title: Contributions of neural excitability and voluntary activation to quadriceps muscle strength following anterior cruciate ligament reconstruction.
abstract: BACKGROUND
  Persistent quadriceps weakness is common following anterior cruciate ligament reconstruction (ACLr). Alterations in spinal-reflexive excitability, corticospinal excitability and voluntary activation have been hypothesized as underlying mechanisms contributing to quadriceps weakness. The aim of this study was to evaluate the predictive capabilities of spinal-reflexive excitability, corticospinal excitability and voluntary activation on quadriceps strength in healthy and ACLr participants.
  
  
  METHODS
  Quadriceps strength was measured using maximal voluntary isometric contractions (MVIC). Voluntary activation was quantified via the central activation ratio (CAR). Corticospinal and spinal-reflexive excitability were measured using active motor thresholds (AMT) and Hoffmann reflexes normalized to maximal muscle responses (H:M), respectively. ACLr individuals were also split into high and low strength subsets based on MVIC.
  
  
  RESULTS
  CAR was the only significant predictor in the healthy group. In the ACLr group, CAR and H:M significantly predicted 47% of the variance in MVIC. ACLr individuals in the high strength subset demonstrated significantly higher CAR and H:M than those in the low strength subset.
  
  
  CONCLUSIONS
  Increased quadriceps voluntary activation, spinal-reflexive excitability and corticospinal excitability relates to increased quadriceps strength in participants following ACLr.
  
  
  CONCLUSIONS
  Rehabilitation strategies used to target neural alterations may be beneficial for the restoration of muscle strength following ACLr.
authors.affiliation: Musculoskeletal Health and Movement Science Laboratory, Department of Kinesiology, University of Toledo, Toledo, OH, United States. Electronic address: adam.lepley@rockets.utoledo.edu.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Lepley
authors.affiliation: Musculoskeletal Health and Movement Science Laboratory, Department of Kinesiology, University of Toledo, Toledo, OH, United States.
authors.forename: Hayley M
authors.initials: HM
authors.lastname: Ericksen
authors.affiliation: Department of Orthopedic Surgery, University of Toledo, Toledo, OH, United States.
authors.forename: David H
authors.initials: DH
authors.lastname: Sohn
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Pietrosimone
mesh_terms: D059549:Anterior Cruciate Ligament Reconstruction; D016022:Case-Control Studies; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D053581:Muscle Strength Dynamometer; D052097:Quadriceps Muscle / Q000502:physiology*; D012021:Reflex, Abnormal / Q000502:physiology; D012044:Regression Analysis; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: Corticospinal excitability; Knee injury; Neuromuscular function; Quadriceps weakness; Spinal-reflexive excitability