Effectiveness of eccentric and concentric strength training in patients with subacromial impingement syndrome

We aimed to compare the effects of eccentric and concentric strengthening on pain, strength, joint position sense (JPS) and function in patients with subacromial impingement syndrome (SIS). Forty-five patients with SIS were randomized equally to eccentric strength training (ESG), concentric strength training (CSG) and control (CG) groups. Hot pack, Transcutenal Neuromuscular Electrical Stimulation, posture, and mobility exercises was applied to all groups. ESG and CSG received eccentric and concentric strengthening, respectively. Shoulder rest and activity pain with visual analog scale, isometric and eccentric external rotation (ER) and abduction strength with a handheld dynamometer, JPS measured at abduction, ER, and internal rotation with inclinometer, and function with Constant-Murley Score (CMS) and Disabilities of the Arm, Shoulder and Hand (DASH) were assessed at baseline, after 12-weeks of treatment, and at 24-weeks follow-up. After treatment, activity pain decreased in ESG compared to CG (p=0.003) and the difference was maintained at the follow-up (p=0.032). Eccentric abduction strength increased in ESG compared to CG (p=0.021). Between baseline and follow-up, isometric and eccentric abduction strength increased in ESG compared to CSG (p=0.008 for isometric, p=0.010 for eccentric) and CG (p=0.010 for isometric, p=0.001 for eccentric). After treatment, eccentric abduction strength increased in CSG compared to CG (p=0.021). The abduction JPS improved in ESG compared to CG (p=0.011) and the difference was maintained at follow-up (p<0.001). CMS improved more in ESG than CSG (p=0.023) and CG (p=0.007) and differences were maintained (p<0.050). Other between-group comparisons were not significant (p>0.050). In SIS, eccentric strengthening is more successful than concentric strengthening to improve abduction strength and function, and than physiotherapy program including physical modalities and mobility exercises to improve shoulder pain, abduction strength and JPS, and function. Both strengthening regimens have no adjunct benefit to the effects of a combination of physical modalities and mobility exercises in improving DASH.