Purpose:
The aim of this study was to investigate the (electromyographic) EMG patterns of the shoulder muscles in asymptomatic swimmers with AGI – atraumatic glenohumeral instability. AGI, one of the most common shoulder disorders in athletes who perform overhead activities, occurs especially among swimmers. AGI usually provokes shoulder pain and secondary impingement syndrome, which might alter glenohumeral and scapular kinematics and change the activity of the shoulder muscles. Alternatively, pain or functional activities might affect EMG patterns in individuals with AGI.

Methods:
Eight swimmers with AGI and eight healthy swimmers took part in this cross-sectional study. Bilateral and simultaneous shoulder elevations in the scapular plane toward three different target distances were investigated, and the shoulder kinematics and EMG activities of the glenohumeral and scapulothoracic muscles were also collected. Results. No differences in the EMG patterns were found between swimmers with and without AGI in terms of the rate of EMG rise and magnitude.

Results:
No differences in the EMG patterns were found between swimmers with and without AGI in terms of the rate of EMG rise and magnitude.

Conclusions:
Shoulder instability does not necessarily affect the modulation of the shoulder muscles in swimmers with AGI. Others factors such as laxity in the capsular structures and ligaments may be one of the primary reasons for pain and instability in these athletes.