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To describe the relationship of the pronator teres, flexor carpi radialis, flexor digitorum superficialis, and flexor carpi ulnaris muscles to the medial collateral ligament at 30 degrees, 90 degrees, and 120 degrees of elbow flexion, we dissected 11 cadaveric specimens. The flexor carpi ulnaris muscle is the predominant musculotendinous unit overlying the medial collateral ligament in the majority of cases and is the only one at 120 degrees of elbow flexion. The flexor digitorum superficialis muscle is the only other significant contributor. The medial collateral ligament is the primary stabilizer of the medial elbow with elbow flexion greater than 30 degrees, as in throwing. The flexor carpi ulnaris muscle, because of its position directly over the medial collateral ligament, and the flexor digitorum superficialis muscle, with its near proximity and relatively large bulk, are the specific muscles best suited to provide medial elbow support. This is especially relevant to overhand throwing athletes who encounter extreme valgus force across the elbow during the cocking and acceleration phases of the throwing motion. Exercise and conditioning of the medial elbow musculature, specifically the flexor digitorum superficialis muscle and the flexor carpi ulnaris muscle, may prevent injury or assist in rehabilitation of medial elbow instability, especially in overhand throwing athletes. [ABSTRACT FROM AUTHOR]

The purpose of this study was to describe and compare electrical activity patterns in 12 shoulder muscles during the breaststroke in 25 competitive swimmers who had normal shoulders and in 14 who had painful shoulders while they performed this stroke in a pool. The electromyographic analysis was synchronized with high-speed cinematography to discern phases of the breaststroke. Means, standard deviations, and t-tests were done for each phase. The differences in muscle activity between the two groups of swimmers demonstrated an increase in the internal rotators in the group with painful shoulders. They also demonstrated a decrease in the teres minor, supraspinatus, and the upper trapezius muscles. These factors increase the risk of impingement. Both the serratus anterior and teres minor muscles in the swimmers with normal shoulders consistently fired at or above 15% manual muscle test throughout the breaststroke cycle and were thus subject to fatigue. Based on these results, exercises for the breaststroke swimmer should be directed toward endurance training of the serratus anterior and teres minor muscles while balancing the internal and external rotators of the shoulder as well as the deltoid and supraspinatus muscles. [ABSTRACT FROM AUTHOR]

Using dynamic surface electrode electromyography, we evaluated muscle activity in 13 male professional golfers during the golf swing. Surface electrodes were used to record the level of muscle activity in the right abdominal oblique, left abdominal oblique, right gluteus maximus, left gluteus maximus, right erector spinae, left erector spinae, upper rectus abdominis, and lower rectus abdominis muscles during the golfer's swing. These signals were synchronized electronically with photographic images of the various phases of the golf swing; the images were recorded in slow motion through motion picture photography. The golf swing was divided into five phases: take away, forward swing, acceleration, early follow-through, and late follow-through. Despite individual differences among the subjects' swings, we observed reproducible patterns of trunk muscle activity throughout all phases of the golf swing. Our findings demonstrate the importance of the trunk muscles in stabilizing and controlling the loading response for maximal power and accuracy in the golfer's swing. This study provides a basis for developing a rehabilitation program for golfers that stresses strengthening of the trunk muscles and coordination exercises. [ABSTRACT FROM AUTHOR]

This study compared the electromyographic activity of normal (N=22), rehabilitated anterior cruciate ligament-deficient (N=8), and -reconstructed knees (N=10) while subjects performed activities. Each subject had evaluation of 8 muscles during 7 functional activities. Sixty-seven percent of the differences in the quadriceps muscle reflected increased activity in the vastus lateralis muscle of the rehabilitated group; 75% of the differences in the hamstrings muscles noted increased biceps femoris muscle activity in the rehabilitated group; 56% of the differences in the lower leg musculature showed increased tibialis anterior muscle activity in the rehabilitated group. Eighty-six percent of the statistically different intervals involved rehabilitated subjects demonstrating increased activity over reconstructed or normal subjects or both. The presence of a quadriceps-hamstrings muscles coordinated response was identified consistently in all 3 groups in each activity. This study supports surgical reconstruction for the anterior cruciate ligament-deficient knee. It also demonstrates the importance of the vastus lateralis, biceps femoris, and tibialis anterior musculature in the rehabilitation of the anterior cruciate ligament-deficient patient. The presence of a quadriceps-hamstrings muscles coordinated response indicates that mechano-receptors mediating this reflex arc exist in structures other than the cruciate ligament. [ABSTRACT FROM AUTHOR]

