Effect of fatigue on maximal velocity and maximal torque during short exhausting cycling

A group of 24 subjects performed on a cycle ergometer a fatigue test consisting of four successive all-out sprints against the same braking torque. The subjects were not allowed time to recover between sprints and consequently the test duration was shorter than 30 s. The pedal velocity was recorded every 10 ms from a disc fixed to the flywheel with 360 slots passing in front of a photo-electric cell linked to a microcomputer which processed the data. Taking into account the variation of kinetic energy of the ergometer flywheel, it was possible to determine the linear torque-velocity relationship from data obtained during the all-out cycling exercise by computing torque and velocity from zero velocity to peak velocity according to a method proposed previously. The maximal theoretical velocity (ν1) and the maximal theoretical torque (T1) were estimated by extrapolation of each torque-velocity relationship. Maximal power (Pmax) was calculated from the values of T0 and ν0 (Pmax = 0.25ν0T0). The kinetics of ν0, T0 and Pmax was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal muscle strength and maximal power). Fatigue induced a parallel shift to the left of the torque-velocity relationships. The ν0, T0 and Pmax decreases were equal to 16.3%, 17.3% and 31%, respectively. The magnitude of the decrease was similar for ν0 and T0 which suggested that Pmax decreased because of a slowing of maximal shortening velocity as well as a loss in maximal muscle strength. However, the interpretation of a decrease in cycling ν0 which has the dimension of a maximal cycling frequency is made difficult by the possible interactions between the agonistic and the antagonistic muscles and could also be explained by a slowing of the muscle relaxation rate.