Sex differences in active tibialis anterior stiffness evaluated using supersonic shear imaging.

This study aimed to evaluate the sex difference in active muscle stiffness of the tibialis anterior muscle (TA) through shear modulus measurements performed using supersonic shear imaging (SSI) technique. Twenty-five women and twenty-one men participated in this study. Joint torque, electromyographic (EMG) activity and shear modulus were measured during two sets of submaximal dorsiflexions performed at 20, 30, 40, 50 and 60% of maximal voluntary contraction (MVC) in a random order. The first set was devoted to the EMG recordings and the second set was devoted to the elastographic measurements. For each set, subjects performed three 5-s trials at each level of submaximal voluntary contraction. Stiffness indexes were calculated as the slopes of the linear regressions established between shear modulus and joint torque (SITORQUE) or estimated TA EMG levels (SIEMG). In the present study, no sex effect was reported for SITORQUE, SIEMG (p=0.76 and p=0.86, respectively), and shear modulus measured at various contraction levels. The results highlight that men and women presented similar TA active stiffness indexes determined using SSI. Regardless of sex, this result suggests similar intrinsic stiffness for the contracting TA.