This study descibes the fine-wire electromyographic profile of the normal knee. Twenty-two subjects with no prior history of knee injury volunteered for the study. Each subject had fine-wire electromyographic evaluation of 8 muscles (vastus medialis oblique, vastus lateralis, rectus femoris, semimembranosus, biceps femoris, tibialis anterior, gastrocnemius, and soleus muscles) while performing 7 functional activities. The percentage of maximum manual test for each muscle during each phase of the activities was used to determine means and standard deviations for the group. Walking and ramp and stair ascending and descending produced similar electromyographic profiles. Running and cross-cutting demonstrated unique electromyographic profiles with an overall higher muscle activity than the previous 5 activities. A quadriceps-hamstrings muscles' coordinated response was identified consistently in each activity. These findings illustrate the integral nature of each of the 8 examined muscles in knee motion. Furthermore, this study demonstrates a coordinated response of quadriceps-hamstrings muscles in the normal knee and may more thoroughly define the coordinated activity of these 2 antagonist muscle groups. Finally, this study provides a framework within which various knee conditions can be compared and from which specific rehabilitation recommendations can be generated. [ABSTRACT FROM AUTHOR]

Lateral epicondylitis occurs frequently in tennis players and appears to be caused by tears in the extensor aponeurosis. The purpose of this study was to compare the electromyographic activities of 5 muscles in players with lateral epicondylitis with those of injury-free players during the single-handed backhand tennis stroke. Fine-wire electrodes were placed into the extensor digitorum cummunis, extensor carpi radialis longus and brevis, pronator teres, and flexor carpi radialis muscles in competitive tennis players; 8 players had lateral epicondylitis and 14 had normal upper extremities. The backhand stroke then was recorded on high-speed film and synchronized with the electromyographic signal. The injured players had significantly greater activity for the wrist extensors and pronator teres muscles during ball impact and early follow-through. This activity increase may have been caused by the abnormal mechanics evident on film, including a 'leading elbow,' wrist extension and an open racquet face near the time of ball impact, and ball contact in the lower half of the strings. These mechanics not only result in a lower level of play but also leave the wrist extensors and the pronator teres muscles vulnerable to injury. This is the first study that documents increased activity in muscles that have been previously injured. [ABSTRACT FROM AUTHOR]

The purpose of this study was to describe and compare the muscle firing patterns of the muscles controlling the ankle during running. Fine-wire electrodes monitored the activity of the gastrocnemius, soleus, peroneus brevis, tibialis posterior, and tibialis anterior muscles during 3 paces of running. High-speed film was used to synchronize the electromyographic data with the phases of running. The subjects were 15 recreational and competitive runners who were injury-free. There were 3 significant findings. First, the firing patterns of all of the posterior muscles demonstrated peak activity during midstance phase. Thus, these muscles were contracting in an eccentric fashion to control ankle dorsiflexion as the center of gravity passed over the ankle. Second, the tibialis anterior muscle fired above the fatigue threshold for 85% of the time. This may account for the high number of fatigue-related injuries to the tibialis anterior muscle seen in runners. Third, there was a significant increase of activity in the peroneus brevis muscle as the pace increased. This indicates the importance of training this muscle when pace is increased. Using this information, a sport-specific effective and efficient exercise program for runners can developed. [ABSTRACT FROM AUTHOR]

It is generally believed that tennis players using a double-handed backhand rarely develop lateral epicondylitis since the helping arm appears to absorb more energy and changes the mechanics of the swing. The purpose of this paper was to compare muscle activity about the elbow in single- and double-handed backhand strokes in competitive tennis players. Muscle activity in 3 elbow extensors, a wrist flexor, and a forearm pronator of the dominant arm was compared during the single-handed (N=14) and double-handed (N=13) backhand ground strokes using indwelling electromyography and high-speed cinematography. Significantly higher activity was seen in the double-handed technique in the flexor carpi radialis muscle in the preparation phase and in the pronator teres muscle in the acceleration phase. Higher flexor carpi radialis muscle activity in preparation of the double-handed stroke appeared to be a function of the double-handed grip used on the racquet, and the increased pronator teres muscle activity in acceleration indicated maintenance of greater pronation provided by the grip of the nondominant hand. The decreased occurrence of lateral epicondylitis in players using a double-handed backhand may not be caused by decreased extensor activity, but rather by factors associated with flawed stroke mechanics more often seen in the single-handed technique. [ABSTRACT FROM AUTHOR]

