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To examine the relationship between cerebral autoregulation changes and impact exposuresthroughout a season of contact sports (hockey or football).Prospective Cohort.Laboratory.40 male contact sport athletes (19.4±1.2 years); to date, 3 cross-country athletes (20.0±1.0 years) have completed testing (non-contact controls).Participants completed testing prior to the start of their athletic seasons (T1), and again after the conclusion of each season (T2). Blood pressure (BP) oscillations were driven by stand-squat manoeuvres at 0.05 and 0.10 Hz. BP and cerebral blood velocity (CBV) in the middle cerebral artery were indexed non-invasively using finger photoplethysmography and transcranial Doppler ultrasound, respectively. RM-ANOVA independent variables included time (2) and frequency (2).Point-estimates of coherence (correlation), phase (synchronisation), and gain (amplitude buffer) transfer function analysis metrics were calculated. Biomechanical data on head-impact exposure was estimated in a subset of contact-sport athletes (n=29) using the xPatch (X2 Biosystems), affixed to the right mastoid.Significant frequency-time interaction for gain in contact-sport athletes (p=0.048) but not controls (p=0.213). Simple effects analysis revealed a time effect at 0.10 Hz (p<0.001), whereby gain increased at T2 (95% CI: 0.070–0.229%/%). The ΔgainT2-T1 at 0.10 Hz was correlated withestimated cumulativerotational acceleration exposure (r=0.462, p=0.015).These findings suggest cumulative exposure to the rotational component of sustained head-impactsduring participation in a season of contact-sport (hockey or football) impairs the ability of the cerebrovasculature to buffer BP challenges experienced during everyday activities.None.