Neuromuscular Signals Shape Fatigue and Effort-Based Decision-Making in Humans

Physical fatigue influences our willingness to undertake effortful actions, yet the physiological signals driving this process are not well understood. We created a biofeedback paradigm to distinguish the effects of reduced muscle-force capacity from compensatory increases in neuromuscular activity on effort-based decision-making. Human participants made risky choices about prospective physical effort before and after repeated fatiguing exertions under two biofeedback conditions: force biofeedback, which required increased neuromuscular drive, and EMG biofeedback, which constrained the increase in neuromuscular drive. Both biofeedback conditions led to similar reductions in muscle strength and feelings of fatigue. However, we found that the Force biofeedback condition, which required compensatory neuromuscular activation, produced a significantly greater increase in the subjective cost of effort, thereby altering individuals effort-based decision-making more than EMG biofeedback. These findings demonstrate how muscle physiological processes influence feelings of fatigue and decisions to exert effort. Suggesting that fatigue may consist of separate components that collectively motivate behavior while simultaneously protecting and restoring bodily homeostasis during physical challenge.