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

Recent research has reported that lower maximal rate of torque development (d tau/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. The aim of the current work was to examine the contribution of maximum strength (tau(max)), twitch contraction time (CT), muscle fiber condition velocity (MFCV), and rate of muscle activation (Q(30)) to sex-differences in the d tau/dt (max) during maximal isometric dorsiflexion. 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, d tau/dt (max), tau(max), CT, electromechanical delay (EMD), root-mean squared (RMS) amplitude, peak-to-peak voltage (Vpp), and Q(30) were calculated. An ANCOVA showed that tau(max) accounted for all the sex-differences in d tau/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 d tau/dt (max), tau(max), and Q(30). 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. 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.