Hyperthermia during open water swimming: risks, monitoring and mitigation strategies.

Purpose: The environmental conditions in open water swimming (OWS) can impair thermoregulation. Here we explored and discussed four interrelated topics concerning the disruption of thermal homeostasis, in parallel with the underlying physiological mechanisms, during OWS competitions in hot climates: (i) potential health risks; (ii) possible impacts on performance; (iii) technical feasibility of core temperature (Tc) measurement; and (iv) cooling strategies applicable to this context.

Methods: An integrative review was conducted. A systematic search of PubMed, SCOPUS, EMBASE, and Web of Science was performed, yielding 4610 studies. After screening and excluding duplicates, 42 studies underwent full-text review, resulting in 20 studies included.

Results: Water temperatures (Tw) close to the upper limit established by World Aquatics (31 °C) negatively affect performance and increase health risks for open water swimmers. Thermal stress during competitions, caused by prolonged exposure to hot water, impairs thermoregulation, leading to dehydration, increased Tc, and cardiovascular strain. Cooling strategies such as pre-cooling and per-cooling showed potential to mitigate heat strain, although their application in open water swimming events remains challenging due to logistical constraints. Modern strategies of post-cooling have been primarily designed for pre-hospital or emergency care settings. Wearable technologies for real-time Tc monitoring emerged as a promising tool for improving athlete safety and performance management during competitions.

Conclusion: The rise in Tc during open water swimming in hot water is a worrying phenomenon caused by impaired cooling mechanisms, is exacerbated by prolonged exposure to solar radiation, and negatively impacts performance and increases health risks. Cooling strategies such as pre-cooling and per-cooling are key strategies to mitigate heat strain. Wearable physiological monitoring now allows for better modeling of individual thermophysiological profiles, improving both competitive strategies and safety.