Females Recruit Quadriceps Faster Than Males at Multiple Knee Flexion Angles Following a Weight-Bearing Rotary Perturbation

Objective: To compare the effect of knee angle on muscle response times and neuromuscular recruitment patterns between sexes following a perturbation in single leg stance at 10°, 20°, and 30°. We hypothesized that response times would be faster at lesser knee flexion angles and that females would recruit their quadriceps faster than males at all angles. Design: A repeated-measures design. Setting: Motion analysis laboratory. Participants: Twenty (10 female; 10 male) healthy, recreationally active volunteers. Interventions: A rotary perturbation in single leg stance. Outcome Measurements: Response times of the medial and lateral quadriceps, hamstrings, and gastrocnemius. Results: There was a trend toward faster response times for all muscles closer toward extension. A consistent neuromuscular recruitment pattern for both males and females was evident for each knee angle tested. Females, however, contracted their quadriceps faster than males at all knee flexion angles. Conclusions: Small changes in knee angle near extension do not alter muscle response times and hence neuromuscular recruitment patterns in males and females. Regardless of knee flexion angle, following a perturbation in single leg stance, females contract their quadriceps faster than males. Clinical Relevance: Earlier contraction of the quadriceps in females may increase anterior tibial translation and hence anterior cruciate ligament strain, thereby heightening injury risk.