Evidence of gender-specific motor templates to resist valgus loading at the knee

Gender differences in neuromuscular control of the lower extremity may contribute to increased injury risk in females, but the neurophysiological mechanisms underlying these differences remain unclear. In this study, we sought to explore the effect of gender on volitional and reflex neuromuscular responses to a rapid valgus perturbation at the knee applied under "intervene" and "do not intervene" conditions. Multiple 7 degrees ramp-and-hold valgus perturbations were applied at the neutrally extended knee of 12 male and 12 female healthy subjects, while surface electromyography over the quadriceps and hamstrings recorded the neuromuscular response. Volitional responses did not vary between groups, perhaps reflecting the relative novelty of the loading direction. However, reflex responses observed under the "do not intervene" paradigm did vary by gender. Males demonstrated much more frequent and consistent reflex muscle activation than females. Moreover, muscle activation patterns were gender-specific. Diminished responses in female subjects may indicate that the position-based valgus perturbation did not produce the necessary mechanical stimulus to elicit reflexes. These gender differences in reflex control of the knee provide new insight into the control of frontal-plane knee joint movement and loading and may elucidate the neuromechanical underpinnings associated with neuromuscular control.