Effects of head impact exposure on in-game heart rate dynamics in Canadian varsity football athletes

ObjectivesTo characterize the association between head impact exposure (HIE) and heart rate (HR) dynamics during varsity football games. DesignProspective observational study following a convenience sample of 72 athletes over two seasons. MethodsAthletes wore instrumented mouthguards and chest-strap sensors to record HIE, HR, and velocity.After filtering for physiologically relevant recovery segments ( = 7,693), linear mixed-effects models assessed associations between HIE and HR dynamics, controlling for physical exertion and inter-individual variability.Exploratory non-linear associations were modeled using generalized additive mixed models (GAMMs). ResultsGreater acute impact magnitude was associated with elevated HR and delayed time to peak HR recovery ( < 0.001), independent of running speed.Random slopes analysis further indicated substantial inter-individual variability in the immediate cardiac response to impacts.Higher accumulated session-wide impact exposure demonstrated a non-linear relationship with HR recovery speed; recovery dynamics remained preserved at lower exposure levels (i.e., 200) but were progressively attenuated at higher cumulative loads (i.e., > 200).Conclusions HIE is associated with systematic alterations in HR recovery dynamics during live sport participation.These findings identify cardiovascular recovery as a sensitive, non-invasive physiological signal linked to head impacts, independent of measured locomotor workload variables.While clinical outcomes were not assessed, the results demonstrate the feasibility of integrated wearable monitoring to characterize physiological strain and J o u r n a l P r e -p r o o f Journal Pre-proof motivate future studies linking impact history with functional and clinical endpoints.