Scapular Kinematic and Shoulder Muscle Activity Alterations in Overhead Athletes With/Without Upper Trapezius Myofascial Trigger Point After Muscle Fatigue

The investigators will recruit healthy overhead athletes with and without upper trapezius myofascial trigger point. Participants will be asked to perform a sustained scapular elevation task at their peak force until the force decrease 50 %, which indicates upper trapezius muscle fatigue. There are two purposes in the current study: (1) to compare the differences between overhead athletes with/without upper trapezius myofascial trigger point during arm elevation in scapular kinematics and muscles activities (2) to investigate the effects of upper trapezius muscle fatigue on scapular kinematics and muscles activities in overhead athletes with/without upper trapezius myofascial trigger point. The first hypothesis is that the subjects with upper trapezius myofascial trigger point will show significant difference in scapular kinematics and muscles activities when compared to subjects without upper trapezius myofascial trigger point. Besides, the investigators suggest that subjects with/without upper trapezius myofascial trigger point will show significant difference in scapular kinematics and muscles activities after upper trapezius muscle fatigue, especially in subjects with upper trapezius myofascial trigger point. The outcome measurements includes scapular kinematics (upward/downward rotation, external/internal rotation, posterior/anterior tilting) and muscles activities (upper trapezius, serratus anterior, lower trapezius).