Differences in muscle activity with shoulder impingement syndrome for isometric conditions
MetadataShow full item record
Shoulder injuries are common in both the good producing and service providing industries. They have a major impact on the workplace due to long recovery time. One of the most common shoulder injury observed is impingement syndrome (IS), but a better understanding of this disorder is needed. Therefore, the main objective of this study is to identify and compare differences in muscle activation and coactivation patterns between individuals with a current diagnosis of shoulder impingement syndrome (IS, stage I and II), and individuals with no previous shoulder injury (control), for different isometric postures and forces exerted. For this study, 11 individuals with IS and 11 control individuals were recruited. Three postures or postural planes were studied (abduction, scaption and flexion). For each of the posture, four angle (30, 45, 60 and 80 degrees) and two force (0 and 2 lbs.) conditions were tested. For all conditions, the muscle activity (EMG) of the upper trapezius, middle trapezius, lower trapezius, serratus anterior, anterior deltoid, middle deltoid and posterior deltoid was measured. The results show significant differences in muscle activation and coactivation between the individuals with IS and the healthy controls. However, the muscles for which there were differences vary between the three main postures (abduction, scaption and flexion). In isometric abduction, the middle trapezius, lower trapezius, anterior deltoid, middle deltoid and posterior deltoid had significantly lower activity in individuals with IS compared to control individuals. In isometric scaption, the anterior deltoid had significantly lower activation in individuals with IS compared to control individuals, while the middle deltoid had greater activation. In isometric flexion, the serratus anterior and anterior deltoid had significantly lower activation in the individuals with IS, while the upper trapezius and posterior deltoid had greater activation. These results show differences in the equilibrium of the muscle activation and coactivation in the shoulder complex between individuals with IS and healthy individuals. To allow individuals with IS to obtain an equilibrium of the muscle activation and coactivation in the shoulder complex that is closer to the healthy group, rehabilitation strengthening exercises should directly target the muscles with lower activation while considering the conditions where such differences occur.