title: The association between antagonist hamstring coactivation and episodes of knee joint shifting and buckling.
abstract: OBJECTIVE
  Hamstring coactivation during quadriceps activation is necessary to counteract the quadriceps pull on the tibia, but coactivation can be elevated with symptomatic knee osteoarthritis (OA). To guide rehabilitation to attenuate risk for mobility limitations and falls, this study evaluated whether higher antagonistic open kinetic chain hamstring coactivation is associated with knee joint buckling (sudden loss of support) and shifting (a sensation that the knee might give way).
  
  
  METHODS
  At baseline, median hamstring coactivation was assessed during maximal isokinetic knee extensor strength testing and at baseline and 24-month follow-up, knee buckling and shifting was self-reported. Associations between tertiles of co-activation and knee (1) buckling, (2) shifting and (3) either buckling or shifting were assessed using logistic regression, adjusted for age, sex, knee OA and pain.
  
  
  RESULTS
  1826 participants (1089 women) were included. Mean ± SD age was 61.7 ± 7.7 years, BMI was 30.3 ± 5.5 kg/m(2) and 38.2% of knees had OA. There were no consistent statistically significant associations between hamstring coactivation and ipsilateral prevalent or incident buckling or the combination of buckling and shifting. The odds ratios for incident shifting in the highest in comparison with the lowest tertile of coactivation had similar magnitudes in the combined and medial hamstrings, but only reached statistical significance for lateral hamstring coactivation, OR(95%CI) 1.53 (0.99, 2.36).
  
  
  CONCLUSIONS
  Hamstring coactivation during an open kinetic chain quadriceps exercise was not consistently associated with prevalent or incident self-reported knee buckling or shifting in older adults with or at risk for knee OA.
authors.affiliation: The University of Kansas, Kansas City, KS, United States. Electronic address: segal-research@uiowa.edu.
authors.forename: N A
authors.initials: NA
authors.lastname: Segal
authors.affiliation: University of California San Francisco, San Francisco, CA, United States. Electronic address: mnevitt@psg.ucsf.edu.
authors.forename: M C
authors.initials: MC
authors.lastname: Nevitt
authors.affiliation: The University of Iowa, Iowa City, IA, United States. Electronic address: robert-welborn@uiowa.edu.
authors.forename: R D
authors.initials: RD
authors.lastname: Welborn
authors.affiliation: Boston University School of Medicine, Boston, MA, United States; University of Massachusetts Medical School, Worcester, MA, United States. Electronic address: UyenSa.Nguyen@umassmed.edu.
authors.forename: U-S D T
authors.initials: US
authors.lastname: Nguyen
authors.affiliation: Boston University School of Medicine, Boston, MA, United States. Electronic address: niujp@bu.edu.
authors.forename: J
authors.initials: J
authors.lastname: Niu
authors.affiliation: University of Alabama at Birmingham, Birmingham, AL, United States. Electronic address: celewis@uabmc.edu.
authors.forename: C E
authors.initials: CE
authors.lastname: Lewis
authors.affiliation: Boston University School of Medicine, Boston, MA, United States. Electronic address: dfelson@bu.edu.
authors.forename: D T
authors.initials: DT
authors.lastname: Felson
authors.affiliation: The University of Iowa, Iowa City, IA, United States. Electronic address: laura-freylaw@uiowa.edu.
authors.forename: L
authors.initials: L
authors.lastname: Frey-Law
mesh_terms: D000368:Aged; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000209:etiology / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D020370:Osteoarthritis, Knee / Q000150:complications / Q000503:physiopathology*; D012307:Risk Factors; D013710:Tendons / Q000503:physiopathology*
keywords: Epidemiology; Knee; Muscle activation; Osteoarthritis