Mitigating exertional heat illness risk and preserving performance in mass-participation endurance events: a real-world analysis of a graded cooling and fluid replacement strategy.

OBJECTIVES: Endurance athletes competing in hot-humid environments face substantial thermoregulatory strain. This study evaluated whether participation in a structured graded cooling and fluid replacement program was associated with lower post-race core body temperature and improved physiological, medical, and performance outcomes. DESIGN: Retrospective comparative analysis of a prospectively collected, non-randomized event-based cohort. METHODS: Records from 312 endurance athletes competing in four hot-humid events in southern China (2023-2025) were analyzed. Propensity score matching within event retained 116 matched pairs. The primary outcome was post-race core body temperature; secondary outcomes included race-time deviation, heat-related medical encounters, cortisol, and interleukin-6. RESULTS: Post-race core body temperature was lower with graded cooling and fluid replacement (39.1 ± 0.4°C vs 39.6 ± 0.5°C; mean difference -0.50°C, 95% confidence interval -0.62 to -0.38; P < 0.001). Race-time deviation from personal best was smaller (+4.8 ± 2.9% vs +8.3 ± 4.1%); adjusted between-group difference was -3.08 percentage points (95% confidence interval -4.21 to -1.95; P < 0.001). Heat-related medical encounters occurred in 10/116 versus 20/116 athletes (conditional OR 0.41, 95% confidence interval 0.17-0.99). Cortisol and interleukin-6 responses were attenuated. CONCLUSIONS: Participation in the structured program was associated with lower thermal strain, fewer heat-related medical presentations, and better preservation of race performance. The findings support the feasibility of organizer-delivered multimodal cooling and individualized fluid replacement in hot-humid endurance events.