Latency and recruitment order of the shoulder muscles in dynamic complex movement in patients with shoulder impingement syndrome

Shoulder muscle timing is very important, however, study on the shoulder muscle timing and recruitment patterns is limited. Thus, the aim of the study was to determine and compare the timing and recruitment order of the shoulder muscles in subjects with and without Shoulder Impingement Syndrome (SIS). In this case-control study, 9 female subjects with shoulder impingement syndrome and 13 matched healthy female volunteer subjects selected by simple-non random sampling participated. Surface electromyography of serratus anterior, pectoralis major, upper trapezium, lower trapezium, posterior deltoid, and anterior deltoid muscles of dominant side were recorded during D1flex movement. Muscle latency time, relative muscle latency time and recruitment order were processed and compared in subjects with and without SIS. Non parametric test [2 independent samples (Mann-Whitney U)] was used for data analysis In patient group some muscles showed a greater latency time than healthy group but this increase wasnt statistically significant. Also, in patient group recruitment order of shoulder muscles was changed. Altered recruitment patterns of one or more muscles in the patient group as compared to healthy group indicate neuromuscular control has changed. Thus rehabilitation programs should be designed to restore and optimize the activation sequences and motor control of these muscles.