Patients with Subacromial Impingement Syndrome Exhibit Altered Shoulder Rotator Muscles Eccentric and Concentric Peak Torque

Background: Current conservative management of subacromial impingement syndrome (SIS) involves generic strengthening exercises, especially for internal (IR) and external (ER) shoulder rotators. So far, no study has directly investigated the difference in muscle strength between patients with SIS and normal subjects. Accordingly, the purpose of the current study was to compare the shoulder rotator muscles eccentric and concentric peak torque in patients with SIS and normal subjects. Methods: This study was a cross sectional research. Twenty-four patients with SIS (23.33±2.47 Years) and 24 normal subjects (22.83±2.15 Years), matched for hand dominance and physical activity level, completed isokinetic shoulder IR and ER testing. Within the SIS group, 18 patients had the symptoms in their dominant and 6 patients in their non-dominant side. The IR and ER strengths of both sides were measured separately using continuous reciprocal concentric and eccentric contraction cycles at speeds of 60 and 120 degrees per second, respectively. The values of peak torque were compared using independent t-tests between the SIS and normal groups. Results: Significantly lower concentric ER peak torque at 120 º/second (p = 0.016), eccentric ER peak torque at 60 º/second (p = 0.022), eccentric ER peak torque at 120 º/second (p = 0.043), and eccentric IR peak torque at 60 º/second (p = 0.036) and 120 º/second (p = 0.040) were identified in the symptomatic SIS group dominant shoulder compared to the control group dominant shoulder. Conclusion: Changes in eccentric and concentric peak torque in SIS group may be related to the limb dominancy, which may have clinical implications for strengthening regimes. Therefore, clinicians’ and therapeutic exercise expertise may benefit from eccentric isokinetic exercises for shoulder IR and ER rotators in order to design a treatment plan for patients with SIS.