What if muscle spindles were also involved in the sense of effort?

Effort perception is widely acknowledged to originate from central processes within the brain, mediated by the integration of an efference copy of motor commands in sensory areas. However, in this topical review, we aim to challenge this perspective by presenting evidence from neural mechanisms and empirical studies that suggest that reafferent signals from muscle spindles also play a significant role in effort perception. It is now imperative for future research (a) to investigate the precise mechanisms underlying the interactions between the efference copy and reafferent spindle signals in the generation of effort perception, and (b) to explore the potential for altering spindle sensitivity to affect perceived effort during ecological physical exercise and, subsequently, influence physical activity behaviours.