Muscle Strength and Qualitative Jump-landing Differences in Male and Female Military Cadets: the Jump-acl Study.

Recent studies have focused on gender differences in movement patterns as risk factors for ACL injury. Understanding intrinsic and extrinsic factors which contribute to movement patterns is critical to ACL injury prevention efforts. Isometric lower-extremity muscular strength, anthropometrics, and jump-landing technique were analyzed for 2,753 cadets (1,046 female, 1,707 male) from the U.S. Air Force, Military and Naval Academies. Jump-landings were evaluated using the Landing Error Scoring System (LESS), a valid qualitative movement screening tool. We hypothesized that distinct anthropometric factors (Q-angle, navicular drop, bodyweight) and muscle strength would predict poor jump-landing technique in males versus females, and that female cadets would have higher scores (more errors) on a qualitative movement screen (LESS) than males. Mean LESS scores were significantly higher in female (5.34 ± 1.51) versus male (4.65 ± 1.69) cadets (P<.001). Qualitative movement scores were analyzed using factor analyses, yielding five factors, or "patterns", contributing to poor landing technique. Females were significantly more likely to have poor technique due to landing with less hip and knee flexion at initial contact (P<.001), more knee valgus with wider landing stance (P<.001), and less flexion displacement over the entire landing (P<.001). Males were more likely to have poor technique due to landing toe-out (P<.001), with heels first, and with an asymmetric foot landing (P<.001). Many of the identified factor patterns have been previously proposed to contribute to ACL injury risk. However, univariate and multivariate analyses of muscular strength and anthropometric factors did not strongly predict LESS scores for either gender, suggesting that changing an athlete's alignment, BMI, or muscle strength may not directly improve his or her movement patterns.