Abstract
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. The aim of this meta-analysis was to investigate the effect of pharmacologically blocking muscle afferents on the PE. 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. 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). The heterogeneity in results between groups reveals that the inclusion of other perceptions 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 generating 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 reveals that reducing afferent feedback from the working muscles via epidural anesthesia does not reduce perception of effort. This systematic review emphasizes the role of the corollary discharge associated with the motor command as the signal processed by the brain to generate the perception of effort.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Statement and Declarations
Funding statement. MB is supported by the Canadian Institutes of Health Research through the Canada Graduate Scholarships – Master’s Frederick Banting and Charles Best grant, the “Formation de maîtrise” scholarship from the Fond de recherche en santé du Québec and an MSc scholarship from the Centre de recherche de l’Institut universitaire de gériatrie de Montréal (CRIUGM). BP’s research is supported by the Natural Sciences and Engineering Research Council of Canada—Discovery Grants Program.
Competing interests. The authors have no conflict of interest to disclose in respect to this manuscript.
Availability of data and material. All data and materials are available within the manuscript or in supplemental materials.
Code availability. Not applicable