title: Impaired voluntary quadriceps force control following anterior cruciate ligament reconstruction: relationship with knee function.
abstract: OBJECTIVE
  Impairments in quadriceps force control and altered quadriceps and hamstring muscle activation strategies have been observed following anterior cruciate ligament reconstruction; however, the functional implications of these impairments are unclear. This study examined the cross-sectional associations between quadriceps force control, quadriceps activation, hamstring coactivation and clinically assessed knee function following anterior cruciate ligament reconstruction with a hamstring graft.
  
  
  METHODS
  Sixty-six patients (18 ± 3 months following surgery) and 41 uninjured individuals participated. Quadriceps force control was assessed using an isometric knee extension task. Participants cyclically increased and decreased quadriceps force at slow speeds between 5 and 30 % maximum voluntary isometric contraction matching a moving target displayed on a screen. Quadriceps activation and hamstring coactivation were assessed concurrently using surface electromyography. Knee function was assessed with the Cincinnati Knee Rating Scale and three single-leg hop tests.
  
  
  RESULTS
  The reconstructed group completed the task with 48 % greater root-mean-square error (RMSE), indicating significantly worse quadriceps force control (p < 0.001). In a multivariable model adjusted for sex, greater RMSE and greater lateral hamstring coactivation were significantly associated with worse knee function that is greater odds of scoring <85 % on one or more knee functional assessment.
  
  
  CONCLUSIONS
  Less-accurate quadriceps force output and greater hamstring coactivation are associated with worse knee joint function following anterior cruciate ligament reconstruction and may contribute to irregular knee joint loading and the onset or progression of knee osteoarthritis. Impairments in quadriceps force control and altered muscle activation strategies may be modifiable through neuromuscular training, and this is an area for future research.
  
  
  METHODS
  Case-control study, Level III.
authors.affiliation: Centre for Health, Exercise and Sports Medicine, Melbourne School of Physiotherapy, Faculty of Medicine Dentistry and Health Sciences, The University of Melbourne, Melbourne, VIC, 3010, Australia. lukeperraton@gmail.com.|School of Exercise Science, Faculty of Health Sciences, Australian Catholic University, Melbourne, VIC, Australia. lukeperraton@gmail.com.
authors.forename: Luke
authors.initials: L
authors.lastname: Perraton
authors.affiliation: School of Exercise Science, Faculty of Health Sciences, Australian Catholic University, Melbourne, VIC, Australia.
authors.forename: Ross
authors.initials: R
authors.lastname: Clark
authors.affiliation: School of Allied Health, La Trobe University, Bundoora, VIC, Australia.
authors.forename: Kay
authors.initials: K
authors.lastname: Crossley
authors.affiliation: Department of Physiotherapy, Singapore General Hospital, Singapore, Singapore.
authors.forename: Yong-Hao
authors.initials: YH
authors.lastname: Pua
authors.affiliation: Orthosport Victoria, Epworth Hospital, Melbourne, VIC, Australia.
authors.forename: Tim
authors.initials: T
authors.lastname: Whitehead
authors.affiliation: The Park Clinic, Melbourne, VIC, Australia.
authors.forename: Hayden
authors.initials: H
authors.lastname: Morris
authors.affiliation: Centre for Health, Exercise and Sports Medicine, Melbourne School of Physiotherapy, Faculty of Medicine Dentistry and Health Sciences, The University of Melbourne, Melbourne, VIC, 3010, Australia.
authors.forename: Stacey
authors.initials: S
authors.lastname: Telianidis
authors.affiliation: Centre for Health, Exercise and Sports Medicine, Melbourne School of Physiotherapy, Faculty of Medicine Dentistry and Health Sciences, The University of Melbourne, Melbourne, VIC, 3010, Australia.
authors.forename: Adam
authors.initials: A
authors.lastname: Bryant
mesh_terms: D000328:Adult; D016118:Anterior Cruciate Ligament / Q000503:physiopathology* / Q000601:surgery; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods / Q000534:rehabilitation*; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D005260:Female; D000070633:Hamstring Muscles / Q000503:physiopathology* / Q000637:transplantation; D006801:Humans; D007717:Knee / Q000503:physiopathology* / Q000601:surgery; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D052097:Quadriceps Muscle / Q000503:physiopathology*; D020127:Recovery of Function; D055815:Young Adult
keywords: ACL reconstruction; Knee function; Muscle activation; Quadriceps force control