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

Abstract

ObjectiveRecent 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.PurposeThe aim of the current work was to examine the contribution of maximum strength (τmax), 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.MethodsThirty-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, τmax, CT, electromechanical delay (EMD), root-mean squared (RMS) amplitude, peak-to-peak voltage (Vpp), and Q30 were calculated.ResultsAn ANCOVA showed that τmax 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, τmax, 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.ConclusionThe 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.

Effects of the Proprioceptive Neuromuscular Facilitation Contraction Sequence on Motor Skill Learning-Related Increases in the Maximal Rate of Wrist Flexion Torque Development

“…It is somewhat surprising that there was no significant difference in the rate of muscle activation across test sessions, as has been previously observed (Van Cutsem et al, 1998;Barry et al, 2005;Inglis et al, 2017). There are two possible factors that interact to explain the present results.…”

“…Electromechanical delay has been observed to decrease with increases in the rate of muscle activation associated with motor-skill learning of maximal effort contractions ( Inglis et al, 2017 ), and has been linked with changes in motor unit activity ( Van Cutsem et al, 1998 ; Van Cutsem and Duchateau, 2005 ; Del Vecchio et al, 2019b ; Kirk and Rice, 2021 ). It is reasonable to suggest that the decrease in EMD observed in the present study, was indicative of alterations in rate coding due to motor skill learning, but the magnitude of change was not sufficient to detect changes in the rate of muscle activation ( Q 30 ), as would occur in a muscle with a larger recruitment range and/or following progressive resistive exercise training.…”

“…The rate of increase in FCR muscle activation was calculated by numerically integrating linear envelope detected (60 Hz) sEMG activity, from the onset of torque development to the first 30 ms (Q 30 ). This definition is different from starting integration from the onset of sEMG (Inglis et al, 2013(Inglis et al, , 2017. The reason is that the onset of FCR sEMG activity to initiate maximal isometric wrist flexion for the experimental group, occurs during maximal isometric wrist extension.…”

Neuromuscular recruitment strategies of the vastus lateralis according to sex

“…These contractions-induced alterations may be the result of the activation of larger MU fibres with greater conduction velocity during higher level contractions. 37,38 Increases in NFM instability, as measured by NFM jiggle or NFM segment jitter, can reflect increases in neuromuscular junction (NMJ) transmission instability with age 22,[39][40][41] and in diabetic neuropathy. 3 In the current study, NFM instability, as measured by NFM jiggle, increased with contraction level for both sexes, and to similar extents.…”

Weightlifting for Children and Adolescents: A Narrative Review

“…Absolute electromechanical delay times, contraction times, RFD, and power output are typically lower in female compared with male athletes. 40,55,113,131 Some of these differences may be accounted for by androgen differences 19 and, as adolescence is reached (puberty), by menstrual cycle factors. These sex-linked characteristics can be related to differences in performance and injury rate between men and women.…”