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. Using computational modeling of choice behavior, however, we found that the Force biofeedback condition, which required compensatory neuromuscular activation, caused a significantly greater increase in the subjective cost of effort than EMG biofeedback. By combining neuromuscular manipulation with computational modeling, our study demonstrates how various physiological processes affect feelings of fatigue and decisions to exert effort in response to fatiguing exertions. These results suggest that fatigue may consist of separate components that collectively serve to motivate behavior while simultaneously protecting and restoring bodily homeostasis amid physical challenge.