Effects of Muscle Fatigue on Shoulder Proprioception

ABSTRACT

OBJECTIVE: To investigate the changes of shoulder proprioception in normal subjects, according to the direction of the evoked fatigue on the shoulder muscle group. METHOD: 20 healthy volunteers (14 males and 6 females, age 20~35 years) with entirely normal shoulders participated in this study. Before fatigue exercises, the proprioception tests were performed during active reposition (ARP) and passive reposition (PRP) of dominant shoulder, using isokinetic dynamometer, System 3 Pro (Biodex medical system, New York, USA). Three trials each of active and passive repositioning (2degrees/sec) were recorded. We also estimated the results of the peak torque shoulder movements. The subjects performed maximal efforts with five repetitions on the direction of flexion, abduction, internal rotation and external rotation. The mean values of maximal concentric voluntary contraction (MVC peak torque of each muscle group contraction) were recorded. We repeated fatigue exercises until the peak torque dropped to 30% three times consistently, then retested the proprioception of shoulder joints. We compared the proprioceptive changes of the shoulder with pre-fatigue test and post-fatigue test on the direction of shoulder movements. RESULTS: There were significant differences of shoulder proprioception between pre-fatigue test and post-fatigue test of ARP in shoulder abduction and external rotation (p<0.05). CONCLUSION: In our study, the proprioception of shoulder joint decreased more prominently on external rotation and abduction movements under severely provoked muscle fatigue around the shoulder joint.