Motor unit manifestations of muscle fatigue during dynamic leg extension exercises

Using a novel decomposition system capable of tracking the firing behaviour of motor units during dynamic tasks, we investigated for the first time the control of motor units during fatiguing dynamic flexion/extension contractions of the quadriceps muscle. We observed increasing motor unit firing rates and recruitment indicating that the excitation to the motoneuron pool increases to sustain the movement output as muscle fatigue develops. These findings are in agreement with those previously observed during isometric fatiguing tasks.