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The purpose of this study was to describe the electromyographic (EMG) pattern and relative intensities of 8 shoulder muscles during the volleyball serve and spike in 15 professional or collegiate-level athletes. The EMG analysis was synchronized with high-speed cinematography to discern phases of the spike and serve. During the spike, the anterior deltoid and supraspinatus functioned together to elevate and place the humerus throughout all phases. During cocking the infraspinatus and teres minor acted together to rotate the humerus externally. In acceleration, however, these muscles behaved independently; activity of the teres minor remained high, whereas the activity of the infraspinatus declined. The anterior wall muscles functioned to decelerate the humerus during cocking and acted as internal rotators during acceleration. Muscle activities recorded for the serve followed similar patterns as those seen for the spike, but with lower amplitudes. These data illustrate the complex sequence of shoulder muscle activity necessary to play competitive volleyball.

The inability to perform the "liftoff" test has been attributed to a subscapularis muscle or tendon injury. The goals of this study were to evaluate the activity of the glenohumeral muscles during performance of the "liftoff" maneuver and to identify the most effective initial upper extremity placement that isolates the subscapularis musculotendinous unit. In the first phase of this study 15 subjects accomplished four proposed versions to the "liftoff" test while their intramuscular electromyographic activity in select glenohumeral muscles was recorded. The second phase of this study assessed the ability of five subjects with a nonfunctional subscapularis musculotendinous unit to perform the same proposed versions. On the basis of electromyographic data none of the proposed versions to the "liftoff" maneuver isolated the upper and lower subscapularis muscle from either the teres major, latissimus dorsi, posterior deltoid, or rhomboid muscles (p > 0.05). In the presence of a nonfunctional subscapularis musculotendinous unit, the subjects were able to perform all of the proposed versions of the "liftoff" maneuver except one: elevation of the dorsum of the hand from the posterior-inferior border of the scapula (maximum internal rotation test). Although significant electromyographic activity was generated in the potentially confounding shoulder girdle muscles during the maximum internal rotation "liftoff" test, a successful test appears to be dependent on the isolated glenohumeral internal rotation function of the subscapularis muscle.

This study compared the electromyographic activity of rotator cuff and scapular muscles between subjects with anterior instability and subjects with normal shoulders. Thirty-eight patients were studied; 23 had anterior instability that was subsequently surgically confirmed, and 15 had normal shoulders. Fine wire electrodes were inserted into the subscapularis (upper and lower portions), supraspinatus, infraspinatus, rhomboid, serratus anterior, and trapezius (upper and lower portions) muscles. Abduction, scapular plane abduction (scaption), and forward flexion were performed over the range of motion and later divided into 30 degrees intervals. In both abduction and scaption, the supraspinatus demonstrated significantly less electromyographic activity from 30 degrees to 60 degrees in shoulders with anterior instability compared with normal shoulders (p < 0.05). During all three motions, shoulders with anterior instability demonstrated significantly less electromyographic activity in the serratus anterior when compared with normal shoulders (p < 0.05). This occurred at 30 degrees to 120 degrees of abduction and at 0 degree to 120 degrees of scaption and forward flexion. None of the other muscles demonstrated significant differences. These differences during planar motions were similar to those demonstrated during challenging overhead sport motions. Early rehabilitation efforts should focus both on the rotator cuff and scapular muscles to establish smooth, coordinated shoulder motion.

As golf increases in popularity, more golfers seek the proper mechanics necessary for the perfect golf swing. Surprisingly little scientific work has been published on the contribution of the hip and knee muscles during the golf swing even though most professionals have recognized their vital contribution. Recent studies have described the electromyographic (EMG) muscle activity of the shoulder, back, and trunk during the golf swing. The purpose of this study was to describe the electrical muscle activity in seven hip and knee muscles of both the left (lead) and right (trail) leg in competitive golfers while performing the golf swing. Sixteen golfers were studied with indwelling electrodes and high-speed cinematography. The EMG was synchronized with the film to discern five phases of the golf swing. Means, SDs, and t-tests were done. The results revealed that the trail hip extensors and abductors in conjunction with the lead adductor magus initiated pelvic rotation during forward swing. The lead hamstrings maintained a flexed knee and provided a stable base on which pelvic rotation took place. The peak EMG muscle activity recorded in the hips and knees occurred in an earlier phase than that measured previously in the trunk and shoulder. This confirmed the sequential firing pattern of the hip and knee muscles that takes place during the competitive golf swing. Information gained from this study can be used by players and coaches to optimize performance and to minimize injury.

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.

Many exercises are used to strengthen the knee muscles, yet limited studies that evaluate the exercises exist. The purpose of this study was to describe and compare the muscle firing patterns in five knee muscles during five rehabilitative exercises, which were presumed either to strengthen a specific muscle group or to elicit a cocontraction. During short-arc knee extension, the medial and lateral vasti were significantly more active during the last 15 degrees of extension than during other arcs (p < .05). The short-arc knee extension with hamstring cocontraction demonstrated significantly more activity in the rectus femoris, vastus medialis oblique, and vastus lateralis than the biceps femoris and semimembranosus in the final 15 degrees of extension (p < .05). With isometric knee cocontractions, no significant difference in muscle activity occurred in any of the arcs tested. During squatting, the rectus femoris, vastus medialis oblique, and vastus lateralis were significantly more active than the biceps femoris and semimembranosus during the descending, holding, and arising phases (p < .05). This information offers suggestions in selecting optimal knee rehabilitation exercises.

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. Finewire electrodes were placed into the extensor digitorum communis, 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.

The muscle firing pattern in 12 muscles throughout the lower extremity, trunk, and upper extremity during the batting swing is described in this study. The two hamstring muscles studied and the gluteal muscle had a similar pattern of high muscle activity during pre-swing and early swing, and then rapidly diminished. The vastus medialis demonstrated peak activity between 95 and 110% maximum muscle test (MMT) throughout the swing phases and follow-through. The erector spinae demonstrated activity from 85 to 185% MMT during the swing phases. The abdominal obliques showed greater than 100% MMT during the swing phases and follow-through. The supraspinatus and serratus anterior showed relatively low muscle activity (less than 40% MMT). These results show that batting is a sequence of coordinated muscle activity, beginning with the hip, followed by the trunk, and terminating with the arms. Power in the swing is initiated in the hip, and therefore exercises that emphasize such strength development are indicated. The maintained, high muscle activity in the trunk muscles indicates a need for back and abdominal stabilization and rotation exercises. The relatively low level of activity in the four scapulohumeral muscles tested indicated that emphasis should be placed on the trunk and hip muscles for a batter's strengthening program.

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.

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 preventative and rehabilitative exercise programs.

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.