A METHOD FOR ASSESSING MUSCLE FATIGUE DURING SPRINT EXERCISE IN HUMANS USING A FRICTION-LOADED CYCLE ERGOMETER

This study investigated the mechanical changes induced by muscle fatig ue caused by repeated sprints and determined whether a friction-loaded cycle ergometer has any advantages for assessing muscle fatigue. Nine subjects performed 15 sprints, each of 5 s with a 25-s rest, on a fri ction-loaded cycle ergometer. The averaged force, power and velocity o f each push-off were calculated. Maximal power decreased by 17.9%, wit h a concomittent slowing of muscle contraction, but without any change in the maximal force. These results demonstrated that repeated sprint s slow down muscle contraction, leading to a fall in maximal power wit hout any loss of force. This would suggest that fast twitch fibres are selectively fatigued by repeated sprints. However, the ergometer used in the present study made it difficult to evaluate the relative influ ences of contraction velocity and sprinting time. This was certainly t he most important limitation. On the other hand, it showed the advanta ge of measuring instantaneous power and total work dissipated in the e nvironment simultaneously. It also permitted a force-velocity relation ship to be obtained from a single sprint and this relationship is know n to be closely related to the muscle fibre composition.