title: Time course of quad strength, area, and activation after knee arthroplasty and strength training.
abstract: BACKGROUND
  changes in strength, activation, and morphology of the quadriceps femoris muscle group were assessed in 61 individuals that underwent unilateral total knee arthroplasty, with progressive postoperative strength training, for primary knee osteoarthritis.
  
  
  METHODS
  assessments of these three parameters were made at four time points (preoperatively and 4, 12, and 52 wk postoperatively). Maximal voluntary knee extension strength was recorded using an electromechanical dynamometer, and voluntary muscle activation was measured using a burst superimposition technique. Lean muscle cross-sectional area (CSA) was determined using magnetic resonance imaging.
  
  
  RESULTS
  preoperatively, the surgical limb was significantly weaker and smaller than the nonsurgical limb. Strength, voluntary muscle activation, and CSA of the quadriceps femoris significantly improved over the study period. At 52 wk, the surgical limb was still significantly smaller than the nonsurgical limb but had greater levels of voluntary muscle activation. In the nonsurgical limb, CSA was the primary determinant of strength across all time points, with voluntary muscle activation progressively contributing more from the preoperative assessment (R = 0.11) to the assessment 52 wk postoperatively (R = 0.26). In the surgical limb, voluntary muscle activation was the primary determinant of strength preoperatively and 4 wk postoperatively (R = 0.38 and 0.41, respectively), whereas CSA was the primary determinant of quadriceps strength 12 and 52 wk postoperatively (R = 0.44).
  
  
  CONCLUSIONS
  resolving the impairments in voluntary muscle activation after total knee arthroplasty may be necessary before visible gains in strength and muscle hypertrophy are evident.
authors.affiliation: Department of Physical Therapy, University of Delaware, Newark, DE, USA.
authors.forename: Stephanie C
authors.initials: SC
authors.lastname: Petterson
authors.forename: Peter
authors.initials: P
authors.lastname: Barrance
authors.forename: Adam R
authors.initials: AR
authors.lastname: Marmon
authors.forename: Thomas
authors.initials: T
authors.lastname: Handling
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Buchanan
authors.forename: Lynn
authors.initials: L
authors.lastname: Snyder-Mackler
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000534:rehabilitation*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology*; D018908:Muscle Weakness / Q000503:physiopathology* / Q000534:rehabilitation; D019637:Orthopedic Procedures / Q000534:rehabilitation; D020370:Osteoarthritis, Knee / Q000534:rehabilitation / Q000601:surgery; D011184:Postoperative Period; D052097:Quadriceps Muscle / Q000502:physiology*; D055070:Resistance Training