Objective: The goal of this study was quantitative analysis of elbow range of motion (ROM) variability due to musculo skeletal fatigue.

Materials & Methods: Ten intact subjects using nonrandomized sampling were evaluated. Each subject performed four fatiguing tasks in two repetition rates using two weights that were 10 and 20 percent of their dynamic maximal voluntary contraction ability of non-dominant elbow flexion. The elbow range of motion (ROM), brachioradialis and biceps brachii activities were measured using an electrogoniometer and surface EMG electrodes. Detrended fluctuation analysis (DFA) was used to calculate ROM variability correlations. Effect of task condition was tested by Krusakl-Wallis test.

Results: Statistical analysis showed long term correlation between ROM fluctuations in three of the four tested conditions (0.5>&alpha&le1). This reveals the controlling role of central nervous system (CNS) during fatigue that in spite of the biomechanical differences between these three test conditions, long-term correlation coefficients were the same (P=0.548). The test condition with high load and low repetition rate differed significantly in comparison with other conditions (p=0.047). In this case the CNS played a minor role.

Conclusion: In rehabilitation or sports repetitive exercises, it is recommended to do high load activities with low repetition rates in a biomechanically controlled condition because such activities during fatigue may result in musculoskeletal injuries.