Changes in Shoulder Kinematics Following an Isokinetic Fatigue Protocol in Tennis Players

A typical tennis match can take 1 to 5 hours. Tennis serve can be divided into eight stages and three phases. Injuries usually happen in the cocking stage and acceleration phase of the serve, where it requires large shoulder range of motion and proper scapular motion, including sufficient scapular upper rotation, external rotation, and posterior tilt to produce a powerful serve. Altered shoulder kinematics are associated with shoulder injuries in tennis players, including delayed shoulder horizontal adduction, and early external rotation. Due to the long duration and repetition of activity in a match, fatigue may happen and result in decreases in sensory input, passive range of motion, ball speed, and muscle strength. These changes may further lead to altered glenohumeral and scapular kinematics. However, previous studies mainly focused on the effects of fatigue on scapular kinematics in constrain movements and applied different fatigue protocols, which lead to inconsistent results. Tennis serve in cocking stage and the acceleration phase require high activation of shoulder external rotators and internal rotators, including infraspinatus, pectoralis major, subscapularis, latissimus dorsi and serratus anterior. However, to our knowledge, no study has investigated how fatigue of shoulder rotators influences shoulder kinematic as well as scapular kinematics during the late cocking stage and acceleration phase of tennis serve. Therefore, the investigators aim to investigate whether fatigue of shoulder rotator affects shoulder kinematics in healthy tennis players during the late cocking stage and acceleration phase of tennis serve.This is a single group, pretest-posttest measurement study. In a fatigue protocol, investigators use an isokinetic dynamometer to induce fatigue of shoulder rotators. Outcome measures will be tested before and after the fatigue protocol, including peak torque of shoulder rotators, humerothoracic kinematics, scapulothoracic kinematics, and median power frequency recorded by a surface electromyography. Peak torque of shoulder rotators will be measured with an isokinetic dynamometer. Surface electromyography will be used to measure peripheral muscle fatigue by maximum voluntary isometric contraction. Humerothoracic kinematics and scapulothoracic kinematics during a functional tennis serve and scaption will be collected with a motion capture system.