Spinal motor control differences between the sexes.

Activity-related knee joint dysfunction is more prevalent in females than males. One explanation for the discrepancy is differences in movement patterns between the sexes. However, the underlying mechanisms responsible for these differences remain unidentified. This study tested spinal motor control mechanisms influencing motor neuron pool output and subsequent muscle activation in 17 males and 17 females. The following variables were assessed at the soleus: the gain of the unconditioned H-reflex, gain of both intrinsic pre-synaptic inhibition (IPI) and extrinsic pre-synaptic inhibition (EPI), the level of recurrent inhibition (RI), the level of supraspinal drive determined by the ratio of the Vmax:Mmax (V-wave), electromechanical delay (EMD) and the rate of force development (RFD). The Wilks Lambda multivariate test of overall differences among groups was significant (p = 0.031). Univariate between-subjects tests revealed males had greater RI (p = 0.042). However, the sexes did not differ on any of the other variables tested. In conclusion, the sexes differ on modulation of spinal motor control. Specifically, RI, a post-synaptic regulator of force output, was greater in males.