Increased co-contraction of arm adductors is associated with a favorable course in subacromial pain syndrome.

Background Enhancement of arm adductor activity during abduction (ie, adductor co-contraction), may be effective in the treatment of subacromial pain syndrome (SAPS). We assessed whether an increase of adductor co-contraction is associated with a favorable course of SAPS. Methods At baseline and after nearly 4 years of follow-up, electromyography of the latissimus dorsi (LD), teres major (TM), pectoralis major, and deltoid muscle was obtained during isometric abduction and adduction tasks in 26 patients with SAPS. Changes in co-contraction were assessed with change in the activation ratio (Δ AR). The AR ranges between −1 and 1, where lower values indicate more co-contraction. Clinical course was determined from an anchor question (reduced, persistent, or increased complaints), the visual analog scale for pain (VAS), and the Western Ontario Rotator Cuff score (WORC). Results In patients indicating persistent complaints (31%), the VAS and WORC remained stable. In patients who indicated reduced complaints (69%), the VAS reduced (z score, −3.4; P =.001) and WORC increased (z score, 3.6; P <.001). Unchanged ARs associated with complaints persistence, whereas decreased AR of the LD (Δ AR LD , −0.21; 95% confidence interval [CI], −0.36 to −0.06) and TM (ΔAR TM , −0.17; 95% CI, −0.34 to −0.00) coincided with reduced complaints. There was a significant between-group difference in Δ AR LD (−0.35; 95% CI, −0.60 to 0.10) and Δ AR TM (−0.36; 95% CI, −0.66 to –0.05). Conclusions Increased co-contraction of the LD and TM is associated with a favorable course of SAPS. This may be explained by widening of the subacromial space accomplished by adductor co-contraction. [ABSTRACT FROM AUTHOR]