title: Pre-operative quadriceps activation is related to post-operative activation, not strength, in patients post-ACL reconstruction.
abstract: OBJECTIVE
  Quadriceps activation failure is considered to contribute to the weakness that lingers following anterior cruciate ligament (ACL) reconstruction. Importantly, the impact of pre-operative quadriceps activation on post-operative quadriceps function is unknown. Understanding this relationship is clinically important; as the counteractive approach clinicians should employ pre-operatively to mitigate post-operative quadriceps weakness is unclear. Accordingly, the primary purpose of this study was to investigate the relationship between pre-operative quadriceps activation and post-operative quadriceps strength and activation.
  
  
  METHODS
  Fifty-four individuals post-ACL injury reported for testing on two occasions: prior to surgery and post-surgery once they returned to activity. Quadriceps activation was assessed using the burst superimposition technique and quantified using the central activation ratio. Quadriceps strength was assessed using isometric contractions that were performed at 90° of knee flexion. Multiple linear regressions were utilized to detect the relationships between pre-operative activation and strength and post-operative activation and strength.
  
  
  RESULTS
  Pre-operative activation was not associated with post-operative strength (R(2) = 0.064, P = 0.186). Pre-operative quadriceps activation and strength were associated with post-operative activation (R(2) = 0.383, P ≤ 0.001) and strength (R(2) = 0.465, P ≤ 0.001), respectively.
  
  
  CONCLUSIONS
  Individuals with better pre-operative quadriceps activation demonstrated greater post-operative activation. Similarly, individuals with better pre-operative strength demonstrated better post-operative strength. Pre-operative quadriceps activation was not a predictor of post-operative strength. From a clinical perspective, our work indicates that clinicians should utilize therapies targeting both quadriceps activation and strength prior to ACL reconstruction in order to maximize these factors post-ACL reconstruction, as pre-operative activation and strength are related to post-operative activation and strength, respectively at return-to-activity.
authors.affiliation: Department of Rehabilitation Sciences, University of Kentucky, Lexington, KY, USA. lindsey.lepley@uky.edu.|School of Kinesiology, University of Michigan, 4745G Central Campus Recreational Building, 401 Washtenaw Ave., Ann Arbor, MI, 48109, USA. lindsey.lepley@uky.edu.
authors.forename: Lindsey K
authors.initials: LK
authors.lastname: Lepley
authors.affiliation: School of Kinesiology, University of Michigan, 4745G Central Campus Recreational Building, 401 Washtenaw Ave., Ann Arbor, MI, 48109, USA. riannp@umich.edu.|Department of Orthopedic Surgery, University of Michigan, Ann Arbor, MI, USA. riannp@umich.edu.
authors.forename: Riann M
authors.initials: RM
authors.lastname: Palmieri-Smith
mesh_terms: D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction / Q000534:rehabilitation; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D007718:Knee Injuries / Q000601:surgery; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength; D011184:Postoperative Period; D057234:Preoperative Period; D052097:Quadriceps Muscle / Q000503:physiopathology*; D055815:Young Adult
keywords: ACL; Arthrogenic inhibition; Central activation ratio; Muscle; Muscle inhibition