Electromyographic Analysis of Knee Exercises in - Physical Therapy
Transcript of Electromyographic Analysis of Knee Exercises in - Physical Therapy
Electromyographic Analysis of Knee Exercises in Healthy Subjects and in Patients with Knee Pathologies
GARY L. SODERBERG, SCOTT DUESTERHAUS MINOR, KEVIN ARNOLD, THOMAS HENRY, JOYCE KIRCHNER CHATTERSON, DEBRA RIDENOUR POPPE, and CHERYL WALL
Little information exists about the intensity of contraction required from knee and hip musculature during common therapeutic exercises used for patient populations. This study, therefore, was designed to compare electromyographic data obtained from the vastus medialis, rectus femoris, gluteus medius, and biceps femoris muscles during maximally resisted straight-leg-raising (SLR) exercises with EMG data obtained from the same muscles during quadriceps femoris muscle setting (QS) exercises in healthy subjects and in patients with knee pathologies. Of the 30 participants in the study, 16 had a history of knee injury or surgery. All participants performed randomly ordered trials of the SLR and QS exercises while the EMG data were recorded from surface electrodes and normalized to values derived from maximal effort isometric contraction trials. An analysis of variance demonstrated significantly greater activity (p < .05) of the vastus medialis, biceps femoris, and gluteus medius muscles during QS exercises than during SLR exercises. The rectus femoris muscle was significantly more active (p < .05) during SLR exercises than during QS exercises. The study demonstrated remarkably different degrees of muscle activation between the SLR and QS exercises, indicating that the exercise selected will affect the therapeutic intention. Key Words: Biomechanics, Eiectromyography, Physical therapy.
In many treatment situations for knee injuries and pathologies, physical therapists use either straight-leg-raising (SLR) or quadriceps femoris muscle set
ting (QS) exercises, or both, for the purpose of improving a patient's ability to generate quadriceps femoris muscle tension. Little, however, is known about the effects of these two exercises on the intensity of muscular contraction required. Early work by Pocock led to the remark that relatively large amounts of electromyographic data were recorded from the quadriceps femoris muscles during the QS exercises, presumably because the muscle then was at its shortest length.1 In a 1966 study, Allington et al evaluated EMG recordings from 25 subjects who had completed a series of exercises.2 Maximal, manually resisted isometric contractions of the quadriceps femoris muscle were performed while the thigh was supported posteriorly. The position of the body was not specified. This type of contraction produced the highest EMG voltages in 67 of 75 tests. Voltages were greatest during the QS exercises in only 8 of 75 trials.
Gough and Ladley followed with a study of EMG recordings from the rectus femoris, vastus lateralis, and vastus medialis muscles during SLR and iso
metric contractions.3 Their data revealed that quadriceps femoris muscle activity was greater during isometric contraction in 25 subjects, as opposed to only 6 subjects for the SLR contraction. No details were provided as to how electrical activity from specific muscles related to these exercises.
More recently, Skurja et al reported on 20 subjects who completed both the SLR and QS exercises.4 Measurements included EMG data from the rectus femoris and the vastus medialis oblique muscles. Results showed that greater myoelectric activity was produced in the vasti muscles during isolated isometric knee extension than during the SLR exercises. The opposite was true for the EMG data obtained from the rectus femoris muscle. These findings were confirmed further in an extensive study by Soderberg and Cook in a sample of 40 healthy subjects.5 In their work, highly significant (p < .0001) differences existed in the EMG data between the SLR and QS exercises. Of the vastus medialis, biceps femoris, gluteus medius, and rectus femoris muscles, only the rectus fe-
Dr. Soderberg is Professor and Director, Physical Therapy Program, College of Medicine, The University of Iowa, Iowa City, IA 52242 (USA).
Dr. Minor is Assistant Professor, Department of Physical Therapy, College of Allied Medical Professions, University of Kentucky, Lexington, KY 40536-0084.
Mr. Arnold is a staff physical therapist, Mercy Hospital Medical Center, Sixth and University Ave, Des Moines, IA 50314.
Mr. Henry is a staff physical therapist, Michiana Rehabilitation Institute, Memorial Hospital of South Bend, 615 N Michigan St, South Bend, IN 46601.
