title: Effects of knee extension constraint training on knee flexion angle and peak impact ground-reaction force.
abstract: BACKGROUND
  Low compliance with training programs is likely to be one of the major reasons for inconsistency of the data regarding the effectiveness of current anterior cruciate ligament (ACL) injury prevention programs. Training methods that reduce training time and cost could favorably influence the effectiveness of ACL injury prevention programs. A newly designed knee extension constraint training device may serve this purpose.
  
  
  OBJECTIVE
  (1) Knee extension constraint training for 4 weeks would significantly increase the knee flexion angle at the time of peak impact posterior ground-reaction force and decrease peak impact ground-reaction forces during landing of a stop-jump task and a side-cutting task, and (2) the training effects would be retained 4 weeks after completion of the training program.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Twenty-four recreational athletes were randomly assigned to group A or B. Participants in group A played sports without wearing a knee extension constraint device for 4 weeks and then played sports while wearing the device for 4 weeks, while participants in group B underwent a reversed protocol. Both groups were tested at the beginning of week 1 and at the ends of weeks 4 and 8 without wearing the device. Knee joint angles were obtained from 3-dimensional videographic data, while ground-reaction forces were measured simultaneously using force plates. Analyses of variance were performed to determine the training effects and the retention of training effects.
  
  
  RESULTS
  Participants in group A significantly increased knee flexion angles and decreased ground-reaction forces at the end of week 8 (P ≤ .012). Participants in group B significantly increased knee flexion angles and decreased ground-reaction forces at the ends of weeks 4 and 8 (P ≤ .007). However, participants in group B decreased knee flexion angles and increased ground-reaction forces at the end of week 8 in comparison with the end of week 4 (P ≤ .009).
  
  
  CONCLUSIONS
  Knee extension constraint training for 4 weeks significantly altered lower extremity movement patterns and transferred these changes in lower extremity movement patterns to stop-jump and side-cutting tasks in which ACL injuries frequently occur. Training effects were retained 4 weeks after the training was completed but were diminished in magnitude.
  
  
  CONCLUSIONS
  A knee extension constraint device may be a useful training tool in future ACL injury prevention programs to alter movement patterns without extra training time.
authors.affiliation: Bing Yu, Center for Human Movement Science, Division of Physical Therapy, The University of North Carolina at Chapel Hill, Bondurant Hall, CB #7135, Chapel Hill, NC 27599-7135, USA. byu@med.unc.edu.
authors.forename: Hui
authors.initials: H
authors.lastname: Liu
authors.forename: Will
authors.initials: W
authors.lastname: Wu
authors.forename: Wanxiang
authors.initials: W
authors.lastname: Yao
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Spang
authors.forename: R Alexander
authors.initials: RA
authors.lastname: Creighton
authors.forename: William E
authors.initials: WE
authors.lastname: Garrett
authors.forename: Bing
authors.initials: B
authors.lastname: Yu
mesh_terms: D000293:Adolescent; D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena; D001915:Braces; D004867:Equipment Design; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000517:prevention & control*; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D010806:Physical Education and Training; D013177:Sports; D055815:Young Adult
keywords: ACL injury; biomechanics; movement patterns; prevention