ELECTROMYOGRAPHIC RECORDINGS IN SHOULDER MUSCLES DURING ECCENTRIC MOVEMENTS

The purpose of the present study was to investigate shoulder muscle ac tivity during eccentric muscle movements, and to determine whether ele ctromyograms in patients with joint laxity differed from those in norm al subjects. Five normal subjects and 6 patients with generalized join t laxity and shoulder instability were studied. Both shoulders were in vestigated. Normalized electromyograms were recorded during eccentric loaded movements from 8 shoulder muscles in parallel. Intramuscular fi ne wire electrodes were used for 3 muscles of the rotator cuff: subsca pularis, supraspinatus, and infraspinatus. Surface electrodes were use d for superficially located muscles: the anterior, middle, and posteri or parts of the deltoid, pectoralis major, and latissimus dorsi. A gen eral trend was an activation of several muscles rather than a single m uscle during all movements investigated. Patients with generalized joi nt laxity activated their supraspinatus and subscapularis muscles to a higher level during flexion and adduction movements than normal subje cts did. This might indicate a greater necessity for muscular activity to provide anterior shoulder stability in lax joints. Compared with c oncentric movements previously studied, results from this study showed that the magnitude of activation was significantly lower during eccen tric movements in normal subjects and in patients with joint laxity.