The effects of muscle fatigue on scapulothoracic joint position sense and neuromuscular performance

Fatigue of the scapular musculature might affect the sensorimotor system and neuromuscular control and therefore impair the dynamic alignment of the scapula. The purpose of this study was to investigate the effects of scapular muscle fatigue on joint position sense and the neuromuscular performance of the scapulothoracic joint.

Thirty healthy subjects were recruited. The joint position sense (measured as reposition errors during the scapular elevation and protraction task) of the scapulothoracic joint and scapular kinematics and muscle activation (% of maximum voluntary isometric contraction) during scaption, shoulder elevation in the scapular plane, before and after the fatigue task (modified push-up) were measured. The repeated measures analysis of variance (ANOVA) was used to assess the effects of fatigue on scapular reposition error and neuromuscular control.

Although joint reposition sense did not change after fatigue, muscle activation of the serratus anterior increased significantly (18.5%-26.3%, p = 0.006, elevation task; 15.2%-27.4%, p = 0.037, protraction task). At 120° scaption, the scapula showed a decreased posterior tilt (13.8°-10.3°, p < 0.001), increased protraction (10.2°-13.3°, p = 0.004) and lateral rotation (52.8°-54.4°, p = 0.005). Muscle activation of the serratus anterior increased (65.9%-84.6%, p = 0.002) during 90°-120°scaption.

Scapular muscle fatigue did not alter the scapulothoracic joint position sense, but increased serratus anterior activation and resulted in a more anteriorly tilted, protracted, and laterally rotated scapula during scaption. Whether or not these fatigue-related changes are linked to the development of shoulder problems needs to be investigated further.