Associations between voluntary activation and difference in critical torque estimation between gold standard methods in untrained participants

Abstract

Purpose. While motor unit recruitment may be impaired for some clinical populations, and while allout testing procedures involve repeated maximal contractions to accurately estimate critical torque (CT), no previous study has precisely examined the relationships between voluntary activation (VA) and difference in CT estimation according to gold-standards methods. The aim of the present study was to investigate whether the level of VA influences the CT estimated according to the two reference methods. Methods. In the present study, CT was estimated during a 5-min all-out test involving the plantar-flexor muscles in untrained participants, separated in two groups including subjects with low levels of VA (VA_Low; ), and high levels of VA (VA_High; ). The participants performed 60 maximal isometric contractions (3s of contractions/2s of rest) and VA was estimated before, every six contractions and after the all-out test. Results. The major findings were that participants in the VA_Low group had lower CT than VA_High participants (p=0.02) and showed lower exponential curvature constant (τ; p<0.0001). Differences in CT estimation was accounted for by baseline VA and τ (~55% of variance). Conclusion. The present study demonstrates the inconsistency between two standard CT estimation methods and show that the differences are linked to the ability to produce MVCs. While CT is an important parameter for quantifying neuromuscular fatiguability in clinical populations, the all-out test is limited in its current form. We suggest new ways for estimating CT that rely less heavily on VA capacity, which would therefore be more adapted to participants subject to neuromuscular deconditioning.