Neuromuscular Response Characteristics in Men and Women After Knee Perturbation in a Single-Leg, Weight-Bearing Stance.

OBJECTIVE: We examined whether muscle response times and activation patterns in the lower extremity differed between men and women in response to a rotational knee perturbation while standing in a single-leg, weight-bearing stance. DESIGN AND SETTING: We used a lower extremity perturbation device to produce a sudden, forward, and either internal or external rotation moment of the trunk and femur relative to the weight-bearing tibia. Subjects completed 10 trials of both internal and external rotation perturbation; the first 5 acceptable trials were averaged and used for data analysis. Two separate, repeated-measures analyses of variance were used to compare myoelectric response times and activation patterns between men and women for both internal and external rotation perturbation. SUBJECTS: Thirty-two female (19 lacrosse, 13 soccer) and 32 male (lacrosse) healthy intercollegiate athletes participated in the study. MEASUREMENTS: We used surface electromyography to record long latency reflex times of the medial and lateral quadriceps, hamstring, and gastrocnemius muscles. RESULTS: Women responded faster than men, primarily due to a shorter latency in quadriceps activation. However, men and women exhibited no difference in muscle-recruitment order. CONCLUSIONS: Although men and women demonstrated similar muscle-recruitment patterns to an imposed lower extremity perturbation, women tended to activate their quadriceps earlier than men. Whether this earlier quadriceps activation diminishes the ability of the hamstrings to adequately stabilize the knee joint or subjects the anterior cruciate ligament to greater risk of injury is still unknown and requires further study. Furthermore, although surface electromyography and measurement of myoelectric response times are useful in evaluating the timing, activation order, and coactivity patterns of the knee musculature, future studies should evaluate sex differences across the complete response continuum, including measures of intrinsic muscle stiffness, electromechanical delay, and time to force production.