Electromyography and high-speed film were used to examine the muscle activity in the elbows of pitchers with medial collateral ligament insufficiency compared to the activity in uninjured elbows. Ten competitive baseball pitchers with medial collateral insufficiency and 30 uninjured competitive pitchers were tested while throwing the fastball and the curveball. The extensor carpi radialis brevis and longus in the injured pitchers showed greater activity than in the uninjured pitchers for both pitches. The triceps, flexor carpi radialis, and pronator teres all showed less activity in the injured pitchers during the fastball, but only the triceps had less activity during the curveball. The differences were seen during the late cocking and acceleration phases, which place the greatest stress on the medial collateral ligament. If the flexor carpi radialis and pronator teres were substituting for the deficient medial collateral ligament and functioning as dynamic stabilizers, one would expect enhanced muscle activity. However, the opposite was found. This pattern of asynchronous muscle action with medial collateral ligament injury may predispose the joint to further injury. The muscular differences seen are critical to the understanding of the pathomechanics of patients with medial collateral ligament deficiency, and provide a basis for rehabilitation. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to describe the patterns of activity of 12 shoulder muscles in painful shoulders, and compare those patterns of activity with normal shoulders. The results show significant differences in 7 of the 12 muscles. Those muscles included the anterior deltoid, middle deltoid, infraspinatus, subscapularis, upper trapezius, rhomboids, and the serratus anterior. There were no significant differences between muscle activity patterns of normal versus painful shoulders in the latissimus dorsi, pectoralis major, teres minor, supraspinatus, or the posterior deltoid. This information will contribute to the development of muscle conditioning programs to optimize performance and prevent injury, as well as develop programs for scientific rehabilitation strengthening. [ABSTRACT FROM AUTHOR]

The shoulder in swimming is subjected to multiple factors that can lead to a high injury rate. To prevent injury, one must understand the biomechanics of swimming. This paper describes the electromyographic and cinematographic findings of 12 shoulder muscles in competitive swimmers without shoulder pain. The results show the three heads of the deltoid and the supraspinatus functioning in synchrony to place the arm at hand entry and exit, the rhomboids and upper trapezius to position the scapula for the arm, the pectoralis major and latissimus dorsi to propel the body, the subscapularis and serratus anterior as muscles with constant muscle activity, the teres minor functioning with the pectoralis major, and the infraspinatus active only to externally rotate the arm at midrecovery. This information is important to design optimal preventive and rehabilitative exercise programs. [ABSTRACT FROM AUTHOR]

Many exercises are used to strengthen the glenohumeral muscles, but there have been limited studies to evaluate the exercises. Thus, the purpose of this study was to decide how the muscles responsible for humeral motion can best be exercised in a rehabilitation program for the throwing athlete. Dynamic, fine wire, intramuscular electromyography was carried out in 15 normal male volunteers performing 17 shoulder exercises derived from a shoulder rehabilitation program used by professional baseball clubs. The four rotator cuff muscles were studied, as well as other positioners of the humerus, including the pectoralis major, latissimus dorsi, and three portions of the deltoid. The electromyographic activity was synchronized with cinematography and averaged over 30 degree arcs of motion. An exercise was considered to be a significant challenge for a muscle if it generated at least 50% of its predetermined maximum contraction over three consecutive arcs (i.e., a 90 degree range). Four exercises were consistently found to be among the most challenging exercises for every muscle. These shoulder exercises consisted of 1) elevation in the scapular plane with thumbs down, 2) flexion, 3) horizontal abduction with arms externally rotated, and 4) press-up. This study documents that the minimum for an effective and succinct rehabilitation protocol for the glenohumeral muscles would include these exercises. [ABSTRACT FROM AUTHOR]

