title: Persistent Muscle Inhibition after Anterior Cruciate Ligament Reconstruction: Role of Reflex Excitability.
abstract: Persistent voluntary quadriceps activation deficits are common after anterior cruciate ligament reconstruction (ACLR), but the direct causes are unclear. The primary purpose of this study was to determine whether spinal reflex excitability deficits are present in individuals with a history of ACLR, and secondarily to determine whether spinal reflex excitability predicts which individuals possess full voluntary quadriceps activation.
  
  
  
  One hundred and forty-seven individuals (74 healthy and 73 ACLR) participated in this cross-sectional case-control study. Quadriceps spinal reflex excitability was quantified using the Hoffmann reflex normalized to the maximal muscle response (H:M ratio). Voluntary quadriceps activation was evaluated with the burst superimposition technique and calculated via the central activation ratio (CAR). Separate 2 × 2 ANCOVA tests were used to compare between-limb and between-group differences for H:M ratio and CAR. A receiver operating characteristic curve was used to determine the accuracy of H:M ratio to predict if ACLR participants present with full voluntary activation (CAR ≥ 0.95).
  
  
  
  The ACLR H:M ratio was not different between limbs or compared with the healthy group (P > 0.05). Although ACLR CAR was lower bilaterally compared with the healthy group (P < 0.001), it did not differ between limbs. The H:M ratio has poor accuracy for predicting which individuals exhibit full voluntary activation (receiver operating characteristic area under the curve = 0.52, 95% CI = 0.37,0.66; odds ratio = 2.2, 95% CI = 0.8, 5.9).
  
  
  
  Spinal reflex excitability did not differ between limbs in individuals with ACLR or compared with healthy participants. The level of quadriceps spinal reflex excitability has poor accuracy at predicting which ACLR individuals would demonstrate full voluntary quadriceps activation.
authors.affiliation: 1Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, NC; 2Human Movement Science Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, NC; 3Department of Kinesiology, University of Connecticut, Storrs, CT; 4Physical Therapy Department, Creighton University, Omaha, NE; 5Department of Rehabilitation Sciences, University of Kentucky, Lexington, KY; and 6Department of Orthopaedics, School of Medicine, University of North Carolina at Chapel Hill, NC.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Harkey
authors.forename: Brittney A
authors.initials: BA
authors.lastname: Luc-Harkey
authors.forename: Adam S
authors.initials: AS
authors.lastname: Lepley
authors.forename: Terry L
authors.initials: TL
authors.lastname: Grindstaff
authors.forename: Phillip
authors.initials: P
authors.lastname: Gribble
authors.forename: J Troy
authors.initials: JT
authors.lastname: Blackburn
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Spang
authors.forename: Brian
authors.initials: B
authors.lastname: Pietrosimone
mesh_terms: D000070598:Anterior Cruciate Ligament Injuries / Q000503:physiopathology / Q000601:surgery*; D059549:Anterior Cruciate Ligament Reconstruction; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D052097:Quadriceps Muscle / Q000503:physiopathology*; D020127:Recovery of Function / Q000502:physiology; D012021:Reflex, Abnormal / Q000502:physiology*; D013127:Spinal Nerves / Q000502:physiology* / Q000503:physiopathology; D055815:Young Adult