Muscular fatigue increases signal-dependent noise during isometric force production.

This study was designed to characterize the effect of fatigue on the relationship between muscular force and its variability over a broad range of submaximal forces. Eight participants had to match 4 levels of isometric force from 7 to 53% of their maximal capabilities. This task was repeated before and after a fatigue protocol that induced a loss of maximal force of approximately 31%. We found that, despite an increase in force variability that was proportional to the force level, the linear scaling of force variability with mean force was preserved during fatigue. Because this linear scaling is a prerequisite for optimal sensorimotor control models, our results broaden the explanatory power of these models to the fatigue case, while at the same time offering new routes towards understanding how the central nervous system adapts to fatigue.