Mrs. Chatterson is a staff physical therapist, Humana Hospital-Sunrise, PO Box 14157, Las Vegas, NV 89114.
Mrs. Poppe is a staff physical therapist, Mary Greeley Medical Center, 117 11th St, Ames, IA 50010.
Miss Wall is a senior physical therapist, Rehabilitation Unit, Saint Joseph's Hospital, 611 St. Joseph Ave, Marshfield, WI 54449.
Dr. Minor, Mr. Arnold, Mr. Henry, Mrs. Chatterson, Mrs. Poppe, and Miss Wall were students in the Physical Therapy Program, The University of Iowa, at the time the study was conducted.
This article was submitted September 3, 1986; was with the authors for revision five weeks; and was accepted March 3, 1987. Potential Conflict of Interest: 5.
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moris muscle was more active during the SLR exercises.
Few studies have included a patient population, and none have specifically evaluated a patient's response to the exercises investigated in this study. Stratford established, however, that patients with effused knees diminished myoelectric activity at 0 degrees when compared with the 30-degree flexed position.6 A year later, Krebs and associates evaluated 30 healthy and 18 postarthrotomy patients during SLR and QS exercises and found highly significant interaction of position (exercises) and limb condition (operated vs nonoperated).7
Although SLR and QS exercises have been used in other studies, they have been used in considerations associated with the effect of the exercise on patellar pain or patellar pain syndromes.8-10
Other studies, among them that of Lieb and Perry,11 have attempted to determine the specific role of the vastus medialis muscle in terminal knee extension. For a list of references and a discussion of this issue, the reader is referred to the 1981 work by Duarte-Cintra and Furlani.12
Frequent clinical use of QS and SLR exercises requires that physical therapists be knowledgeable about their effects. Previous work on healthy subjects has led us to hypothesize that patients would have greater rectus femoris muscle activity during the SLR exercises than during QS exercises. The converse should be true for the vastus medialis, gluteus medius, and biceps femoris muscles. Thus, the purpose of this study was to compare EMG data obtained from the vastus medialis, rectus femoris, gluteus medius, and biceps femoris muscles during maximally resisted SLR exercises with EMG data obtained from the same muscles during QS exercises in healthy subjects and in patients with knee pathologies.
METHOD
Subjects Thirty individuals participated in this
study. Fourteen were healthy subjects free from pathology, and 16 were patients (8 men, 8 women) who had a history of knee injury or surgery. All signed informed consent forms for the protocol that had been approved by The University of Iowa Committee on Human Subjects. Descriptive information on the two groups is shown in Table 1. All of the patients, whose status is shown in Table 2, had received or were receiv-
TABLE 1 Descriptive Characteristics of Subjects
Group
Healthy subjects (n = 14) Range
s Patients with knee pathologies
(n = 16) Range
s
Age (yr)
21-26 23.3 1.4
18-72 32.8 18.8
Height (m)
1.6-1.9 (5.2-6.2 ft) 1.7 (5.6 ft) 0.09 (0.3 ft)
1.6-1.9 (5.2-6.2 ft) 1.8 (5.9 ft) 0.1 (0.33 ft)
Weight (kg)
54-91.8 (119-202 lb) 68.6(151 lb) 13.7 (30.2 lb)
57.7-86.4 (127-190 lb) 70.8 (156 lb) 10.0 (22 lb)
TABLE 2 Description of Patient Pathology
Condition
Arthroscopy with meniscectomy of medial and lateral meniscus
Arthroscopy with lateral release Patellectomy with accompanying synovitis Medial collateral ligament sprain with subsequent
immobilization Total knee replacement secondary to degenerative joint
disease Undiagnosed knee pain, stiffness secondary to immobilization Meniscectomy with anterior cruciate ligament deficiency Arthrotomy with lateral release secondary to adhesion Anterior cruciate ligament repair and meniscus tear Intramedullary femoral rod and immobilization Allograft replacement of medial femoral condyle Lateral release and dovetail of tibial tubercle
Number of Patients
1 1 1
1
4 1 1 1 2 1 1 1
ing physical therapy at The University of Iowa Hospitals and Clinics or in the sports physical therapy facility in the athletic department at the time of testing. The mean length of time after injury or surgery was six weeks. All patients could generate sufficient quadriceps femoris muscle tension to maintain knee extension during the SLR exercises. The right knees of 10 healthy subjects and 9 patients were tested; the left knees of 4 healthy subjects and 7 patients were tested.
