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Gender Differences in Lower Extremity Landing Mechanics Caused by Neuromuscular Fatigue

Thomas W. Kernozek, PhD^,,*, Michael R. Torry, PhD and Mark Iwasaki, MSPT

From the University of Wisconsin–La Crosse, Department of Health Professions, Physical Therapy Program, La Crosse, Wisconsin, Gundersen Lutheran Sports Medicine, La Crosse, Wisconsin, and the Steadman Hawkins Research Foundation, Vail, Colorado

^* Address correspondence to Thomas W. Kernozek, PhD, La Crosse Institute for Movement Science, Department of Health Professions, University of Wisconsin–La Crosse, 1300 Badger Street, La Crosse, WI 54601 (e-mail: kernozek.thom{at}uwlax.edu).

Background: Neuromuscular fatigue has been suggested as an extrinsic factor in the mechanism of noncontact anterior cruciate ligament injury in both genders.

Purpose: To determine and describe the lower extremity kinematic and kinetic differences caused by neuromuscular fatigue during drop landings and compare changes between age- and skill-matched male and female athletes.

Methods: Inverse dynamic solutions estimated lower extremity flexion-extension and varus-valgus kinematics and kinetics for 14 female and 16 male athletes performing a single-legged 50-cm drop landing. Subjects performed landings prefatigue and postfatigue with fatigue induced via a parallel squat exercise (60% of 1 repetition maximum) until failure. A mixed-model, repeated-measures analysis of variance (fatigue * gender) was performed on select kinematic and kinetic variables.

Results: Neuromuscular fatigue caused men and women to land with more hip flexion (main effect fatigue, P = .012; main effect gender, P = .001). Men exhibited greater peak knee flexion angles postfatigue; women did not alter knee flexion (fatigue * gender, P = .028). Men exhibited larger peak knee varus angles irrespective of fatigue (main effect gender, P = .039; main effect fatigue, P = .127; fatigue * gender, P = .153); women demonstrated larger peak valgus angles overall (main effects gender, P = .009). There were no changes with fatigue (main effect fatigue, P = .127) or a different response due to fatigue with gender (fatigue * gender, P = .091). Women exhibited greater knee anterior shear force postfatigue (fatigue * gender, P = .010). Men and women exhibited lower knee extension moments (main effect fatigue, P = .000; main effect gender, P = .927; fatigue * gender, P = .309) and abduction moments (main effect fatigue, P = .014; main effect gender, P = .670; fatigue * gender, P = .191).

Conclusion: Neuromuscular fatigue caused significant alterations in women that may be indicative of the noncontact anterior cruciate ligament injury mechanisms.

Clinical Relevance: Current noncontact anterior cruciate ligament prevention programs should incorporate a fatigue component to help minimize the deleterious effects of neuromuscular fatigue on landing mechanics.

Key Words: anterior cruciate ligament (ACL) • neuromuscular fatigue • knee injury • gender • biomechanics