Neural, biomechanical, and physiological factors involved in sex-related differences in the maximal rate of isometric torque development

Abstract

Objective

Recent research has reported that lower maximal rate of torque development (dτ/dt _max) exhibited by females, relative to males, during knee extension can be accounted for by normalization to a maximal voluntary contraction (MVC); however, this was not seen in the upper limb.

Purpose

The aim of the current work was to examine the contribution of maximum strength (τ_max), twitch contraction time (CT), muscle fiber condition velocity (MFCV), and rate of muscle activation (Q₃₀) to sex-differences in the dτ/dt _max during maximal isometric dorsiflexion.

Methods

Thirty-eight participants (20 males; 18 females) performed both maximal voluntary and evoked isometric contractions of the tibialis anterior across 3 days. Ten maximal compound muscle action potentials were elicited and subsequently followed by three, 5-s contractions. From the recordings, MFCV, dτ/dt _max, τ_max, CT, electromechanical delay (EMD), root-mean squared (RMS) amplitude, peak-to-peak voltage (Vpp), and Q₃₀ were calculated.

Results

An ANCOVA showed that τ_max accounted for all the sex-differences in dτ/dt _max (p = 0.96). There were no significant differences between groups with respect to MFCV, RMS amplitude, Vpp amplitude, or CT. However, there was a significant sex-difference in dτ/dt _max, τ_max, and Q₃₀. Females had longer evoked EMD times compared with males (15.69 ± 10.57 ms versus 9.95 ± 3.46 ms; p = 0.01), but the voluntary EMD times were not different.

Conclusion

The current research supports the work by Hannah et al. Exp Physiol 97:618–629, (2012) that normalization to MVC in the quadriceps is able to account for all sex-differences in rate of toque development in the lower limb.

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