Weaker Quadriceps Corticomuscular Coherence in Individuals after ACL Reconstruction during Force Tracing

Abstract

PurposeThis study aimed to compare quadriceps corticomuscular coherence (CMC) and force steadiness between individuals with anterior cruciate ligament reconstruction (ACLR) and uninjured controls during a force tracing task.MethodsIndividuals with ACLR (n = 20) and controls (n = 20) performed a knee extension force-control task at 50% of maximal voluntary effort. Electrocortical activity, electromyographic activity, and torque output were recorded concurrently. CMC in beta (13–30 Hz) and gamma (31–80 Hz) frequency bands was assessed using partial directed coherence between the contralateral motor cortex (e.g., C4–C2–Cz electrodes) and the ipsilateral quadriceps muscles (e.g., left vastus medialis and lateralis). Force steadiness was quantified using root-mean-square error and coefficient of variation. Active motor threshold was determined using transcranial magnetic stimulation. Differences between groups (ACLR vs control) and limbs (involved vs uninvolved) were assessed using peak knee extension strength and active motor threshold as a priori covariates.ResultsParticipants with ACLR had lower gamma band connectivity bilaterally when compared with controls (vastus medialis: d = 0.8; vastus lateralis: d = 0.7). Further, the ACLR group demonstrated worse quadriceps force steadiness (root-mean-square error, d = 0.5), lower involved limb quadriceps strength (d = 1.1), and higher active motor threshold (d = 1.0) compared with controls.ConclusionsLower quadriceps gamma band CMC in the ACLR group suggests lower cortical drive (e.g., corticomotor decoupling) to the quadriceps compared with matched controls. Further, the ACLR group demonstrated worse quadriceps force steadiness, suggesting impaired ability to modulate quadriceps neuromuscular control. Notably, CMC differences were present only in the gamma frequency band, suggesting impairments may be specific to multisensory integration and force modulation.

Neural drive and motor unit characteristics after anterior cruciate ligament reconstruction: implications for quadriceps weakness

“…Key features of our sample, including full voluntary quadriceps activation and normal spinal reflexive excitability, support our interpretation of impairments in both motor neuron and morphological properties of muscle fibers. Accordingly, we discuss these results in the context of previously theorized reductions in cortical neural drive to the quadriceps ( Nuccio et al, 2021 ; Sherman et al, 2023 ), muscle fiber type transitions ( Lepley et al, 2020 ; Noehren et al, 2016 ) and reductions in quadriceps functional capacity due to catabolism of high threshold MUs following ACL injury or surgery ( Hunt et al, 2022 ).…”

“…Our sample was 2.4 years from surgery on average, a time point when spinal inhibition caused by arthrogenous pain and effusion is largely resolved ( Lepley et al, 2015 ; Rush, Glaviano & Norte, 2021 ). Conversely, reduced corticospinal excitability and cortical drive develop during periods of rehabilitation ( Rush, Glaviano & Norte, 2021 ; Sherman et al, 2023 ), persist into the long term, and contribute to persistent structural atrophy and reduced muscle capacity ( Birchmeier et al, 2020 ; Lisee et al, 2019 ).…”

“…Any person with known history of concussion in the past 6 months, neurological disorder, or who were taking medications which may alter neural excitability ( e.g ., stimulants and depressants) were excluded. Participants were instructed to avoid caffeine and alcohol for 24 h prior to testing ( Sherman et al, 2023 ). The University of Toledo Institutional Review Board for Biomedical Research approved this study (IRB # 300052-UT).…”

“…Participants were secured using chest and lap straps to reduce aberrant motion during testing. They completed a standardized, progressive, familiarization protocol consisting of progressive increases in perceived effort (25%, 50%, 75% effort) ( Sherman et al, 2023 ). During three MVIC trials, we instructed participants to kick out as hard and as fast as possible for five seconds as a TV monitor provided synchronized visual feedback of performance and 110% goal setting.…”

“…The maximal contractions followed a similar trapezoid pattern but with a 20% MVIC/s linear increase, a 5 s plateaued region, and a 20% MVIC/s linear decrease of torque. Participants used real-time torque feedback overlaid with a visual template of the isometric trapezoidal shape ( Sherman et al, 2023 ). Participants performed three repetitions at each intensity prior to continuing to the next in randomized order.…”