(English) Episode 57-Beyond Brute Strength - Unpacking ACL Recovery's Hidden Neural Control Deficits

Joint trauma induces a presynaptic reflex inhibition termed arthrogenic muscle inhibition (AMI) that prevents complete activation of muscles. Reduced motor unit (MU) output is a hypothesized mechanism for persistent strength deficits. The objective of this study was to determine MU characteristics of thigh musculature and determine how they change with anterior cruciate ligament (ACL) injury compared to healthy controls. A randomized protocol of knee flexion/extension isometric contractions (10–50% maximal voluntary isometric contraction) was performed for each leg with surface EMG 5-pin array electrodes placed on the vastus medialis, vastus lateralis, semitendinosus, and biceps femoris. Longitudinal assessments for average rate coding, recruitment thresholds, and MU action potentials were acquired at 6-month intervals.With exception of the vastus medialis, all thigh musculature of ACL-injured demonstrated smaller MU action potential peak-to-peak amplitude. For average rate coding, ACL-injured demonstrated lower coding rates than Controls for the quadriceps and higher rates than Controls for the hamstrings. These MU characteristics were different from Controls after ACL reconstruction up to 12 months post-surgery, yet maximal strength increased during this time frame. As thigh MU characteristics are known across phases of ACL rehabilitation, future studies can assess these patterns of motor control and its potential to determine risk of re-injury. Further, future rehabilitation can target specific intervention programs to restore motor control.(Schilaty ND, McPherson AL, Nagai T, Bates NA. Arthrogenic muscle inhibition manifests in thigh musculature motor unit characteristics after anterior cruciate ligament injury. EJSS (Champaign) [Internet]. 2023;23(5):840–50. Available from: http://dx.doi.org/10.1080/17461391.2022.2056520)