Golf is a popular sport throughout the world, yet there is little in the literature that discusses the mechanics of the swing. The purpose of this study is to analyze the EMG activity in eight shoulder muscles of both the right and left arms during the golf swing. The results reveal that the infraspinatus and supraspinatus act predominantly at the extremes of shoulder range of motion, the subscapularis and pectoralis major during acceleration, the latissimus dorsi during forward swing, and the anterior deltoid during forward swing and follow-through. The middle and posterior deltoids appear to be relatively noncontributory, without any specific timing patterns. This data is an expansion of an earlier pilot study and allows us to more accurately develop an exercise program for optimal performance as well as for prevention and rehabilitation. [ABSTRACT FROM AUTHOR]

Background: Most surgical reconstructions of the separated acromioclavicular joint do not address the injured ligaments and capsule of the acromioclavicular joint., Purpose: This study was undertaken to compare the biomechanical characteristics of a modified Weaver-Dunn reconstruction and an intramedullary acromioclavicular joint reconstruction that uses a free-tissue graft for reconstruction of both the coracoclavicular and acromioclavicular ligaments., Study Design: Controlled laboratory study., Methods: Each pair of 6 matched pairs of cadaveric shoulders was randomly selected for a modified Weaver-Dunn reconstruction on 1 side and the contralateral side was used for free-tissue graft reconstruction of the coracoclavicular and acromioclavicular ligamentous complexes. Anterior-posterior and superior-inferior acromioclavicular joint translation (in millimeters) was measured with acromioclavicular joint compressions of 10, 20, and 30 N, and with translational loads of 10 and 15 N both before and after acromioclavicular joint reconstruction. Load-to-failure testing was then performed for each construct. Repeated-measures analysis of variance (translational testing) and Wilcoxon signed rank test (load-to-failure testing), both with P = .05, were used for statistical analysis., Results: Mean anterior-posterior and superior-inferior translation of the intramedullary acromioclavicular joint reconstruction was significantly less than that of the modified Weaver-Dunn under all loading conditions (P < .001 and P = .001, respectively), but was not significantly different from that of the intact state (P = .656 and P = .173, respectively). Although the mean ultimate and yield loads and linear stiffness for the intramedullary acromioclavicular reconstruction were greater than that of the modified Weaver-Dunn reconstruction, this did not reach statistical significance (P = .625, P = .625, and P = .625, respectively)., Conclusion: Acromioclavicular joint reconstruction with free-tissue graft for both the coracoclavicular and acromioclavicular ligamentous complexes demonstrates initial stability significantly better than a modified Weaver-Dunn and similar to that of intact specimens., Clinical Relevance: This acromioclavicular joint reconstruction provides the surgeon with a relatively nondestructive option.

The purpose of this study was to describe the activity of eight shoulder muscles during the windmill fast-pitch softball throw. Ten collegiate female pitchers were analyzed with intramuscular electromyography, high-speed cinematography, and motion analysis. The supraspinatus muscle fired maximally during arm elevation from the 6 to 3 o'clock position phase, centralizing the humeral head within the glenoid. The posterior deltoid and teres minor muscles acted maximally from the 3 to 12 o'clock position phase to continue arm elevation and externally rotate the humerus. The pectoralis major muscle accelerated the arm from the 12 o'clock position to ball release phase. The serratus anterior muscle characteristically acted to position the scapula for optimal glenohumeral congruency, and the subscapularis muscle functioned as an internal rotator and to protect the anterior capsule. Although the windmill softball pitch is overtly different from the baseball pitch, several surprising similarities were revealed. The serratus anterior and pectoralis major muscles work in synchrony and seem to have similar functions in both pitches. Although the infraspinatus and teres minor muscles are both posterior cuff muscles, they are characteristically uncoupled during the 6 to 3 o'clock position phase, with the infraspinatus muscle acting more independently below 90 degrees. Subscapularis muscle activity seems important in dynamic anterior glenohumeral stabilization and as an internal rotator in both the baseball and softball throws.

To describe the role of the scapular muscles in the golf swing, we studied 15 competitive male golfers. Four muscles were studied bilaterally using dynamic electromyography and cinematography. In the trailing arm, the levator scapulae elevates while the rhomboid muscles retract the scapula during takeaway; both then stabilize the scapula through the remainder of the swing. In the leading arm, these muscles retract the scapula during forward swing and acceleration. The trapezius muscle in the trailing arm also demonstrates high activity during takeaway to aid in scapular retraction. In the leading arm, trapezius activity is high in forward swing and through the remainder of the swing to promote scapular retraction. The serratus anterior muscle activity is high in the trailing arm during forward swing and through the remainder of the swing to maximize scapular protraction. In the leading arm, the serratus anterior muscle has constant activity through all phases of the swing, which may explain the clinical scenario of muscle fatigue in high demand golfers. The golf swing and uncoiling action requires that the scapular muscles work in synchrony to maximize swing arc and clubhead speed. This study demonstrates the importance of the scapular muscles in the golf swing and the need for specific strengthening exercises.

