Heat preparation and nutrition strategies for a 100-mile ultramarathon in extreme hot conditions: A questionnaire study at the Western States Endurance Run

Abstract Objectives This study examined heat preparation, nutritional strategies, and gastrointestinal (GI) symptoms of runners competing in the 2025 Western States Endurance Run (WSER), a 100-mile ultra-marathon with extreme heat exposure. Design 1. Cross-sectional, 2. Prospective observational study. Methods Pre- and post-race surveys (n = 106 pre-race; n = 66 post-race) collected data on demographics, heat experience, heat acclimat(isat)ion, nutrition and hydration strategies, and race-related symptoms. Finishers were grouped by race time (<18 h, 18–24 h, 24–30 h). Chi-square tests with Cramer's V evaluated associations between variables and performance categories. Results Most runners (90%) completed heat preparation, including acclimatisation (67%) and acclimation (70%), with >70% reporting >10 days or exposures. Mid-race cooling strategies were planned by 92%, mainly neck collars (89%) and cold towels (52%). Most (96%) runners tested their strategies during training. Faster finishers were more likely to have structured carbohydrate plans (<18 h: 100% vs 24–30 h: 69%; χ² = 8.43; P = 0.015) and higher sodium intake (χ² = 17.64; P = 0.007). GI symptoms occurred in 63% of finishers and 38% of those who dropped out. Symptoms were most frequent in slower runners (χ² = 17.2; P = 0.045). No differences in heat-related symptoms were observed between groups. Conclusions Runners were highly heat-prepared and widely adopted cooling strategies, likely facilitated by pre-race communication, logistics, and prior experience. This, in addition to tested nutritional strategies may have contributed to fewer severe GI issues compared with previous studies.