title: Activation deficits do not limit quadriceps strength training gains in patients after total knee arthroplasty.
abstract: OBJECTIVE
  Patients after total knee arthroplasty (TKA) are known to exhibit deficits in quadriceps muscle activation. The purpose of this study was to determine if quadriceps activation levels in patients after TKA at the beginning of rehabilitation would influence quadriceps strength after rehabilitation.
  
  
  METHODS
  A secondary analysis of data from a prospective, randomized, longitudinal clinical trial.
  
  
  METHODS
  Institutional clinic and research laboratory.
  
  
  METHODS
  Patients who underwent unilateral TKA (Men= 102; Female= 84).
  
  
  RESULTS
  Voluntary activation of the quadriceps during maximal voluntary isometric contractions (MVIC) was measured using the central activation ratio (CAR). Hierarchical multivariate regression analysis was used to determine if CAR prior to treatment could predict MVIC after the strength training intervention.
  
  
  RESULTS
  After controlling for age, sex, and initial strength levels (R(2)= 0.548; p<0.001), the predictability of quadriceps strength after the 6-week intervention did not change when pain during MVIC (R(2)= 0.551; p= 0.317) and pre-rehabilitation activation levels (R(2)= 0.551; p= 0.818) were introduced into the regression.
  
  
  CONCLUSIONS
  Initial quadriceps activation levels, for patients who underwent TKA, did not predict the quadriceps strength following a strength training intervention. Therefore, deficits in voluntarily activation post-operatively should not be considered as a rate-limiting factor in recovering quadriceps strength after TKA.
  
  
  METHODS
  Retrospective cohort study. Level IIb.
authors.affiliation: University of Delaware, Newark DE, USA.
authors.forename: Adam R
authors.initials: AR
authors.lastname: Marmon
authors.affiliation: University of Delaware, Newark DE, USA.
authors.forename: Lynn
authors.initials: L
authors.lastname: Snyder-Mackler
keywords: Central activation ration; knee extensors; knee replacement