%I Academy of Science of South Africa %J South African Journal of Science %K UTCI, Comrades Marathon, heat stress, thermoregulation %L discovery10187914 %X An article in the July/August 2022 issue (Havenga et al., S Afr J Sci. 2022;118(7/8), Art. #13118) argued that changing the date of the Comrades Marathon from May to August would result in increased heat stress for participants. Heat stress was estimated using the Universal Thermal Climate Index (UTCI), which is designed to represent a person walking, not running. In this Commentary, I argue that using the UTCI may lead to an underestimation of heat stress for the Comrades Marathon, and that the conclusion that August has worse heat stress than May depends on the assumptions in the estimation of heat stress. %O This article is published under a Creative Commons Attribution 4.0 International Licence (http://creativecommons.org/licenses/by/4.0/). %T Comment on Havenga et al. (2022): Standard heat stress indices may not be appropriate for assessing marathons %V 120 %A CH Simpson %N 1/2 %D 2024