Preparation To record the myoelectric activity, the
skin of the tested knee was wiped with alcohol-soaked gauze. An electrode assembly* then was attached using double-sided foam adhesive tape. Each assembly, containing circuitry for preamplification with a gain of 35, measured 33 × 17 × 10 mm. Each
*Therapeutics Unlimited, 2835 Friendship St, Iowa City, IA 52240.
assembly held two silver-silver chloride electrodes, which were 8 mm in diameter with a 20-mm distance between centers. Conductive gel filled the holes in the tape over the electrode sites. The electrode for the rectus femoris muscle was placed one half of the distance from the anterior superior iliac spine to the superior pole of the patella. The electrode for the biceps femoris muscle was located one third of the distance from the ischial tuberosity to the middle of the lateral joint line of the knee. For the gluteus medius muscle, the electrode was located one third of the distance along a line from the midpoint of the iliac crest to the greater trochanter. The electrode for the vastus medialis muscle was applied over the muscle belly found by visually inspecting the thigh while the subject exerted a strong isometric contraction of the quadriceps femoris muscle. In all instances, the electrode assembly was aligned with the direction of the muscle fibers. A common ground electrode was positioned over the right fibular head, and all electrode leads were plugged into main amplifiers.
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RESEARCH Instrumentation
The combined preamplifier and main amplifier system permitted a gain of 100 to 10,000 with a bandwidth of 7 Hz to 6 kHz. After amplification, the EMG signals were full-wave rectified and low-pass filtered (with a cut-off frequency of 8 Hz) to produce a linear envelope. The EMG signals then were cabled to either an Apple IIe computer,† through a Cyborg Biolab System,‡ or to an IBM PC computer.® The change in the computer was due to an upgrade in data management capability after nine subjects had been tested. Software for operation of the two computers allowed for use of the same sampling rates and data manipulation, certifying consistency during all data collection. All EMG data were sampled at a rate of no less than 100 samples per second. Although the EMG preamplifier system minimizes artifact, at least two channels of raw EMG were evaluated continuously for offsets and artifacts on a standard oscilloscope. All four channels were evaluated periodically for each subject, and at no time did extraneous signals occur.
Protocol
The EMG data were recorded simultaneously from the four muscles during maximal, manually resisted SLR and QS exercises while the participant assumed a semi-Fowler's position on a standard plinth. Because measurement reliability of .72 to .85 had been established with Pearson product-moment correlation coefficients in an earlier study, the same protocol was adopted for this study.5
Because the EMG data were to be normalized, each participant's maximally evoked EMG recording for each of the specified muscles was selected from three trials of maximal effort isometric contraction completed in knee extension, knee flexion, and hip abduction with the knee extended. For this purpose, maximal voluntary contractions of the vastus medialis, rectus fe-moris, and biceps femoris muscles were completed at a clinically determined angle of 45 degrees of knee flexion.5 Maximal EMG responses from the gluteus medius muscle were recorded at an an
gle of 30 degrees of hip abduction with the knee in extension. Verbal commands of "ready," "set," and "push" or "pull" were given to the participants. For maximal isometric contractions and exercise trials, the EMG data were sampled for a total of three seconds. The participants were instructed to relax while the data were being stored on a computer disk.
In performing the QS exercises, subjects were instructed to press the back of their knee as hard as possible into a small towel that had been placed under the knee. For the SLR exercises, the leg first was elevated above the plinth on the command "set." Manual resistance to active contraction then was applied just proximal and distal to the knee on "push." Three trials of each exercise were completed in a predetermined randomized order with rest periods of about 30 seconds to allow data storage.
Design and Data Analysis
The experimental research design was considered to be a two-factor mixed design based on independent groups (ie, healthy subjects vs patients) and repeated measures according to type of exercise (ie, SLR vs QS). The EMG values from each muscle during the maximal effort extractions and values for each muscle in the three trials for each of the two exercises were used in the data analysis. The percentage of maximal EMG response was calculated for all trials, producing a data set in which all values for each participant were normalized to that participant. The descriptive statistics, including means and standard errors, were computed with a standard statistical package. A linear analysis of variance (ANOVA) was used to test for interaction and to compare data across groups and also across exercises for each of the muscle groups.
