Electromyographic analysis of shoulder impingement syndrome versus normal subjects

Altered muscle activity in the scapulothoracic and glenohumeral muscles is commonly believed to be a factor contributing to shoulder impingement syndrome (SIS), then, the aim of the study was to determine and compare the activity pattern of the shoulder muscles in subjects with and without SIS. In this case-control study, 9 female subjects with shoulder impingement syndrome and 13 matched healthy female subjects were participated voluntarily by simple random sampling. Surface electromyography of serratus anterior, pectoralis major, upper trapezium, lower trapezium, posterior deltoid, anterior deltoid muscles of dominant side were recorded during D1ext and D1flex movement. Muscle activities were processed and compared in subjects with and without SIS. Non parametric test (Mann-Whitney Test)) was used for data analysis In both movement patterns, all muscles of the patient showed a greater normalized RMS than healthy group but this increase was statistically significant in anterior deltoid (p=0/003, p=0/04), pectoralis major (p=0/01, p=0/02), serratus anterior (p=0/01) and posterior deltoid (p=0/01) during D1ext and in lower trapezium (p=0/005,p=0/006) and pectoralis major (p=0/01) during D1flex. The results of this study indicate that patients with impingement symptoms show abnormal muscle activity. The findings support the theory that shoulders impingement may be related to altered muscle activity in the scapulothoracic and glenohumeral muscles.