Neural Adjustments during Repeated Braking and Throttle Actions on a Motorcycle Setup.

The aim of the study was to assess neuromuscular changes during an intermittent fatiguing task designed to replicate fundamental actions and ergonomics of road race motorcycling. Twenty-eight participants repeated a sequence of submaximal brake-pulling and gas throttle actions, interspaced by one maximal brake-pulling, until failure. During the submaximal brake-pulling actions performed at 30% MVC, force fluctuations, surface EMG, maximal M-wave (M) and H-reflex were measured in the flexor digitorum superficialis. At the end of the task, the MVC force and associated EMG activity decreased (<0.001) by 46% and 26%, respectively. During the task, force fluctuation and EMG activity increased gradually (106% and 61%, respectively) with respect to the pre-fatigue state (≤0.029). The M first phase did not change (≥0.524), whereas the H-reflex amplitude, normalized to M, increased (149%; ≤0.039). Noteworthy, the relative increase in H-reflex amplitude was correlated with the increase in EMG activity during the task (=0.63; <0.001). During the 10-min recovery, MVC force and EMG activity remained depressed (≤0.05) whereas H-reflex amplitude and force fluctuation returned to pre-fatigue values. In conclusion, contrarily to other studies, our results bring forward that when mimicking motorcycling brake-pulling and gas throttle actions, supraspinal neural mechanisms primarily limit the duration of the performance.