The independent and interactive effects of navicular drop and quadriceps angle on neuromuscular responses to a weight-bearing perturbation.

CONTEXT Little is known about the effects of static alignment on neuromuscular control of the knee during dynamic motion. OBJECTIVE To evaluate the isolated and combined effects of quadriceps angle (QA) and navicular drop (ND) on neuromuscular responses to a weight-bearing perturbation. DESIGN Mixed-model, repeated-measures design. SETTING Sports medicine and athletic training research laboratory. PATIENTS OR OTHER PARTICIPANTS Seventy-nine National Collegiate Athletic Association Division I collegiate female athletes, classified with below-average ND and QA (LND-LQA); below-average ND and above-average QA (LND-HQA); above-average ND and below-average QA (HND-LQA); or above-average ND and QA (HND-HQA). INTERVENTION(S) A lower extremity perturbation device produced a forward and either internal or external rotation of the trunk and femur on the weight-bearing tibia to evoke a reflex response. MAIN OUTCOME MEASURE(S) Neuromuscular responses were examined in the quadriceps, hamstrings, and gastrocnemius muscles: preperturbation amplitude 50 milliseconds before the perturbation, reflex time, and postperturbation amplitude 150 milliseconds immediately postperturbation. RESULTS Navicular drop had the greatest effect on preperturbation amplitude of the lateral hamstrings and postperturbation amplitude of all muscles, with greater activation amplitude noted in subjects in the HND classifications. Quadriceps angle primarily affected reflex time of the quadriceps; in subjects with LQA, reflex time was faster for internal rotation than external rotation perturbations. The interaction between ND and QA had the greatest effect on reflex time of the lateral hamstrings. For internal rotation perturbations, subjects in the LND classifications had faster reflex times in the lateral hamstrings if they had HQA values rather than LQA values. With external rotation perturbations, HND-LQA subjects had slower reflex times than those in all other alignment classifications. CONCLUSIONS Navicular drop and QA have both independent and interactive effects on neuromuscular responses to a weight-bearing, rotational perturbation. These interactive effects highlight the importance of considering the entire lower extremity posture rather than a single alignment characteristic, given the potential for one alignment factor to compensate for or interact with another.