Author(s): UDDIN, N., SCHOENMAKERS, P., ADAMS, T., VOYEVODA, L., JONES, B., PATTERSON, S., KIDGELL, D., PEARCE, A., WALDRON, M., TALLENT, J., Institution: UNIVERSITY OF ESSEX, Country: UNITED KINGDOM, Abstract-ID: 193

INTRODUCTION:
Combat sports, such as boxing, consistently report some of the highest concussion rates per 100,000 athletic events. Despite this, limited research has examined the cumulative head impacts sustained during training, or the acute neurophysiological responses to a single sparring session. Using instrumented mouthguards (IMG), transcranial magnetic stimulation (TMS), and peripheral nerve stimulation (PNS), this naturalistic observational study examined acute changes in corticospinal and peripheral neuromuscular function following combat sport sparring.
METHODS:
13 male competitive amateur combat sports athletes (age: 23 ± 5yrs, stature: 175 ± 8cm, BM: 74 ± 17kg) completed TMS & PNS testing before, immediately, and 48h after a single sparring session. In addition, five athletes from this cohort (age: 25 ± 6yrs, stature: 180 ± 11cm, BM: 83 ± 26kg) wore IMGs and were monitored before and immediately after multiple sessions. Outcome measures included Active Motor Threshold (AMT), Maximal Voluntary Contraction (MVC), Compound Muscle Action Potential (MMAX), Motor Evoked Potential (MEP), and Cortical Silent Period (cSP).
RESULTS:
Participants took part in 15 ± 2 min of sparring (min: 8 min, max: 20 min) and sustained a median head impact frequency (HIF) of 19 (IQR: 36) in a single session. The highest peak linear acceleration (PLA) and peak angular acceleration (PAA) recorded were 50 g and 5775 rad/s², respectively. Mean PLA per impact was 12 ± 6 g, while mean PAA was 1048 ± 622 rad/s². Cumulative load (sum of all impact load) per session totalled 240 ± 136 g for PLA (CLA) and 20,421 ± 11,910 rad/s² for PAA (CAA). AMT increased post-sparring (p = .024 ) while MMAX decreased immediately post (p = .031; .018) but returned to baseline by 48 hours. MEP amplitude decreased post (p < .001) and remained suppressed at 48 hours (p = .034), while cSP duration increased post-sparring (p = .044) and did not return to baseline at 48 hours. Significant positive repeated measures correlations (p < .001) were observed between cSP duration and HIF (r = 0.69), CLA (r = 0.89), and CAA (r = 0.91). In addition, a linear mixed model demonstrated that HIF (β = 1.27), CLA (β = 0.91), and CAA (β = 1.08) were significant predictors (p < .001) of cSP change after accounting for participant-level variability.
CONCLUSION:
These findings provide novel evidence that a typical combat sport sparring session can result in suppressed MEP amplitude, prolonged cSP, and elevated motor threshold, suggesting transient neurophysiological disruption following repeated head impacts after a single session. Furthermore, head impact characteristics, particularly CAA, are strongly associated with the observed transient GABAB-mediated inhibitory upregulation post-impact. Mechanistically, these findings reinforce rotational acceleration as a primary driver of acute neurophysiological disturbance following head impacts, likely reflecting load-dependent modulation of cortical inhibitory circuitry in response to repeated head impacts.