title: The effect of thigh muscle activity on anterior knee laxity in the uninjured and anterior cruciate ligament-injured knee.
abstract: OBJECTIVE
  The main purpose of this study was to describe the nature of the relationship between hamstring muscle activity and anterior knee laxity.
  
  
  METHODS
  This was a cross-sectional study. Anterior knee laxity was measured at 133N and manual maximal forces using the KT2000 knee arthrometer, in 8 ACL-injured and 13 uninjured individuals. Electromyographic activity of the lateral hamstrings was measured during laxity testing. Subjects contracted the hamstrings during anterior knee laxity testing at eight predetermined levels of maximal voluntary isometric contraction.
  
  
  RESULTS
  Volitional contraction of the lateral hamstrings reduced anterior knee laxity logarithmically for both the 133N and manual maximal tests in both the ACL-injured and uninjured knees. A simple linear regression model, with the log of percentage of maximum lateral hamstrings activity as the sole predictor, explained approximately 70-80% of the variation in anterior knee laxity. Both ACL-injured and uninjured subjects reduced anterior knee laxity at the same rate with increases in muscle activity. However, initial lateral hamstrings muscle activity had a greater effect on percentage anterior knee laxity scores in the ACL-injured as compared to the uninjured knee.
  
  
  CONCLUSIONS
  Lateral hamstrings activity reduces anterior knee laxity in a nonlinear manner, whereby the initial lower level of activation produces the greatest change in anterior knee laxity. Therefore, hamstrings muscle activity must be monitored during anterior knee laxity testing.
authors.affiliation: Academic Department of Physiotherapy, School of Medicine, King's College London, London, UK.
authors.forename: Massimo G
authors.initials: MG
authors.lastname: Barcellona
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Morrissey
authors.forename: Peter
authors.initials: P
authors.lastname: Milligan
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Amis
mesh_terms: D000328:Adult; D016118:Anterior Cruciate Ligament / Q000503:physiopathology; D000070598:Anterior Cruciate Ligament Injuries; D003430:Cross-Sectional Studies; D004576:Electromyography; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007717:Knee / Q000503:physiopathology*; D007718:Knee Injuries / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology*; D013848:Thigh; D055815:Young Adult