Heat Acclimatization, Cooling Strategies, and Hydration during an Ultra-Trail in Warm and Humid Conditions

Nutrients. 2021 Mar 26;13(4):1085. doi: 10.3390/nu13041085.


The aim of this study was to assess the history of exertional heat illness (EHI), heat preparation, cooling strategies, heat related symptoms, and hydration during an ultra-endurance running event in a warm and humid environment. This survey-based study was open to all people who participated in one of the three ultra-endurance races of the Grand Raid de la Réunion. Ambient temperature and relative humidity were 18.6 ± 5.7 °C (max = 29.7 °C) and 74 ± 17%, respectively. A total of 3317 runners (56% of the total eligible population) participated in the study. Overall, 78% of the runners declared a history of heat-related symptoms while training or competing, and 1.9% reported a previous diagnosis of EHI. Only 24.3% of study participants living in temperate climates declared having trained in the heat before the races, and 45.1% of all respondents reported a cooling strategy during the races. Three quarter of all participants declared a hydration strategy. The planned hydration volume was 663 ± 240 mL/h. Fifty-nine percent of the runners had enriched their food or drink with sodium during the race. The present study shows that ultra-endurance runners have a wide variability of hydration and heat preparation strategies. Understandings of heat stress repercussions in ultra-endurance running need to be improved by specific field research.

Keywords: acclimatization; body temperature regulation; dehydration; electrolyte balance; hot temperature; hydration; running; ultra-endurance running.

MeSH terms

  • Acclimatization / physiology*
  • Adult
  • Drinking
  • Female
  • Heat Stress Disorders / prevention & control*
  • Hot Temperature*
  • Humans
  • Humidity*
  • Male
  • Marathon Running*
  • Middle Aged
  • Water


  • Water