RESULTS
Descriptive data, including means and standard errors, are shown in Figures 1 and 2. The ANOVAs completed for each muscle are shown in Tables 3 through 6. Nonsignificant interactions and nonsignificant diagnosis main effects resulted for all four muscles evaluated. Significant exercise main effects are shown in each table. Figure 3 graphically represents the differences when the healthy subjects and patients are combined into one group.
DISCUSSION The means and standard errors for
the respective muscle groups and exercises shown in Figures 1 and 2 graphically depict the differences in muscle activity found in this study. No statistical tests for differences between muscles could be completed because of limitations inherent in across muscle and channel comparisons of EMG data. No between-group (diagnosis) differences were demonstrated. The exercises, of primary interest in this study, produced obvious differences. The rectus femoris and vastus medialis muscles displayed opposite patterns of activity, with the vastus medialis, gluteus medius, and biceps femoris muscles demonstrating much greater activity during the QS exercises than during the SLR exercises (Fig. 3).
Current data and data from the previous study of Soderberg and Cook, although showing some difference in the mean values, agree well (Fig. 4).5 Some variance among groups of participants was anticipated, even with the testing of essentially equal proportions of right and left legs. Other factors such as the application of resistive loads by different investigators also may have been responsible. Review of the data shows that the quadriceps femoris muscles produced lower percentages of maximal EMG values in this study, whereas the other two muscles studied showed increased levels of activity (Fig. 4). In general, no systematic trend was apparent. Further review of data across trials indicated no orderly patterns associated with the trial in which participants reached the maximal EMG value.
The magnitude of the mean values demonstrated clear differences in the muscles used and the level of activity produced in the different contractions (Fig. 3). The hypothesis, therefore, that EMG data obtained from SLR and QS exercises would be similar in healthy subjects and in patients with knee pathologies is accepted. We could not compare our data to other studies because no similar calculations or comparisons of exercises have been reported. Even Skurja et al, who reported similar results for the vastus medialis and rectus femoris muscles, did not provide any numerical data.4
The results of this study agree with Pocock's findings of relatively large levels of EMG activity recorded during QS exercises.1 Although recognizing that a shorter muscle length would explain greater EMG activity, we believe that
† Apple Computer, Inc, 20525 Mariani Ave, Cupertino, CA 95014.
‡ Cyborg Corp, 343 Western Ave, Boston, MA 02135.
§ International Business Machines Corp, PO Box 1328-S, Boca Raton, FL 33432.
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our results could not have been influenced significantly because the participants were asked only to clear their heel from the supporting surface during the SLR exercises. Although we recognize that the precise relationship of EMG activity to tension still is debated, EMG analysis is considered to be an appropriate measure for assessing the relative intensity of muscle activity produced during exercises of interest to the physical therapist. Our results also are consistent with the work of Gough and Ladley in that their "static" exercise consistently produced greater EMG activity than the SLR exercises.3 Their results should be considered with caution, however, because they allowed subjects to complete the last few degrees of knee extension with a 3-in|| block behind the knee.
In response to our previous work with healthy subjects, some clinicians suggested that the results could be affected by preceding the SLR exercises with the QS exercises. To address this issue, with particular interest in how the vastus me-dialis and rectus femoris muscles would respond, we requested 11 of the healthy subjects and 10 of the patients with knee pathologies to complete an additional series of exercises. Each participant completed three more contractions, specifically performing the QS exercises before the SLR exercises. We termed the first phase of this exercise (ie, performance of QS exercises) the combined before (COB) phase, and the second phase (ie, performance of SLR exercises) was termed the combined after (COA) phase.
