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DOI: 10.1101/2023.05.24.541485

Neuromuscular fatigue reduces responsiveness when controlling leg external forces

P.Kudzia J. M. Wakeling S. N. Robinovitch J. M. Donelan
In legged movement, our legs push against the ground, generating external force vectors that enable agile movements. Neuromuscular fatigue can reduce agility by causing physiological changes, such as slowing muscle reaction time, altering proprioception, and delaying neuromuscular control. Fatigue may deteriorate the nervous system's control of leg external forces, contributing to reductions in agility. Here we investigated the effect of fatigue on the nervous system's performance in controlling the vertical component of leg external force ground reaction forces, and hypothesized that increased leg fatigue would lead to declines in both responsiveness and accuracy of leg force control. To test this hypothesis, we used an apparatus that allowed participants to exert controlled vertical forces with one leg against a force plate while immobilizing the rest of their bodies. Participants adjusted their leg external force to match step targets displayed on a screen. We induced fatigue by having participants maintain submaximal leg forces, and we measured leg force control performance between fatigue trials. Results showed a significant 26% reduction in mean maximum force production, leading to a substantial decline in leg force control responsiveness, as evidenced by a 23% increase in rise time and a 25% narrowing of bandwidth. However, fatigue did not significantly reduce leg force control accuracy. Understanding the effects of fatigue on leg force control can inform the development of strategies and technologies to sustain agile performance, even in the presence of fatigue.