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

• Published in: The American journal of sports medicine 2014-03, Vol.42 (3), p.602-609
• Main Authors: Stearns, Kristen M., Powers, Christopher M.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Analysis of Variance; Anterior Cruciate Ligament Injuries; Biomechanical Phenomena - physiology; Biomechanics; Female; Hip joint; Hip Joint - physiology; Human performance; Humans; Isometric Contraction - physiology; Knee Injuries - prevention & control; Knee Joint - physiology; Ligaments; Movement - physiology; Muscle, Skeletal - physiology; Plyometric Exercise; Postural Balance - physiology; Sports medicine; Sports training; Women; Young Adult
• ISSN: 0363-5465; 1552-3365
• DOI: 10.1177/0363546513518410

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° ± 8.5° vs 98.0° ± 10.1°; P < .001) and hip flexion (83.4° ± 7.6° vs 89.9° ± 8.8°; 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° ± 3.3° vs 5.6° ± 3.1°; 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.