Effects of Upper Trapezius Myofascial Trigger Points on Scapular Kinematics and Muscle Activation in Overhead Athletes

Prolonged overactivity of the upper trapezius muscle with myofascial trigger points might cause muscle fatigue and subsequently change scapular kinematics and associated muscular activities. Scapular kinematics and associated muscular activities were investigated in 17 overhead athletes with upper trapezius myofascial trigger points and 17 controls before and after a fatigue task. Participants performed a fatigue task requiring sustained isometric scapular elevation. The outcomes included scapular kinematics (upward/downward rotation, external/internal rotation, posterior/anterior tilt) that were tracked by the Polhemus FASTRAK (Polhemus Inc., Colchester, VT, USA) system with Motion Monitor software and muscular activities (upper trapezius, lower trapezius and serratus anterior) that were collected at 1000 Hz per channel using a 16-bit analog-to-digital converter (Model MP 150, Biopac systems Inc., CA, USA) with pairs of silver chloride circular surface electrodes (The Ludlow Company LP, Chocopee, MA) during arm elevation. Mixed ANOVAs were conducted to characterize the outcomes with and without a fatigue task in participants with myofascial trigger points. Decreased scapular posterior tipping during 90 degrees of arm raising/lowering (effect sizes of 0.51 and 0.59) was likely to be elicited by the scapular elevation fatigue task in the presence of myofascial trigger points. Activity of the lower trapezius was higher in the myofascial trigger point group (6.2%, p = 0.036) than in the control group. Following the fatigue task, both groups showed increased activity in the upper trapezius (9.0%, p = 0.009) during arm lowering and in the lower trapezius (2.7%, p < 0.01) during arm raising and lowering. Decreased scapular posterior tipping during 90 degrees of arm raising/lowering after a fatigue task may lead to impingement. We found that the presence of upper trapezius myofascial trigger points in amateur overhead athletes was related to impaired scapular kinematics and associated muscular activities during arm elevation after a fatigue task, especially the decreased scapular tipping during 90 degrees of raising/lowering.