Pharmacological blockade of muscle afferents and perception of effort: a systematic review with meta-analysis

Background The perception of effort (PE) provides information on task difficulty and influences physical exercise regulation and human behavior. This perception differs from other-exercise related perceptions such as pain. There is no consensus on the role of group III-IV muscle afferents as a signal processed by the brain to generate PE. Objective The aim of this meta-analysis was to investigate the effect of pharmacologically blocking muscle afferents on the PE. Methods Six databases were searched to identify studies measuring the ratings of perceived effort (RPE) during physical exercise, with and without pharmacological blockade of muscle afferents. Articles were coded based on the operational measurement used to distinguish studies in which PE was assessed specifically ( effort dissociated ) or as a composite experience including other exercise-related perceptions ( effort not dissociated ). Articles that did not provide enough information for coding were assigned to the unclear group. Results The effort dissociated group ( n =6) demonstrated a slight RPE increase with reduced muscle afferents feedback (standard mean change raw (SMCR), 0.39; 95%CI, 0.13 to 0.64). The group effort not dissociated ( n =2) did not reveal conclusive results (SMCR, −0.29; 95%CI, −2.39 to 1.8). The group unclear ( n =8) revealed a slight RPE decrease with reduced muscle afferents feedback (SMCR, −0.27; 95%CI, −0.50 to −0.04). Conclusions The heterogeneity in results between groups reveals that the inclusion of perceptions other than effort in its rating influences the RPE scores reported by the participants. The absence of decreased RPE in the effort dissociated group suggests that muscle afferents feedback is not a sensory signal of PE. Key points To date, there is no consensus on the neurophysiological signal processed by the brain to generate the perception of effort. Following a systematic search in six databases, this meta-analysis suggests that reducing afferent feedback from the working muscles via epidural anesthesia does not reduce perception of effort. This systematic review suggests that afferent feedback from the working muscles is not the neurophysiological signal processed by the brain to generate the perception of effort.