Neural, biomechanical, and physiological factors involved in sex-related differences in the maximal rate of isometric torque development.
OBJECTIVE
Recent research has reported that lower maximal rate of torque development (dτ/dtmax) 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.


OBJECTIVE
The 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/dtmaxduring 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/dtmax, τmax, CT, electromechanical delay (EMD), root-mean squared (RMS) amplitude, peak-to-peak voltage (Vpp), and Q30were calculated.


RESULTS
An ANCOVA showed that τmaxaccounted for all the sex-differences in dτ/dtmax(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/dtmax, 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.


CONCLUSIONS
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.
Electromyographic Kinesiology Laboratory, Faculty of Applied Health Sciences, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON, L2S 3A1, Canada. ginglis@brocku.ca.
J Greig
http://orcid.org/0000-0002-1583-0782
JG
Inglis
Electromyographic Kinesiology Laboratory, Faculty of Applied Health Sciences, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON, L2S 3A1, Canada.
Kyle
K
McIntosh
Electromyographic Kinesiology Laboratory, Faculty of Applied Health Sciences, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON, L2S 3A1, Canada.
David A
DA
Gabriel
D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D012727:Sex Characteristics; D019415:Torque
Contraction time; Electromechanical delay; Muscle activation rate; Muscle fiber conduction velocity; Neural control; Strength testing; Surface electromyography