What do thermal indices lack to help predict heat-related risk in elite Athletics?

Objectives:
This study aimed to characterise the frequency of exertional heat stroke (EHS), did-not-finish (DNF) and medical encounter (MED) outcomes in elite Athletics competitions, and to evaluate their association with environmental, individual and race-related variables. Particular attention was given to the wet bulb globe temperature (WBGT), a thermal index widely used by international federations to estimate athlete heat strain.

Methods:
Data were collected from 4938 athletes of both sexes participating in 80 World Athletics races held between 2019 and 2024 in five disciplines: long distance track events, marathon, racewalking, cross-country and trail-running. Spearman rank coefficient correlations, Pearson χ2 tests and negative binomial (NB) regressions were used to explore associations between outcomes (EHS, DNF, MED) and environmental, individual and race-related variables. The predictive ability of these variables was assessed using leave-one-out cross-validation to identify the best-performing univariable and multivariable models.

Results:
EHS frequency was 8/1000 on average and 16/1000 when the WBGT was above 28.0°C, independent of sex (p=0.297) or discipline (p=0.980). DNF and MED were higher in marathon, racewalking and trail-running than shorter disciplines (p<0.001). Among variables, the mean radiant temperature showed the strongest univariable association with EHS (R²=0.11, p<0.001), while WBGT association was weaker (R²=0.04, p=0.018). Predictive accuracy was limited, with the best model having an error of 0.5±0.7 EHS per race.

Conclusion:
The risk of EHS is particularly high during elite endurance events in Athletics. While EHS was greater with higher WBGT and radiant temperatures, neither provided sufficient predictive accuracy for heat-related risk in elite endurance athletes. Future models should consider other factors such as heat acclimatisation and recent illness to enhance predictive ability.