Improvements in Hip Muscle Performance Result in Increased Use of the Hip Extensors and Abductors During a Landing Task

Background: Impaired hip muscle performance has been implicated as a contributing factor to the increased risk of anterior cruciate ligament (ACL) injury in women. Purpose: To determine the influence of a hip-focused training program on lower extremity biomechanics during a drop-jump task. Study Design: Descriptive laboratory study. Methods: Twenty-one recreationally active women (18-25 years of age) participated in a 4-week training program consisting of hip-focused plyometric and balance perturbation exercises (3 times/wk, 30 min/session). Maximum isometric strength of the hip extensors, hip abductors, and knee extensors was assessed, along with lower extremity biomechanics during a drop-jump task. All assessments were performed within 5 days of initiation and completion of the training program. Results: After training, subjects demonstrated significantly greater maximum isometric strength of the hip extensors (2.87 +/- 0.7 vs 3.11 +/- 0.7 N.m/kg; P < .01) and hip abductors (2.08 +/- 0.7 vs 2.23 +/- 0.07 N.m/kg; P = .004). No significant difference in knee extensor strength was observed. After training, subjects landed with significantly greater peak knee flexion (94.0 degrees +/- 8.5 degrees vs 98.0 degrees +/- 10.1 degrees; P < .001) and hip flexion (83.4 degrees +/- 7.6 degrees vs 89.9 degrees +/- 8.8 degrees; P = .008) and a lower knee/hip extensor moment ratio (1.33 +/- 0.6 vs 0.99 +/- 0.3; P = .001). In addition, subjects demonstrated significantly lower peak knee abduction angles (6.8 degrees +/- 3.3 degrees vs 5.6 degrees +/- 3.1 degrees; P = .04) and average knee adductor moments (0.06 +/- 0.1 vs -0.02 +/- 0.1 N.m/kg; P < .001). Conclusion: Changes in lower extremity biomechanics consistent with decreased risk for ACL injury were observed after participation in a hip-focused training program. Clinical Relevance: The study results suggest that ACL injury prevention programs targeting hip muscle performance may be important in mitigating biomechanical risk factors associated with ACL injury in women.