Surface electromyography (sEMG) has demonstrated that the electrophysiological component of the patella stretch reflex (PR) for the vastus lateralis (VL) in human females is significantly faster than that for males; an effect that cannot be accounted for by differences in stature between the two genders (Vickery and Smith 2013). One possible explanation for this difference is that the nerve conduction velocities for the afferent and efferent pathways of this mono synaptic spinal reflex is sexually dimorphic. We have investigated the later possibility. Caucasian subjects of both genders with no known neurophysiological deficits or injury were recruited from the student population (Age range 20-22). Alpha-motor neuron conduction velocity (MNCV) was determined indirectly by the measurement of the latencies to the appearance of the muscle compound action potentials (MCAP) that are evoked in the VL at various distances down the muscle, during the PR, due to alpha-motor nerve innervation. The PR was elicited by a constant energy tap of 125 mJ delivered at 0.2 Hz via a pendulum hammer. The MCAPs were measured using sEMG via an extracellular 7 electrode array in a linear arrangement, interelectrode distance 30mm, attached along the long axis of the VL. The array was centred on the bipolar measurement positions recommended by SENIAM (Freriks et al 1999). All values are quoted as mean ± S.E.M.In 12 female, and 14 male subjects, the latency to the MCAP was linearly and positively correlated with the proximal distance (p<0.05 Pearson) and on average occurred 1.8 ± 0.5 ms earlier in females (p<0.005, Unpaired t-test). Linear regression yielded a mean MNCV that was 9.8±4.4 m s-1 faster in the females (64.9±2.6 m s-1 ) than in the males (54.0±3.4 m s-1 ) (p<0.05, Unpaired t-test). A simple linear model, in which all electrophysiological events prior to post-spinal excitation of L4 alpha-motorneurons were lumped together, and which was required to be 0.5±0.05 ms slower in males, readily accounted for the relationship between the gender difference in latency and proximal electrode distance when the differences in the motor nerve conduction path length and its associated MNCV between the two genders were considered. A model in which the genders had the same MNCV could not describe the gender-specific change in PR latency with conduction distance. In conclusion the faster latency for the VL component of the patella stretch reflex in human females can be partly, if not entirely, accounted for by gender differences in the alpha-motor neuron conduction velocity. Whether the later arises through differences in internodal distance, extent of myelination, or ion channel density remains unknown.