The potential role of upper extremity muscle fatigue in the generation of extrinsic subacromial impingement syndrome: a kinematic perspective

Abstract

Background:Subacromial impingement syndrome (SAIS) of the shoulder has a multi-factorial aetiology which includes both intrinsic and extrinsic mechanisms. Upper extremity muscle fatigue has been proposed as a potential causative factor in extrinsic SAIS development.Objectives:This review summarises the current state of knowledge regarding fatigue-induced glenohumeral (GH) and scapulothoracic (ST) kinematic changes as they relate to subacromial space reduction and subsequent SAIS. It specifically addresses evidence for mechanisms including superior humeral head translation and scapular reorientation.Major findings:Global upper extremity muscle fatigue elicits GH kinematic changes that increase SAIS risk. Concurrent compensatory ST kinematic alterations, primarily scapular upward rotation (UR), lessen this risk. Additionally, fatiguing protocols aimed to selectively exhaust certain muscles or muscle groups without fatiguing the rotator cuff were unsuccessful, suggesting that rotator cuff fatigue is likely for a wide range of fatiguing upper extremity tasks.Conclusions:Despite the compensatory response of scapular reorientation in fatigued conditions, the dimensions of the subacromial space still pose increased risk for SAIS development, and the variability in kinematic responses produces highly differential risk, particularly for those exposed to tasks requiring increased rotator cuff muscle demand.