title: Changes in drop-jump landing biomechanics during prolonged intermittent exercise.
abstract: BACKGROUND
  As injury rates rise in the later stages of sporting activities, a better understanding of lower extremity biomechanics in the later phases of gamelike situations may improve training and injury prevention programs.
  
  
  OBJECTIVE
  Lower extremity biomechanics of a drop-jump task (extracted from a principal components analysis) would reveal factors associated with risk of anterior cruciate ligament injury during a 90-minute individualized intermittent exercise protocol (IEP) and for 1 hour following the IEP.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Level 4.
  
  
  METHODS
  Fifty-nine athletes (29 women, 30 men) completed 3 sessions. The first session assessed fitness for an IEP designed to simulate the demands of a soccer match. An experimental session assessed drop-jump biomechanics, after a dynamic warm-up, every 15 minutes during the 90-minute IEP, and for 1 hour following the IEP. A control session with no exercise assessed drop-jump performance at the same intervals.
  
  
  RESULTS
  Two biomechanical factors early in the first half (hip flexion at initial contact and hip loading; ankle loading and knee shear force) decreased at the end of the IEP and into the 60-minute recovery period, while a third factor (knee loading) decreased only during the recovery period (P ≤ 0.05).
  
  
  CONCLUSIONS
  The individualized sport-specific IEP may have more subtle effects on landing biomechanics when compared with short-term, exhaustive fatigue protocols.
  
  
  CONCLUSIONS
  Potentially injurious landing biomechanics may not occur until the later stages of soccer activity.
authors.affiliation: Applied Neuromechanics Research Laboratory, Department of Kinesiology, University of North Carolina at Greensboro, Greensboro, North Carolina.
authors.forename: Randy J
authors.initials: RJ
authors.lastname: Schmitz
authors.affiliation: Portland Timbers Football Club, Portland, Oregon.
authors.forename: John C
authors.initials: JC
authors.lastname: Cone
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of South Florida, Tampa, Florida.
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Tritsch
authors.affiliation: Applied Neuromechanics Research Laboratory, Department of Kinesiology, University of North Carolina at Greensboro, Greensboro, North Carolina.
authors.forename: Michele L
authors.initials: ML
authors.lastname: Pye
authors.affiliation: Department of Kinesiology, California State University, Northridge, California.
authors.forename: Melissa M
authors.initials: MM
authors.lastname: Montgomery
authors.affiliation: Department of Educational Research Methodology, University of North Carolina at Greensboro, Greensboro, North Carolina.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Henson
authors.affiliation: Applied Neuromechanics Research Laboratory, Department of Kinesiology, University of North Carolina at Greensboro, Greensboro, North Carolina.
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Shultz
keywords: anterior cruciate ligament; drop landing; principal components; soccer