This study describes the fine-wire electromyographic profile of the normal knee. Twenty-two subjects with no prior history of knee injury volunteered for the study. Each subject had fine-wire electromyographic evaluation of 8 muscles (vastus medialis oblique, vastus lateralis, rectus femoris, semimembranosus, biceps femoris, tibialis anterior, gastrocnemius, and soleus muscles) while performing 7 functional activities. The percentage of maximum manual test for each muscle during each phase of the activities was used to determine means and standard deviations for the group. Walking and ramp and stair ascending and descending produced similar electromyographic profiles. Running and cross-cutting demonstrated unique electromyographic profiles with an overall higher muscle activity than the previous 5 activities. A quadriceps-hamstrings muscles' coordinated response was identified consistently in each activity. These findings illustrate the integral nature of each of the 8 examined muscles in knee motion. Furthermore, this study demonstrates a coordinated response of quadriceps-hamstrings muscles in the normal knee and may more thoroughly define the coordinated activity of these 2 antagonist muscle groups. Finally, this study provides a framework within which various knee conditions can be compared and from which specific rehabilitation recommendations can be generated.

This study compared the electromyographic activity of normal (N = 22), rehabilitated anterior cruciate ligament-deficient (N = 8), and -reconstructed knees (N = 10) while subjects performed activities. Each subject had evaluation of 8 muscles during 7 functional activities. Sixty-seven percent of the differences in the quadriceps muscle reflected increased activity in the vastus lateralis muscle of the rehabilitated group; 75% of the differences in the hamstrings muscles noted increased biceps femoris muscle activity in the rehabilitated group; 56% of the differences in the lower leg musculature showed increased tibialis anterior muscle activity in the rehabilitated group. Eighty-six percent of the statistically different intervals involved rehabilitated subjects demonstrating increased activity over reconstructed or normal subjects or both. The presence of a quadriceps-hamstrings muscles coordinated response was identified consistently in all 3 groups in each activity. This study supports surgical reconstruction for the anterior cruciate ligament-deficient knee. It also demonstrates the importance of the vastus lateralis, biceps femoris, and tibialis anterior musculature in the rehabilitation of the anterior cruciate ligament-deficient patient. The presence of a quadriceps-hamstrings muscles coordinated response indicates that mechanoreceptors mediating this reflex arc exist in structures other than the cruciate ligament.

The purposes of this study in the recreational runner were to describe and compare lower extremity sagittal range of motion and vertical body displacement for slow and fast paces during treadmill and overground running, and to compare timing of the running phases at the two paces. Vertical displacement of the body, and flexion and extension of the hip, knee, and ankle were measured with a motion analysis system at 200 hertz as the subjects self-selected the two paces. No statistically significant differences were seen when comparing sagittal motion on a treadmill with overground running. Statistically more vertical displacement during overground running was recorded when compared with treadmill running. Peak vertical force was near midstance when the ankle, knee, and hip approached maximum flexion. Results demonstrated that during a slow pace the approximate arcs of motion were: ankle, 50 degrees; knee, 95 degrees; and hip, 40 degrees. During running at a fast pace, the hip required more extension in early swing; the hip and knee required more flexion in middle and late swings. The fact that ankle motion did not change with the different speeds gave credence to the belief that push-off, or toe-off, is not the source of power in running.

The purpose of this study was to describe the firing pattern of 11 hip and knee muscles during running. Thirty recreational runners volunteered to run at 3 different paces with indwelling electromyographic electrodes while being filmed at 100 frames per second. Results demonstrated that medial and lateral vasti muscles acted together for knee extension during terminal swing and loading response, possibly providing a patella stabilizing role. The vastus intermedius muscle functioned with the other vasti, plus eccentrically controlled knee flexion during swing phase. The rectus femoris muscle fired with the vastus intermedius muscle and assisted the iliacus muscle with hip flexion. The hamstrings fired primarily to eccentrically control hip flexion. The adductor magnus, tensor fascia lata, and gluteus maximus muscles afforded pelvic stabilization while assisting with hip flexion and extension. Forward propulsion was provided mainly by hip flexion and knee extension, which is contrary to the view that posterior calf muscles provide propulsion during toe off. Faster running paces lead to increased activity in the muscles. This may lead to more injuries, primarily in the muscles that were contracting eccentrically.