Because the design for this segment of the study was similar to that of the main study, this data set was analyzed using an ANOVA. Results showed that this smaller test subgroup demonstrated be-tween-exercise differences consistent with the results for the total groups of subjects. The ANOVA results revealed that the rectus femoris and vastus me-dialis muscles produced a significant interaction effect that precluded formal comparisons for main effects. Informal review of the data, however, showed that for both the rectus femoris and vastus medialis muscles the EMG activity was markedly increased when the COB phase was compared with either the QS exercises or the SLR exercises. For the rectus femoris muscle, the mean value for the COB phase was 125% of the maximal EMG values. The vastus medialis muscle increased to 161% of the
QSH
QSP
SLRH
SLRP
SE
Fig. 1. Percentage of maximal EMG activity for the rectus femoris and vastus medialis muscles for each type of exercise (QS = quadriceps femoris muscle setting, SLR = straight-leg-raising) by group (H = healthy subjects, P = patients with knee pathologies). SE is the standard error, pooled across exercise within groups.
QSH
QSP
SLRH
SLRP
SE
Fig. 2. Percentage of maximal EMG activity for the biceps femoris and gluteus medius muscles for each type of exercise (QS = quadriceps femoris muscle setting, SLR = straight-leg-raising) by group (H = healthy subjects, P = patients with knee pathologies). SE is the standard error, pooled across exercise within groups.
TABLE 3 Analysis of Variance Summary for Rectus Femoris Muscle
Source Group Subject Exercise Group x exercise
df 1
28 1 1
SS 2225.2
68648.5 24630.2 4059.4
F 1.59 1.76
17.65 2.91
P NS NS
.0002 NS
|| 1 in - 2.54 cm.
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RESEARCH
QSHP
SLRHP
Fig. 3. Graphic representation of the main effects, by muscle, shown by an analysis of variance. QSHP is quadriceps femoris muscle setting exercise data for healthy subjects and patients with knee pathologies combined. SLRHP is straight-leg-raising exercise data combined across groups.
QSB
QSC
SLRB
SLRC
Fig. 4. Comparison of the results of the current study with data from a previous study1 (QS = quadriceps femoris muscle setting, SLR = straight-leg-raising, B = previous study, C = current study).
TABLE 4 Analysis of Variance Summary for Vastus Medialis Muscle
Source Group Subject Exercise Group x exercise
df 1
28 1 1
SS 426.0
26024.5 22963.0
961.6
F 0.47 1.02
25.13 1.05
P NS NS
.0001 NS
mean value produced during the maximal effort trials. When compared with the values shown in Figure 3, this difference is dramatic, particularly because the only difference between the QS exercises and the COB phase was that the subjects' hands were placed on the anterior aspect of the leg so that resistance could be offered for the SLR component of the exercise that would produce the data for the COA phase. An explanation can be offered by the data of Haberichter et al who, studying the effects of sustained muscle pressure on the H-reflex, found that slight pressure to a muscle weakly facilitated its motoneuron excitability.13 This possibility of facilitatory effects of muscle pressure on these exercises is certainly of interest and potentially of great clinical import. No other explanations are readily apparent. Evaluation of the COA means 227% and 143% of maximal EMG values for the rectus femoris and vastus medialis muscles, respectively, compared with COB means of 125% and 161% of maximal EMG values show the expected direction in that the EMG activity of the rectus femoris muscle increased during the SLR phase, whereas the vastus medialis muscle decreased in EMG activity.
The ANOVA, including the combined exercises of COB and COA for the biceps femoris and gluteus medius muscles, produced nonsignificant interactions, thus allowing post hoc comparisons. Of the eight possible comparisons of the SLR and QS exercises to the COB and COA exercises, only the QS-COA comparison produced a nonsignificant correlation coefficient. Review of the mean values showed that for both muscles the EMG activity increased from between 17% and 55% (Fig. 3) to 72% and 111 % of the maximal values. This increased activity is probably of clinical significance, assuming that one of the objectives of using the QS exercises before the SLR exercises is to facilitate the contraction of the biceps femoris and gluteus medialis muscles. Although we found a demonstrable effect of this technique on the activity produced in these muscles, we can offer no specific explanation as to the causative factors.
