Persistent Muscle Inhibition after Anterior Cruciate Ligament Reconstruction: Role of Reflex Excitability

Matthew S. Harkey, Brittney A. Luc-Harkey, Adam S. Lepley, Terry L. Grindstaff, Phillip Gribble, J. Troy Blackburn, Jeffrey T. Spang, Brian Pietrosimone

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Purpose 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. Methods 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). Results 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). Conclusions 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.

Original languageEnglish
Pages (from-to)2370-2377
Number of pages8
JournalMedicine and Science in Sports and Exercise
Issue number12
StatePublished - Dec 1 2016

Bibliographical note

Publisher Copyright:
© 2016 by the American College of Sports Medicine.



ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Physical Therapy, Sports Therapy and Rehabilitation


Dive into the research topics of 'Persistent Muscle Inhibition after Anterior Cruciate Ligament Reconstruction: Role of Reflex Excitability'. Together they form a unique fingerprint.

Cite this