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Introduction. Big wave surfing (waves ≥15 feet) represents one of the least-studied high-risk sport populations in concussion research. Athletes experience repeated high-energy inertial loading, extended breath-hold intervals, and hydrodynamic forces analogous to acceleration-deceleration mechanisms responsible for mild traumatic brain injury (mTBI) in contact and combat sports. No prospective study has monitored neurological and biometric outcomes longitudinally in this population. This study aimed to characterize concussion threshold-crossing events in experienced big wave surfers, examine associations between ocean exposure variables and neurological outcomes, and evaluate the feasibility of continuous biometric monitoring as a complement to standardized clinical assessment.

Methods. Twenty-two participants were enrolled in a prospective observational longitudinal study (July 2025–March 2026). Inclusion required age ≥13 years, and professional or experienced big wave surfing intent. Baseline and post-session assessments included the SCAT-6 and SCOAT-6, administered via REDCap. Participants wore Oura Ring sensors continuously throughout the study. Swell conditions were self-reported as informed by Surfline. Raw data were processed through a seven-stage Python pipeline, producing a final analytic dataset of 203 surf sessions across 20 participants. Six binary concussion flags were applied based on published clinical thresholds. Statistical analyses included Spearman rank correlation, within-participant centering regression, and linear and generalized linear mixed-effects models with random intercepts per participant.

Results. Across 203 surf sessions (20 participants; mean 10.2 sessions/participant, range 1–71), concussion flag rates per session were: Symptom Severity Score 16.7% (≥4-point increase), Symptom Count 21.7% (≥2 new symptoms), Anxiety Score 15.3%, Depression Score 8.9%, Modified Sleep Score 31.5%, and SAC Score Decline 30.5% (≥2-point decline). At least one flag was triggered in 65.0% of sessions; 35% triggered two or more flags simultaneously. Among the 16 participants with ≥3 sessions, the mean within-participant any-flag rate was 73.6%, and both Modified Sleep Score and SAC Decline flags were triggered by every participant at least once. Subjective head impact severity was the single strongest predictor of post-surf symptom burden across all analytic approaches, surviving Bonferroni correction: each 1-SD increase was associated with a 3.27-point increase in Symptom Score (β = +3.273, t(15) = 4.68, p = 0.0003) and 1.91 additional symptoms endorsed (t(15) = 5.92, p < 0.0001). Total hits and inertial non-impact loads independently predicted next-day Oura Readiness Score decline (β ≈ −2.1 per SD, both p < 0.01). Swell energy independently predicted symptom burden within participants (both p < 0.05). SAC-flagged sessions were associated with lower next-day Oura Activity Score (d = −0.700, p = 0.021); Symptom Count-flagged sessions predicted lower sleep efficiency and longer sleep latency (both p < 0.05). Temperature deviation showed a non-significant medium effect on SAC-flagged nights (d ≈ 0.35).

Discussion. These findings demonstrate that neurological and biometric responses to big wave surfing are detectable, quantifiable, and systematically associated with measurable exposure variables. The dominance of subjective impact severity over objective hit count suggests that athlete perception integrates biomechanically relevant information beyond discrete event tallies. The equivalence of inertial non-impact loads and total hits in predicting biometric recovery suppression implicates hydrodynamic forces — rather than direct solid-object contact — as a primary physiological cost driver. The near-universal occurrence of sleep and cognitive flags raises the interpretive question of whether these reflect expected physiological consequences of extreme exertion rather than discrete concussive events — a confound that the current design cannot resolve without matched non-impact exertion controls. Limitations include pilot sample size (n = 20), reliance on self-report, incomplete swell data coverage, and absence of concurrent head impact instrumentation.

Conclusion. This pilot study provides the first prospective, multi-session, multi-modal characterization of neurological and biometric responses to big wave surfing across a competitive season. Experienced big wave surfers regularly cross clinical concussion thresholds; subjective impact severity and swell energy independently predict symptom burden; and continuous wearable monitoring detects post-session physiological disruption consistent with neurological stress. These findings establish an empirical foundation for this understudied domain and motivate larger instrumented studies with objective biomechanical measurement and exertion control conditions.