Golf is a popular sport for both men and women. The trunk is the most common area of injury during the golf swing. The purpose of this study was to describe and compare the muscle firing patterns in the trunk during the golf swing. Twenty-three golfers with handicaps of five or below volunteered for this study. Surface electromyographic electrodes were placed on the abdominal oblique and erector spinae muscles bilaterally. High-speed cinematography was used in conjunction with the electromyographic electrodes. The results demonstrated relatively low activity in all muscles during takeaway (below 30% of maximal muscle test), and relatively high and constant activity throughout the rest of the swing (above 30% maximal muscle test, with the exception of the contralateral erector spinae during late follow-through, which was 28% maximal muscle test). This high and constant activity demonstrated the importance of the trunk muscles during a golf swing. These results indicate the need for an effective preventive and rehabilitative exercise program for the golfer.

The purpose of this study was to determine which exercises most effectively use the scapular muscles. Eight muscles in 9 healthy subjects were studied with indwelling electromyographic electrodes and cinematography while performing 16 exercises. The 8 muscles studied were the upper, middle, and lower trapezius; levator scapula; rhomboids; pectoralis minor; and the middle and lower serratus anterior. Each exercise was divided into arcs of motion and the electromyographic activity was quantified as a percentage of the maximal manual muscle test. The optimal exercises for each muscle were identified based on intensity (greater than 50% maximal manual muscle test) and duration (over at least 3 consecutive arcs of motion) of the muscle activity. Twelve of the exercises qualified as top exercises for all of the muscles. On further analysis, a group of 4 exercises was shown to make up the core of a scapular muscle strengthening program. Those 4 exercises include scaption (scapular plane elevation), rowing, push-up with a plus, and press-up.

Men and women both enjoy the game of golf. Special considerations are made for women, such as the courses on the professional tours. Thus, one can ask what differences might exist between men and women golfers. This study compares the electromyographic firing patterns of normal shoulder musculature in men and women professional golfers. Eight shoulder muscles (pectoralis major, latissimus dorsi, supraspinatus, infraspinatus, subscapularis, anterior, middle and posterior deltoids) were studied using indwelling electromyography. A visual analysis revealed that women tended to have slightly more activity during the takeaway and forward swing phases, and the men tended to have more activity during acceleration and follow-through. However, an independent two-tailed t-test (P = 0.05) showed these differences not to be statistically significant. This finding is in keeping with injury incidence data from the LPGA Tour, PGA Tour, and Senior PGA Tour, which showed that all three tours have a similar incidence of shoulder injuries. This study does not compare the relative strength of men and women, however.

Muscle activity about the elbow during tennis strokes in nine professional and collegiate level players was studied using indwelling EMG and high speed photography. Eight muscles were evaluated for the serve, forehand, and backhand strokes. The serve was divided into six stages and the ground strokes into four stages. EMG tracings were subjected to analog-to-digital conversion and a relative measure of quantity was obtained. Analysis of variance and Turkey tests were then done to assess statistical significance (P less than 0.05). The ground strokes showed low activity in all muscles tested during the preparation phase. During the acceleration phase, both the backhand and forehand showed a generalized increase in all muscle activity. Both strokes showed marked activity of the wrist extensors and, in addition, the forehand showed high activity in the brachialis and biceps. In the follow-through phase, there was a generalized decrease in muscle activity. The serve showed low activity in all muscles tested during the wind-up phase. The wrist extensors increased their activity in the cooking phase, with marked activity in late cooking. The pronator teres and the triceps showed increased activity in the acceleration phase. Follow-through phase showed low muscle activity except for the biceps, which increased in late follow-through. In conclusion, the muscles of the elbow help stabilize the elbow as a unit during the ground strokes in these high level players. Power in the serve comes from increased activity in the triceps and pronator teres. The predominant activity of the wrist extensors in all strokes may be one explanation for predisposition to injury.