Altered Motor Unit Characteristics of Cervical Neuromuscular Function Following Sports-Related Concussion: A Pilot Study

Objectives: To examine the impact of sports-related concussion (SRC) on cervical neuromuscular function by evaluating motor unit (MU) behavior of the sternocleidomastoid (SCM) and upper trapezius (UT) muscles using decomposed electromyography (dEMG). Design: Matched case-control study. Setting: Laboratory-based experimental study conducted using a custom-built isometric neck strength device. Participants: Twenty-six adolescent athletes (12–20 years) participating in competitive sports, including 13 with a history of clinically diagnosed SRC (CONC) and 13 matched healthy controls (CTRL). Main Outcome Measures: From dEMG, MU action potential (MUAP) amplitude, average firing rate (AvgFR), and total motor unit contribution of the SCM and UT during isometric neck contractions (flexion, extension, and bilateral lateral flexion) were extracted. Results: No significant between-group differences were observed for average firing rate (AvgFR) or total motor unit contribution in either the SCM or UT. For MUAP, differences were identified in the UT during left lateral bending (p = 0.024) and right lateral bending (p = 0.045), accompanied by medium-to-large effect sizes across all contraction directions. Linear regression analyses demonstrated strong recruitment-related associations for AvgFR, MUAP, and total motor unit contribution in both groups, although lower R2 values were generally observed in the CONC group compared to CTRL. Conclusions: SRC is associated with persistent alterations in cervical neuromuscular function, particularly within the UT. Task-specific differences in MUAP observed during lateral bending tasks suggest that neuromuscular adaptations may persist beyond clinical recovery and occur in a muscle- and direction-specific manner. These findings indicate persistent neuromuscular deficits in the neck musculature following SRC and highlight the importance of targeted rehabilitation to restore motor control and reduce reinjury risk.