The effects of scapular muscle fatigue on scapular sensorimotor system

Abstract

Muscle fatigue may affect scapular sensorimotor system severely because scapula is surrounded by lots of muscles, which not only provide proprioception but also control movements. However, the effects of scapular muscle fatigue on scapular joint position sense and kinematics are uncertain. The aims of this study are to investigate the effects of scapular muscle fatigue on scapular joint position sense and neuromuscular performances. We recruited 30 healthy adults. They received the measurements of scapular joint position sense (reposition error), muscle power, and kinematics during scaption (arm elevation in scapular plane) along with muscle activation before and after a fatigue protocol. Our fatigue protocol used repeatedly holding at modified push-up plus position to exhaust scapular muscles including upper, lower trapezius, and serratus anterior. Post-measurements would start when participants finished all repetitions or could no longer do one more repetition. The repeated measured analysis of variance (ANOVA) used to assess the effects of fatigue on scapular reposition error, muscle power, kinematics, and muscle activation. The level of statistical significance was set at P < 0.05. All subjects fatigued by confirming the median frequency of either one of three muscles dropped more than 10% during the last repetition. Muscle power of upper trapezius and serratus anterior dropped statistically significantly. Although the reposition error did not change, muscle activation of serratus anterior increased (18.746% to 26.344%, P = 0.006 in elevation; 15.217% to 27.406%, P = 0.037 in protraction) during joint position sense measurements. In 120° scaption, scapula decreased posterior tilt (13.813° to 10.334°, P = 0.000147); increased internal rotation (10.212° to 13.246°, P = 0.004); increased upperward rotation (52.776° to 54.351°, P = 0.005). Muscle activation of serratus anterior increased (65.914% to 84.611%, P = 0.002) in 90° ∼ 120° scaption. Scapular muscles fatigued did not alter scapular joint position sense, but neuromuscular performances such as scapular kinematics and muscle activation of serratus anterior were changed.