Muscle activity of shoulder joints in patients with multidirectional shoulder instability during pull, forward punch, elevation and overhead throw

Abstract. Multidirectional shoulder joint instability alters the role of dynamic stabilizers, as a result of which the motion patterns of muscles surrounding the shoulder joint are also changed. The aim of this study was to compare the muscle activity of patients with multidirectional shoulder instability and the control group during pull, forward punch and elevation and during overhead throw. Fifteen subjects with multidirectional shoulder instability and fifteen control subjects with normal, healthy shoulders participated in the study. Both shoulders were tested in all subjects. Signals were recorded by surface EMG from eight different muscles during pull, forward punch, elevation and overhead throw. The maximum values of normalized voluntary electrical activity, and the time span among peak muscle electrical activities in percent of total time of a movement cycle were compared with those of the healthy control group. Test results suggest that in the case of patients with multidirectional shoulder instability the different motions are performed in a different way. The results give rise to the assumption that the organism will attempt to ensure centralization of the glenohumeral joint and the reduction of instability is attempted to be ensured by the organism through increasing the role of rotator cuff