title: Changes in fatigue, multiplanar knee laxity, and landing biomechanics during intermittent exercise.
abstract: BACKGROUND
  Knee laxity increases during exercise. However, no one, to our knowledge, has examined whether these increases contribute to higher-risk landing biomechanics during prolonged, fatiguing exercise.
  
  
  OBJECTIVE
  To examine associations between changes in fatigue (measured as sprint time [SPTIME]), multiplanar knee laxity (anterior-posterior [APLAX], varus-valgus [VVLAX] knee laxity, and internal-external rotation [IERLAX]) knee laxity and landing biomechanics during prolonged, intermittent exercise.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Laboratory and gymnasium.
  
  
  METHODS
  A total of 30 male (age = 20.3 ± 2.0 years, height = 1.79 ± 0.05 m, mass = 75.2 ± 7.2 kg) and 29 female (age = 20.5 ± 2.3 years, height = 1.67 ± 0.08 m, mass = 61.8 ± 9.0 kg) competitive athletes.
  
  
  METHODS
  A 90-minute intermittent exercise protocol (IEP) designed to simulate the physiologic and biomechanical demands of a soccer match.
  
  
  METHODS
  We measured SPTIME, APLAX, and landing biomechanics before and after warm-up, every 15 minutes during the IEP, and every 15 minutes for 1 hour after the IEP. We measured VVLAX and IERLAX before and after the warm-up, at 45 and 90 minutes during the IEP, and at 30 minutes after the IEP. We used hierarchical linear modeling to examine associations between exercise-related changes in SPTIME and knee laxity with exercise-related changes in landing biomechanics while controlling for initial (before warm-up) knee laxity.
  
  
  RESULTS
  We found that SPTIME had a more global effect on landing biomechanics in women than in men, resulting in a more upright landing and a reduction in landing forces and out-of-plane motions about the knee. As APLAX increased with exercise, women increased their knee internal-rotation motion (P = .02), and men increased their hip-flexion motion and energy-absorption (P = .006) and knee-extensor loads (P = .04). As VVLAX and IERLAX increased, women went through greater knee-valgus motion and dorsiflexion and absorbed more energy at the knee (P ≤ .05), whereas men were positioned in greater hip external and knee internal rotation and knee valgus throughout the landing (P = .03). The observed fatigue- and laxity-related changes in landing biomechanics during exercise often depended on initial knee laxity.
  
  
  CONCLUSIONS
  Both exercise-related changes in fatigue and knee laxity were associated with higher-risk landing biomechanics during prolonged exercise. These relationships were more pronounced in participants with greater initial knee laxity.
authors: Applied Neuromechanics Research Laboratory, Department of Kinesiology, University of North Carolina at Greensboro;
authors: Sandra J
authors: SJ
authors: Shultz
authors: Randy J
authors: RJ
authors: Schmitz
authors: John R
authors: JR
authors: Cone
authors: Robert A
authors: RA
authors: Henson
authors: Melissa M
authors: MM
authors: Montgomery
authors: Michele L
authors: ML
authors: Pye
authors: Amanda J
authors: AJ
authors: Tritsch
mesh_terms: D016118:Anterior Cruciate Ligament / Q000502:physiology; D001696:Biomechanical Phenomena; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis / Q000503:physiopathology; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D016059:Range of Motion, Articular; D012399:Rotation; D012916:Soccer / Q000502:physiology; D013997:Time Factors; D055815:Young Adult
keywords: anterior cruciate ligament injuries; joints; risk factors; soccer