Exercise intolerance and time to medical clearance to return to sport following sport-related concussion in adolescents.

Objective: Recovery duration following adolescent sport-related concussion (SRC) is variable. Previous research revealed exercise intolerance is associated with delayed recovery (predominantly male Australian cohort). Additional sport contexts and considerations of sex are necessary. This study investigated sex-specific associations between exercise intolerance and time-to-medical clearance to return-to-sport (RTS) following SRC in adolescents (ages 10-19). Methods: Adolescent athletes participating in the pan-Canadian SHRed Concussions cohort study were included within 14 days following a physician diagnosed SRC. Participants completed the Buffalo Concussion Treadmill Test (BCTT). Pre-BCTT Sport Concussion Assessment Tool 5 (SCAT5) Symptom Severity Score (SSS;/132) and concussion Overall Condition score (OC;/10) were recorded. Termination criteria for BCTT were participants who experienced ≥3/10 increase for OC (exercise intolerant) or reached volitional fatigue (≥180bpm, ≥18/20 rating of perceived exertion, exercise tolerant). Results: 281 adolescents (126 male and 155 female), of whom 204 (72.6%) (100 male (79.4%), 104 female (67.1%)) were exercise tolerant and 77 (27.4%) (26 male (20.6%), 51 female (32.9%)) were intolerant following SRC. Based on the point estimate, females had a 1.45 times higher risk of exercise intolerance compared with males (risk ratio=1.45, 95% CI 0.96 to 2.20). Exercise intolerance was associated with a 36% longer medical clearance time to RTS following SRC for females (time ratio=1.36, 95% CI 1.12 to 1.64), while for males, no association was observed (time ratio=1.13, 95% CI 0.90 to 1.42) (adjusted for age, BCTT duration, SCAT5 SSS and days from SRC to BCTT). Conclusion: Exertion testing may identify female adolescents at higher risk of delayed medical clearance recovery to RTS, informing the comprehensive clinical management of SRC.