Changes in Motor Coordination Induced by Local Fatigue during a Sprint Cycling Task

PURPOSEThis study investigated how muscle coordination is adjusted in response to a decrease in the force-generating capacity of one muscle group during a sprint cycling task. METHODSFifteen participants were tested during a sprint before and after a fatigue electromyostimulation protocol was conducted on the quadriceps of one leg. Motor coordination was assessed by measuring myoelectrical activity, pedal force, and joint power. RESULTSThe decrease in force-generating capacity of the quadriceps (−28.0% ± 6.8%) resulted in a decrease in positive knee extension power during the pedaling task (−34.4 ± 30.6 W; P = 0.001). The activity of the main nonfatigued synergist and antagonist muscles (triceps surae, gluteus maximus and hamstrings) of the ipsilateral leg decreased, leading to a decrease in joint power at the hip (−30.1 ± 37.8 W; P = 0.008) and ankle (−20.8 ± 18.7 W; P = 0.001). However, both the net power around the knee and the ability to effectively orientate the pedal force were maintained during the extension by reducing the coactivation and the associated negative power produced by the hamstrings. Adaptations also occurred in flexion phases in both legs, exhibiting an increased power (+17.9 ± 28.3 [P = 0.004] and +19.5 ± 21.9 W [P = 0.026]), associated with an improvement in mechanical effectiveness. CONCLUSIONThese results demonstrate that the nervous system readily adapts coordination in response to peripheral fatigue by (i) decreasing the activation of adjacent nonfatigued muscles to maintain an effective pedal force orientation (despite reducing pedal power) and (ii) increasing the neural drive to muscles involved in the flexion phases such that the decrease in total pedal power is limited.