Despite years of research, females continue to have a higher incidence of non-contact ACL injuries. One of the major findings of this research is that males and females perform certain tasks, such as, cutting, landing, and single-leg squatting, differently. In particular, females tend to move the knee into a more valgus position; a motion putting the ACL at risk for injury. Yet the underlying spinal control mechanisms modulating this motion are unknown. Additionally, the mechanisms regulating the ability to rapidly initiate and produce maximal torque are also unknown. Therefore, the purpose was to: 1) determine if the sexes modulate spinal control differently, 2) examine the contributions of spinal control mechanisms to valgus knee motion, and 3) identify contributions of spinal control to the ability to rapidly produce force. The spinal control variables were the first derivative of the Hoffmann (H)-reflex, the first derivative of extrinsic pre-synaptic inhibition (EPI), the first derivative of intrinsic pre-synaptic inhibition (IPI), recurrent inhibition (RI), and V-waves. To assess the neuromuscular system’s ability to rapidly activate, rate of torque development (RTD) and electromechanical delay (EMD) were measured. Lastly, valgus motion was determined by the frontal plane projection angle (FPPA). The results reveal males and females do modulate spinal control differently; specifically males had an increased RTD, which is the slope of the torque-time curve, and increased RI, which is a post-synaptic regulator of torque output. However, the spinal control mechanisms did not significantly contribute to FPPA at the knee. EMD which is the time lag from muscle activity to torque production was significantly predicted by the spinal control mechanisms. Specifically, EPI, a modulator of afferent inflow from peripheral and descending sources, IPI, a regulator of Ia afferent inflow, and sex significantly contributed to EMD. Lastly, the spinal control mechanisms significantly contributed to RTD. Specifically, IPI, sex, and V-waves, a measure of supraspinal drive, all significantly contributed to RTD. / Graduation date: 2009