![]() When the shoulder muscles fatigue, joint mechanics become altered, thus possibly leading to rotator cuff pathologies. Since the glenohumeral joint is minimally constrained by articular anatomy, shoulder muscles are largely responsible for the dynamic stability. The effects of fatigue on peripheral muscles include reduced maximal voluntary force production, velocity of muscle contraction, and power output. The hypothesis being that a series of continuous repetitive muscle contractions will inevitably lead to reduced capability in the prime mover resulting in altered motor recruitment patterns to reduce the load on the fatigued musculature. Shoulder muscle fatigue has been proposed as a possible link to explain the association between repetitive arm use and the development of rotator cuff disorders. Repetitive arm movements are a major component of several workplace tasks as well as many sporting and leisure activities. Several risk factors have been identified for the development of rotator cuff disorders, including repetitive use of the shoulder. This protocol could be used to induce local muscular fatigue in order to evaluate the effects of fatigue on shoulder kinematics or to evaluate changes in shoulder muscle endurance following rehabilitation. The protocol was performed without difficulty by all volunteers and took less than 10 minutes to perform, suggesting that it might be feasible for clinical practice. ![]() Furthermore, this study established that the resultant effects of fatigue of the proposed isotonic protocol were reproducible over time. ConclusionsĬhanges in muscular performance observed during and after the muscular endurance protocol suggests that the protocol did result in muscular fatigue. Maximal isometric strength was significantly decreased after the endurance protocol ( P 0.84). Paired t-tests were used to evaluate the reduction in shoulder strength due to the protocol, while intraclass correlation coefficients (ICC) and minimal detectable change (MDC) were used to evaluate its reliability. Maximal isometric shoulder strength tests were performed before and after the fatigue protocol to evaluate the effects of the endurance protocol and its reliability. The endurance protocol was performed by 36 healthy individuals on two separate occasions at least two days apart. Each subject performed 60 continuous repetitions of IR/ER rotation. The endurance protocol was performed in isotonic mode with the resistance set at 50% of each subject's peak torque as measured for shoulder external (ER) and internal rotation (IR). MethodsĪn endurance protocol was developed on a stationary dynamometer (Biodex System 3). Therefore, the purpose of this study was to establish a reliable protocol for objective assessment of shoulder muscle endurance. Such a test could improve clinical examination of individuals with shoulder disorders. To our knowledge, no standardized clinical endurance protocol has been developed to evaluate the effects of muscle fatigue on shoulder function.
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