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Summary: The purpose of this article is to describe the outcome of an arthroscopic examination and the pathology in symptomatic shoulders of 41 professional overhand throwing athletes. With the arm in the position of the relocation test, 100% of the subjects had either contact between the rotator cuff undersurface and the posterosuperior glenoid rim or osteochondral lesions. Other key findings included undersurface cuff fraying in 93%, posterosuperior labral fraying in 88%, and anterior labral fraying in 36% of the subjects. This study supports the concept of impingement of the posterior cuff undersurface with the posterosuperior glenoid rim in the overhand throwing athlete with shoulder pain.

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.

The medical collateral ligament is a common site of injury in baseball pitchers, causing substantial morbidity and loss of pitching time. Twenty-six skilled baseball pitchers with medial collateral ligament insufficiency were studied before surgery with high-speed cinematography and fine-wire electromyography of eight muscles around the elbow. Data from the pitchers with injured elbows were compared with data obtained from uninjured pitchers. The flexor carpi radialis muscle in the pitchers with medial collateral ligament deficiencies revealed significantly decreased firing during the acceleration and deceleration phase of the fastball when compared with that of the pitchers with normal elbows, and the flexor carpi radialis muscle was significantly depressed during the early cocking and deceleration phases. The extensor muscles revealed slightly increased activity in the injured elbows; however, this was not statistically significant. Although the muscles of the flexor pronator group (especially the flexor carpi ulnaris muscle and the flexor digitorum superficialis muscles) are anatomically positioned to provide dynamic stability of the elbow, they did not demonstrate increased electrical activity in pitchers with medial collateral ligament deficiencies. This finding suggests that the muscles on the medial side of the elbow do not supplant the role of the medial collateral ligament during the fastball pitch.

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.

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.

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 degrees 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 degrees 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.

Fifteen professional baseball pitchers underwent active pitching motion analysis of the abdominal oblique, rectus abdominis, lumbar paraspinous and gluteus maximus muscles bilaterally via surface electrode evaluation. Baseline resting and isometric maximum values were obtained and active data referenced against these for comparison. The muscle activity then was measured during the pitching sequence and analyzed in each of the five pitching phases. The abdominal oblique, lumbar paraspinous and rectus abdominis contralateral to the pitching arm and the ipsilateral gluteus maximus all had increases in activity level of 75 to 100% during the active pitching motion. Using these data indicating specific muscle group patterns with clinical and performance data, we hope to minimize injuries and maximize pitching performance.