DYNAMIC LOADING ON THE HUMAN MUSCULOSKELETAL SYSTEM - EFFECT OF FATIGUE

Objective. A study was conducted to investigate the effects of fatigue on the ability of human musculoskeletal system to deal with the onsla ught of the heel strike initiated shock waves. Design. Running on a tr eadmill at the anaerobic threshold level for 30 min was used to acquir e the experimental data on the foot strike initiated shock waves. Back ground. Muscles act to lower the bending stress on bone and to attenua te the dynamic load on human musculoskeletal system. Fatigue may dimin ish their ability to dissipate and attenuate loading on the system. Kn owledge of the effects of fatigue on the ability of the human musculos keletal system to attenuate the shock waves may help in design of the training procedures and exercises. Methods. Twenty-two young healthy m ales participated in this study. Each one was running on the treadmill at the speed corresponding to his anaerobic threshold for 30 min. The heel strike induced shock waves were recorded every 5 min on the tibi al tuberosity and sacrum. The data obtained were analyzed in both temp oral and frequency domains. Results. The results reveal significant in crease in the dynamic loading experienced by the human musculoskeletal system with fatigue. This may be attributed to the inability of the f atigued system to provide an efficient way to attenuate shock waves. C onclusions. The analysis of the recorded signals suggests that fatigue contributes to the reduction of the human musculoskeletal system's ca pacity to attenuate and dissipate those shock waves. This capacity app ears to be a function not only of the fatigue level, but also of the v ertical location along the skeleton.