title: Quadriceps Function and Hamstrings Co-Activation After Anterior Cruciate Ligament Reconstruction.
abstract: BACKGROUND
  Individuals with anterior cruciate ligament reconstruction (ACLR) have quadriceps dysfunction that contributes to physical disability and posttraumatic knee osteoarthritis. Quadriceps function in the ACLR limb is commonly evaluated relative to the contralateral uninjured limb. Bilateral quadriceps dysfunction is common in individuals with ACLR, potentially biasing these evaluations.
  
  
  OBJECTIVE
  To compare quadriceps function between individuals with ACLR and uninjured control participants.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  Research laboratory.
  
  
  METHODS
  Twenty individuals with unilateral ACLR (age = 21.1 ± 1.7 years, mass = 68.3 ± 14.9 kg, time since ACLR = 50.7 ± 21.3 months; females = 14; Tegner Score = 7.1 ± 0.3; 16 patellar tendon autografts, 3 hamstrings autografts, 1 allograft) matched to 20 control participants (age = 21.2 ± 1.2 years, mass = 67.9 ± 11.3 kg; females = 14; Tegner Score = 7.1 ± 0.4) on age, sex, body mass index, and Tegner Activity Scale.
  
  
  METHODS
  Maximal voluntary isometric knee extension was performed on an isokinetic dynamometer. Peak torque (PT), rate of torque development (RTD), electromyographic (EMG) amplitude, central activation ratio (CAR), and hamstrings EMG amplitude were assessed during maximal voluntary isometric knee extension and compared between groups using independent-samples t tests. Relationships between hamstrings co-activation and quadriceps function were assessed using Pearson correlations.
  
  
  RESULTS
  Participants with anterior cruciate ligament reconstruction displayed lesser quadriceps PT (1.86 ± 0.74 versus 2.56 ± 0.37 Nm/kg, P = .001), RTD (39.4 ± 18.7 versus 52.9 ± 16.4 Nm/s/kg, P = .03), EMG amplitude (0.25 ± 0.12 versus 0.37 ± 0.26 mV, P = .04), and CAR (83.3% ± 11.1% versus 93.7% ± 3.2%, P = .002) and greater hamstrings co-activation (27.2% ± 12.8% versus 14.3% ± 3.7%, P < .001) compared with control participants. Correlations were found between hamstrings co-activation and PT (r = -0.39, P = .007), RTD (r = -0.30, P = .03), and EMG amplitude (r = -0.30, P = .03).
  
  
  CONCLUSIONS
  Individuals with ACLR possessed deficits in PT, RTD, and CAR compared with control participants. Peak torque is the net result of all agonist and antagonist activity, and lesser PT in individuals with ACLR is partially attributable to greater hamstrings co-activation.
authors.affiliation: California State University, Fullerton.
authors.forename: Derek N
authors.initials: DN
authors.lastname: Pamukoff
authors.affiliation: University of North Carolina at Chapel Hill.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Pietrosimone
authors.affiliation: University of North Carolina at Chapel Hill.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Ryan
authors.affiliation: University of North Carolina at Chapel Hill.
authors.forename: Dustin R
authors.initials: DR
authors.lastname: Lee
authors.affiliation: University of North Carolina at Chapel Hill.
authors.forename: J Troy
authors.initials: JT
authors.lastname: Blackburn
mesh_terms: D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries / Q000150:complications / Q000601:surgery; D059549:Anterior Cruciate Ligament Reconstruction / Q000009:adverse effects / Q000534:rehabilitation; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D020370:Osteoarthritis, Knee / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D052097:Quadriceps Muscle / Q000503:physiopathology*; D016059:Range of Motion, Articular
keywords: arthrogenic muscle inhibition; electromyography; muscles; strength