title: Limited hip and knee flexion during landing is associated with increased frontal plane knee motion and moments.
abstract: BACKGROUND
  It has been proposed that female athletes who limit knee and hip flexion during athletic tasks rely more on the passive restraints in the frontal plane to deceleration their body center of mass. This biomechanical pattern is thought to increase the risk for anterior cruciate ligament injury. To date, the relationship between sagittal plane kinematics and frontal plane knee motion and moments has not been explored.
  
  
  METHODS
  Subjects consisted of 58 female club soccer players (age range: 11-20 years) with no history of knee injury. Kinematics, ground reaction forces, and surface electromyography were collected while each subject performed a drop landing task. Subjects were divided into two groups based on combined sagittal plane knee and hip flexion angles during the deceleration phase of landing (high flexion and low flexion).
  
  
  RESULTS
  Subjects in the low flexion group demonstrated increased knee valgus angles (P=0.02, effect size 0.27), increased knee adductor moments (P=0.03, effect size 0.24), decreased energy absorption at the knee and hip (P=0.02, effect size 0.25; and P<0.001, effect size 0.59), and increased vastus lateralis EMG when compared to subjects in the high flexion group (P=0.005, effect size 0.35).
  
  
  CONCLUSIONS
  Female athletes with limited sagittal plane motion during landing exhibit a biomechanical profile that may put these individuals at greater risk for anterior cruciate ligament injury.
authors.affiliation: Jacquelin Perry Musculoskeletal Biomechanics Research Laboratory, Division of Biokinesiology and Physical Therapy, University of Southern California, 1540 East Alcazar Street, Los Angeles, CA 90033, USA. cpollard@usc.edu
authors.forename: Christine D
authors.initials: CD
authors.lastname: Pollard
authors.forename: Susan M
authors.initials: SM
authors.lastname: Sigward
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Powers
mesh_terms: D000293:Adolescent; D002648:Child; D003198:Computer Simulation; D005260:Female; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D012916:Soccer / Q000502:physiology*; D013647:Task Performance and Analysis; D055815:Young Adult