Electromyographic analysis 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 the muscle around 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, elevation and 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 mean and standard deviation of MVE% for the different movement types and time broadness values during overhead throw were determined for each muscle in both groups and compared with each other. Test results suggest that in case of patients with multidirectional shoulder instability the various motions are performed in a different way. The results give rise to the assumption that the centralization of the glenohumeral joint and the reduction of instability are attempted to be ensured by the organism through increasing the role of rotator cuff muscles and decreasing the role of the deltoid, biceps brachii and pectoralis maior muscles. The analysis of time broadness shows that in patients with multidirectional shoulder instability, the time difference between the peaks of normalized voluntary electrical activity is significantly greater than in the control group.

Muscular activation patterns in swimmers with asymptomatic shoulder joint instability

“…In addition, previous studies also observed changes in EMG activity in individuals with multidirectional instability during different isokinetic shoulder movements [4]. Particularly, it was found that EMG activity of the anterior AD, BIC and TrIC decreased while the EMG activity of the infraspinatus increased for the group with shoulder instability compared with a control group [4].…”

“…In addition, previous studies also observed changes in EMG activity in individuals with multidirectional instability during different isokinetic shoulder movements [4]. Particularly, it was found that EMG activity of the anterior AD, BIC and TrIC decreased while the EMG activity of the infraspinatus increased for the group with shoulder instability compared with a control group [4]. In contrast, Barden et al [8] found no significant difference in EMG amplitudes during isotonic concentric/eccentric movements of the shoulder joint in individuals with multidirectional instability.…”

“…For example, such individuals demonstrated lower EMG activity in the anterior and middle deltoid muscles during shoulder flexions and abduction [7]. On the other hand, Illyes and Kiss [4] observed an increase in anterior deltoid muscle activity but no change of the middle deltoid during shoulder elevations. The anterior and middle deltoids, along with the scapular muscles, also showed no alterations in either their onset, duration, or magnitude of activation in recent studies [6,8].…”

“…AGI generally provokes shoulder pain and secondary impingement syndrome [2], which may lead to movement disorder (kinematic changes) and changes in shoulder muscle activity (EMG changes) [3][4][5]. For instance, some of the kinematic changes observed in individuals with AGI include altered scapular kinematics such as excessive scapular protraction and anterior tilt [6] or decreased scapular upward rotation [5] during upper-arm elevations.…”

“…Studies reporting on the EMG activity of the shoulder joint muscles in individuals with AGI have shown controversial results regarding their latency and magnitude during shoulder elevation movements [4]. For example, such individuals demonstrated lower EMG activity in the anterior and middle deltoid muscles during shoulder flexions and abduction [7].…”