title: Sex Differences in Knee Flexion Angle During a Rapid Change of Direction While Running.
abstract: BACKGROUND
  Females experience greater overall rates of athletic anterior cruciate ligament (ACL) injury than males. The specific mechanisms of the predisposition remain unclear.
  
  
  OBJECTIVE
  Modeling of knee kinematics has shown that the more extended the knee joint, the greater the strain on the ACL. The authors hypothesized that female athletes would have a lesser degree of knee flexion than male athletes at initial ground contact while performing change-of-direction cutting maneuvers.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Twenty female and 20 male high school soccer athletes with at least 1 year of experience were recruited for the study. Athletes were excluded if they had a history of any major lower limb injury or current knee pain causing a reduction in training and/or competition. Reflective markers were attached at the greater trochanter of the femur, the lateral epicondyle of the knee, and the lateral malleolus of the ankle to enable motion capture. Each athlete performed 6 change-of-direction maneuvers in random order in front of 2 cameras. Multiple regression analysis was used to determine differences between the sexes from the motion data captured; P < .05 defined significance.
  
  
  RESULTS
  Statistically significant differences existed in knee flexion angles between male and female participants at the 90° and 135° cutting angles. At 90°, males and females showed initial contact knee flexion angles (mean ± SD) of 39.0° ± 6.8° and 29.3° ± 6.2°, respectively (P < .0001), and mean maximum flexion angles of 56.4° ± 6.9° and 49.7° ± 7.0°, respectively (P = .0036). At 135°, males and females showed mean initial contact knee flexion angles of 36.8° ± 7.9° and 29.7° ± 7.8°, respectively (P = .0053), and mean maximum flexion angles of 60.7° ± 8.1° and 51.6° ± 9.4°, respectively (P = .0017).
  
  
  CONCLUSIONS
  The research conducted is intended to foster an awareness of injury disposition in female athletes and guide future endeavors to develop, test, and implement a proactive approach in lowering female noncontact athletic ACL injury rates. This project adds to the literature as wider side-cut maneuvers (≥90°) were studied, as compared with previous studies using small side-cut angles (<90°), offering a model for alternative sports actions.
authors.affiliation: University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Sheu
authors.affiliation: University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Gray
authors.affiliation: University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: David
authors.initials: D
authors.lastname: Brown
authors.affiliation: University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Smith
keywords: ACL; anterior cruciate ligament; flexion; injury; kinematics; knee; motion analysis; sex; soccer