity in man. Arch Phys Med 8: , 947. Panin N, Lindenauer HJ, Weiss AA, et al: Electromyographic evaluation of "cross exercise" effect. Arch Phys Med Rehabil 4:47-5, 96. Sills FD, Olson AL: Action potentials in unexercised arm when opposite arm is exercised. Res Q 9:-, Gregg RA, Mastellone AF, Gersten JW: Cross exercise: A review of the literature and study utilizing electromyographic techniques. Am J Phys Med 6:69-80, Moore JC: Excitation overflow: An electromyographic investigation. Arch Phys Med Rehabil 56:5-0, Hellebrandt FA, Houtz SJ, Parrish AM: Cross education: The influence of unilateral exercise on the contralateral limb. Arch Phys Med 8:76-85, Hellebrandt FA, Waterland JC: Expansion of motor patterning under exercise stress. Am J Phys Med 4:56-66, Martin JP: The Basal Ganglia and Posture. Philadelphia, PA, J. B. Lippincott Co, 967, pp Currier DP: Positioning for the knee strengthening exercises. Phys Ther 57:48-5, 977 0: Richard G, Currier DP: Back stabilization during knee strengthening exercise. Phys Ther 57:0-05, 977. Clarke HH, Elkins EC, Martin GM, et al: Relationship between body position and the application of muscle power to movements of the joints. Arch Phys Med :8-89, 950. Mendler HM: Effect of stabilization on maximum isometric knee extensor force. Phys Ther 47:75-79, 967. Williams M, Stutzman L: Strength variation through the range of joint motion. Phys Ther Rev 8:67-675, Moore JC: Facilitation of forearm flexor response. J Appl Physiol : , Bouisset S, Maton B: Quantitative relationship between surface EMG and intramuscular electromyographic activity in voluntary movement. Am J Phys Med 5:85-95, Shackel B: Skin-drilling: A method of diminishing galvanic skin-potentials. Am J Psychol 7:4-, 959 Volume 6 / Number 6, June 98 90