title: The effect of sex and fatigue on lower limb kinematics, kinetics, and muscle activity during unanticipated side-step cutting.
abstract: OBJECTIVE
  To determine how sex and fatigue affect lower limb kinematics, kinetics, and muscle activity during unanticipated side-step cutting.
  
  
  METHODS
  Twenty-three physically active subjects (men 11, women 12) performed 10 successful trials of cutting manoeuvres each to either side under unanticipated conditions in response to 2 light emitting diodes before and after fatigue conditions. Data were analysed and compared regarding sex and fatigue conditions using two-way repeated measures analysis of variance.
  
  
  RESULTS
  After fatigue-inducing exercise, women demonstrated larger impulses of ground reaction force (IGRF) during the first 50 ms (2.4 ± 0.8 vs. 2.1 ± 0.9, P < 0.05) than did men. Significant primary effects of sex indicated that women showed a smaller hip flexion angle at initial contact (40.4 ± 6.9° vs. 49.7 ± 9.1°, P < 0.05) and at maximum flexion angle (41.3 ± 7.7° vs. 51.4 ± 9.0°, P < 0.05) compared with men. Significant primary effects of fatigue were observed in the gluteus maximus muscle during 50 ms before initial contact (+21.5 ± 48.3 %, P < 0.05) and in the semimembranosus muscle during 50 ms before initial contact (-6.2 ± 20.1 %, P < 0.05) and the first 50 ms of side-step cutting (-7.9 ± 26.6 %, P < 0.05).
  
  
  CONCLUSIONS
  Our results suggest that sex differences, especially larger IGRF in a fatigue state combined with less hip flexion angle, lead to women having a higher risk for anterior cruciate ligament (ACL) injury. These findings may contribute to understanding the underlying mechanism of injury and development of preventive exercises against ACL injury.
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Kawara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan, iguchi.junta.86a@st.kyoto-u.ac.jp.
authors.forename: Junta
authors.initials: J
authors.lastname: Iguchi
authors.forename: Hiroshige
authors.initials: H
authors.lastname: Tateuchi
authors.forename: Masashi
authors.initials: M
authors.lastname: Taniguchi
authors.forename: Noriaki
authors.initials: N
authors.lastname: Ichihashi
mesh_terms: D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D056352:Athletes; D001696:Biomechanical Phenomena; D004576:Electromyography; D015444:Exercise / Q000502:physiology; D005260:Female; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D007718:Knee Injuries / Q000453:epidemiology / Q000503:physiopathology*; D007719:Knee Joint / Q000502:physiology*; D007866:Leg / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D016059:Range of Motion, Articular; D012737:Sex Factors; D013177:Sports / Q000502:physiology*; D013647:Task Performance and Analysis; D055815:Young Adult