15 male athletes who were skilled in throwing and who had chronic anterior instability of the shoulder (Group 1) were evaluated by dynamic intramuscular electromyography while pitching a baseball. Indwelling wire electrodes recorded the levels of activity in the biceps, middle deltoid, supraspinatus, infraspinatus, pectoralis major, subscapularis, latissimus dorsi, and serratus anterior throughout the entire pitching sequence. These signals were synchronized electronically with records of the pitch that were made using high-speed photography. The pitch was divided into 5 phases: wind-up, early cocking, late cocking, acceleration, and follow-through. The results were compared with previous identical studies of 12 healthy, uninjured male athletes who were skilled in throwing (Group 2). Activity increased mildly in the biceps and supraspinatus in Group 1 as compared with Group 2. Similar patterns of activity were demonstrated in the deltoid. In Group 1 the infraspinatus had increased activity during early cocking and follow-through but had decreased activity during late cocking. The pectoralis major, subscapularis, latissimus dorsi, and serratus anterior in Group 1 all were shown to have markedly decreased activity. The study revealed a difference between Groups 1 and 2 in all of the muscles of the shoulder that were tested with the exception of the deltoid. The mildly increased activity levels of the biceps and supraspinatus that were found in Group 1 may compensate for anterior laxity. The marked reduction in activity in the pectoralis major, subscapularis, and latissimus dorsi added to the anterior instability by decreasing the normal internal-rotation force that is needed during the phases of late cocking and acceleration. Diminished activity of the serratus anterior may decrease protraction of the scapula, causing the glenoid fossa to remain behind the forward-flexing humerus during the late cocking phase. Diminished protraction of the scapula increases anterior laxity due to increased stress of the humeral head on the anterior part of the glenoid labrum and capsule. The neuromuscular imbalance that is seen in the throwing athlete who has instability of the shoulder either is part of the primary pathology or is a secondary phenomenon. This study provides a basis for the development of a rehabilitation program for patients who have chronic anterior instability of the shoulder.
Copyright remains with the authors and publisher.
15 male athletes who were skilled in throwing and who had chronic anterior instability of the shoulder (Group 1) were evaluated by dynamic intramuscular electromyography while pitching a baseball. Indwelling wire electrodes recorded the levels of activity in the biceps, middle deltoid, supraspinatus, infraspinatus, pectoralis major, subscapularis, latissimus dorsi, and serratus anterior throughout the entire pitching sequence. These signals were synchronized electronically with records of the pitch that were made using high-speed photography. The pitch was divided into 5 phases: wind-up, early cocking, late cocking, acceleration, and follow-through. The results were compared with previous identical studies of 12 healthy, uninjured male athletes who were skilled in throwing (Group 2). Activity increased mildly in the biceps and supraspinatus in Group 1 as compared with Group 2. Similar patterns of activity were demonstrated in the deltoid. In Group 1 the infraspinatus had increased activity during early cocking and follow-through but had decreased activity during late cocking. The pectoralis major, subscapularis, latissimus dorsi, and serratus anterior in Group 1 all were shown to have markedly decreased activity. The study revealed a difference between Groups 1 and 2 in all of the muscles of the shoulder that were tested with the exception of the deltoid. The mildly increased activity levels of the biceps and supraspinatus that were found in Group 1 may compensate for anterior laxity. The marked reduction in activity in the pectoralis major, subscapularis, and latissimus dorsi added to the anterior instability by decreasing the normal internal-rotation force that is needed during the phases of late cocking and acceleration. Diminished activity of the serratus anterior may decrease protraction of the scapula, causing the glenoid fossa to remain behind the forward-flexing humerus during the late cocking phase. Diminished protraction of the scapula increases anterior laxity due to increased stress of the humeral head on the anterior part of the glenoid labrum and capsule. The neuromuscular imbalance that is seen in the throwing athlete who has instability of the shoulder either is part of the primary pathology or is a secondary phenomenon. This study provides a basis for the development of a rehabilitation program for patients who have chronic anterior instability of the shoulder.
Copyright remains with the authors and publisher.