Abstract
ObjectiveRecent 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.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/dtmax 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/dtmax, 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/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.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.
Highlights
The rate of tension development has received increased attention as a critical aspect of dynamic muscle performance during activities of daily living and sport performance (Aagaard et al 2002; LaRoche et al 2010; Paasuke et al 2001; Pijnapples et al 2008; Schultz et al 1997; Tillin et al 2013)
The current research supports the work by Hannah et al Exp Physiol 97:618–629, (2012) that normalization to maximal voluntary contraction (MVC) in the quadriceps is able to account for all sex-differences in rate of toque development in the lower limb
We suggest that the greater Q30 and reduction in voluntary electromechanical delay (EMD) for females were associated with a different motor unit activity pattern at the onset of muscle contraction
Summary
The rate of tension development has received increased attention as a critical aspect of dynamic muscle performance during activities of daily living (e.g., balance maintenance) and sport performance (Aagaard et al 2002; LaRoche et al 2010; Paasuke et al 2001; Pijnapples et al 2008; Schultz et al 1997; Tillin et al 2013). A number of studies have shown that there is an inextricable link between the ultimate strength of the muscle and its rate of tension development (Andersen and Aagaard 2006; Holtermann et al 2007). Neural factors can play an important role, as training-related increases in the maximal rate of tension development are associated with an increase in muscle activation at the onset of contraction (Van Cutsem et al 1998; Van Cutsem and Duchateau 2005). Inglis et al (2013) recently showed that neural factors play a role in sex-differences in the maximal rate of tension development in the upper limb. The addition of a second variable, the maximum rate of electromyographic (EMG) activity at the onset of contraction (Q30), was able to eliminate statistically significant sex-differences
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