Comment on the effects of knee effusion and surgery is necessary because both have been shown to be factors in the amount of EMG activity produced in postsurgical conditions. The importance of these factors was demonstrated in a recent study by Stratford in which severely effused knees produced a de-
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crease in EMG activity at 0 degrees of knee flexion when compared with 30 degrees of knee flexion.6 That none of the patients in our study had an acute or markedly effused knee makes any potential effect of these factors on our results unlikely. Clinicians should be aware of these factors and probably should heed the advice of Stratford who states that in these cases maximal isometric contractions of the quadriceps femoris muscle should be completed at 30 degrees of knee flexion.6
In another recent report, Krebs et al provide a review of the literature and new data to support the hypothesis that limbs that have undergone surgical procedures are likely to demonstrate loss in ability to recruit motor units, thus affecting the EMG response.7 Their work demonstrated that the motor unit activity to joint angle relationship is normal preoperatively, and diminishes postoperatively, before returning to normal three weeks or more after surgery. Again, because none of our patients were tested immediately after surgery, the results of this study probably were not influenced. Clinicians, however, should note the recommendation of Krebs et al that the postarthrotomy quadriceps femoris muscles should be exercised with the knee slightly flexed to
TABLE 5 Analysis of Variance Summary for Gluteus Medius Muscle
Source Group Subject Exercise Group x exercise
df 1
28 1 1
SS 130.2
31325.0 3151.8
23.8
F 0.30 2.55 7.19 0.05
P NS .007 .01 NS
TABLE 6 Analysis of Variance Summary for Biceps Femoris Muscle
Source Group Subject Exercise Group x exercise
df 1
28 1 1
SS 962.8
61061.0 13852.4
16.3
F 2.05 4.65
29.54 0.03
P NS
.0001
.0001 NS
generate, simultaneously, maximum mechanical tension and motor unit activity.
CONCLUSION
This study clearly shows that the SLR and QS exercises, as commonly used by clinicians, have different effects on the level of muscular activity derived from the rectus femoris, vastus medialis, gluteus medius, and biceps femoris muscles. The results show that exercise selection will influence the degree of
muscular activity and assumably the intensity of the contraction required for the specified therapeutic purpose.
Acknowledgments. We thank Jan-ine Wolbers for her assistance with data collection and Tom Cook for his assistance with computer programming. We also express appreciation to the physical therapists in the Musculoskeletal Division of the Department of Physical Therapy, The University of Iowa Hospitals and Clinics, for arranging for patient participation.
REFERENCES
1. Pocock GS: Electromyographic study of the quadriceps during resistive exercise. Phys Ther 43:427-434, 1963
2. Allington RO, Baxter ML, Koepke GH, et al: Strengthening techniques of the quadriceps muscles: An electromyographic evaluation. Phys Ther 46:1173-1176,1966
3. Gough JV, Ladley G: An investigation into the effectiveness of various forms of quadriceps extension. Physiotherapy 57:356-361, 1971
4. Skurja M Jr, Perry J, Gronley J, et al: Quadriceps action in straight leg raise versus isolated knee extension (EMG and tension study). Abstract. Phys Ther 60:582, 1980
5. Soderberg GL, Cook TM: An electromyographic analysis of quadriceps femoris muscle
setting and straight leg raising. Phys Ther 63:1434-1438,1983
6. Stratford P: Electromyography of the quadriceps femoris muscles in subjects with normal knees and acutely effused knees. Phys Ther 62:279-283, 1982
7. Krebs DE, Staples WH, Cuttica D, et al: Knee joint angle: Its relationship to quadriceps femoris activity in normal and postarthrotomy limbs. Arch Phys Med Rehabil 64:441-447, 1983
8. Wild JJ, Franklin TD, Woods GW: Patellar pain and quadriceps rehabilitation: An EMG study. Am J Sports Med 10:12-15,1982
9. Moller BN, Krebs B, Tidemand-Dal C, et al: Isometric contractions in the patellofemoral
pain syndrome: An electromyographic study. Arch Orthop Trauma Surg 105:24-27,1986
10. Antich TJ, Brewster CE: Modification of quadriceps femoris muscle exercises during knee rehabilitation. Phys Ther 66:1246-1250,1986
11. Lieb FJ, Perry J: Quadriceps function: An electromyographic study under isometric conditions. J Bone Joint Surg [Am] 53:749-758, 1971
12. Duarte-Cintra A, Furiani J: Electromyographic study of the quadriceps femoris in man. Elec-tromyogr Clin Neurophysiol 21:539-554, 1981
13. Haberichter PA, Mueksch AE, Rohrberg MG, et al: Muscle pressure effects on motoneuron excitability. Abstract. Phys Ther 65:723,1985
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