Running Head: Spinal and Supraspinal Predictors of RTD Spinal and Supraspinal Motor Control Predictors of Rate of Torque Development

During explosive movements and potentially injurious situations the ability to rapidly generate torque is critical. Previous research has suggested different phases of rate of torque development (RTD) are differentiately controlled. However, the extent to which supraspinal and spinal mechanisms predict RTD at different time intervals is unknown. RTD of the plantarflexors across various phases of contraction (i.e., 0-25ms, 0-50ms, 0-100ms, 0-150ms, 0-200ms, and 0-250ms) was measured in 37 participants. The following predictor variables were also measured: (a) gain of the resting soleus H-reflex recruitment curve, (b) gain of the resting homonymous post-activation depression recruitment curve, (c) gain of the GABAergic pre-synaptic inhibition recruitment curve, (d) the level of post-synaptic recurrent inhibition at rest, (e) level of supraspinal drive assessed by measuring V waves, and (f) the gain of the resting soleus M Wave. Stepwise regression analyses were used to determine which variables significantly predicted allometrically scaled RTD. The analyses indicated that supraspinal drive was the dominant predictor of RTD across all phases. Additionally, recurrent inhibition predicted RTD in all of the t ime intervals except 0-150 ms. These results demonstrate the importance of supraspinal drive and recurrent inhibition to RTD.