Nocturnal autonomic activity in athletes with regular versus prolonged return to sport after sport-related concussion

Sport-related concussion (SRC) is a multifaceted brain injury linked to altered autonomic activity, which may persist and contribute to prolonged recovery and persisting post-concussion symptoms (PPCS). This exploratory cross-sectional study addressed whether athletes with prolonged recovery show altered nocturnal autonomic activity after SRC, offering potential insights into PPCS and biomarkers. Nocturnal autonomic activity and concussion symptoms were evaluated and compared between 17 SRC athletes and 17 matched control athletes. SRC athletes were classified by individual return to sport (RTS) into regular RTS (< 28 days, n = 10) and prolonged RTS (≥ 28 days, n = 7). Nocturnalautonomic measures were collected during and post RTS (> 3 weeks) using a multimodal wearable device. Outcomes included heart rate (HR), HR variability (RMSSD), and electrodermal activity (EDA). No group differences in concussion symptoms, HR, RMSSD, and EDA were found during RTS. Post RTS, prolonged RTS athletes displayed significantly lower nocturnal RMSSD (p = 0.035, r = 0.612)than regular RTS athletes and controls. Additionally, prolonged RTS athletes exhibited fewer phasic EDA (sleep storms) compared to regular RTS athletes. Prolonged SRC recovery might be associated with reduced nocturnal parasympathetic (RMSSD) and phasic sympathetic (EDA) activity, after clinical symptom resolution. Further research is needed to explore whether this reflects insufficient physiological recovery or deconditioning. Keywords Concussion, sport, autonomic nervous system, sleep, heart rate variability, electrodermal activity