title: Changes in voluntary quadriceps activation predict changes in muscle strength and gait biomechanics following knee joint effusion.
abstract: BACKGROUND
  It has been hypothesized that arthrogenic muscle inhibition is responsible for altering physical function following knee injury. The association between the onset of arthrogenic muscle inhibition, measured using voluntary quadriceps activation, and changes in muscle strength and gait biomechanics are unknown.
  
  
  METHODS
  Outcomes were collected before and following a 60 ml experimental knee effusion in eighteen healthy participants. Voluntary quadriceps activation was the predictor variable, while the criterion variable included, maximal voluntary isometric strength, peak knee flexion angle, peak internal knee extension moment, and peak vertical ground reaction forces during the first half of stance phase upon stair descent. Percent change scores (Δ) were imputed into linear regression equations to determine associations between predictor and criterion variables.
  
  
  RESULTS
  The variance in Δ voluntary quadriceps activation significantly predicted 87% the variance in the Δ strength (R(2)=0.87, P<0.001; Δ strength=-2.15+1.77Δ voluntary quadriceps activation) and 25% of the Δ vertical ground reaction force following effusion (R(2)=0.25, P=0.04; Δ vertical ground reaction force=-6.1+0.57 Δ voluntary quadriceps activation). After accounting for Δ knee flexion angle, Δ voluntary quadriceps activation predicted an additional 29% (Δ R(2)=0.29, P=0.007) of the variance in the Δ knee extension moment (R(2)=0.54, P=0.003, Δ knee extension moment=-10.79+0.74Δ knee flexion angle+1.64Δ voluntary quadriceps activation) following knee effusion.
  
  
  CONCLUSIONS
  Immediate quadriceps activation deficits following joint effusion result in immediate alterations in muscle strength, knee extensor moment and vertical ground reaction force during gait.
authors: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States. Electronic address: brian@unc.edu.
authors: Brian
authors: B
authors: Pietrosimone
authors: Department of Kinesiology, University of Toledo, Toledo, OH, United States.
authors: Adam S
authors: AS
authors: Lepley
authors: Department of Kinesiology, University of Toledo, Toledo, OH, United States.
authors: Amanda M
authors: AM
authors: Murray
authors: Department of Kinesiology, University of Toledo, Toledo, OH, United States.
authors: Abbey C
authors: AC
authors: Thomas
authors: Department of Family Medicine, University of Toledo, Toledo, OH, United States.
authors: Nael O
authors: NO
authors: Bahhur
authors: Department of Biostatistics, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States.
authors: Todd A
authors: TA
authors: Schwartz
mesh_terms: D016118:Anterior Cruciate Ligament / Q000503:physiopathology; D001696:Biomechanical Phenomena; D005260:Female; D005684:Gait / Q000502:physiology*; D006801:Humans; D007718:Knee Injuries / Q000503:physiopathology; D007719:Knee Joint / Q000502:physiology* / Q000503:physiopathology; D008297:Male; D009068:Movement; D053580:Muscle Strength / Q000502:physiology*; D010003:Osteoarthritis / Q000503:physiopathology; D052097:Quadriceps Muscle / Q000502:physiology*; D012044:Regression Analysis
keywords: Anterior cruciate ligament; Arthrogenic muscle inhibition; Central activation ratio; Osteoarthritis