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ObjectivesTo provide a rationale for minimum water temperature rules for elite and subelite marathon swim racing and highlight factors that make individuals vulnerable to excessive cooling during open water swimming.Methods12 lean competitive swimmers swam for up to 2 hours, three times in different water temperatures between 14°C and 20°C, wearing standard swimming costumes and hats. Rectal temperature (Tre), oxygen consumption, perception of cold and performance were measured.ResultsIn 16°C, half the swimmers did not complete a 2-hour swim; four became (or were predicted to become) hypothermic within 2 hours. In 18°C, three-quarters completed the swim; three became (or were predicted to become) hypothermic. In 20°C, one swimmer was predicted to become hypothermic in under 2 hours. The mean linear rate of fall of Tre was greater in 16°C (−1.57°C/hour) than 18°C (−1.07°C/hour) (p=0.03). There was no change in swimming performance during the swims or between conditions. Most of the cooling rate could be explained by metabolic heat production and morphology for both 16°C (R2=0.94, p<0.01) and 18°C (R2=0.82, p<0.01) conditions. No relationship was observed between Tre and perception of thermal sensation (r=0.25, p=0.13), and there was a weak correlation between Tre and thermal comfort (r=0.32, p=0.04).ConclusionWe recommend that 16°C and 18°C water are too cold for elite marathon swim racing. FédérationInternationale de Natation rules were changed in 2017 to make wetsuits compulsory below 18°C and optional below 20°C.

Issues remaining include (1) marked differences in the definitions, terminology, and data collection methods used by local, national, and international agencies [5,6] and (2) lack of consistent bilateral communication of drowning data between prevention, rescue, and life-support services and downstream care entities. [...]by specifying unambiguous definitions of triggers, actions, and interventions, it provides the necessary tools for a more effective deployment of resources; better coordination between all drowning prevention, rescue, and treatment actors; the establishment of adequate prevention strategies; and for the measurement of future cost-benefit ratios related to outcomes in terms of public health, financial, political, and social impacts.

Low water temperature (<15 °C) has been faced by many organizers of triathlons and swim-runs in the northern part of Europe during recent years. More knowledge about how cold water affects athletes swimming in wetsuits in cold water is warranted. The aim of the present study was therefore to investigate the physiological response when swimming a full Ironman distance (3800 m) in a wetsuit in 10 °C water. Twenty triathletes, 37.6 ± 9 years (12 males and 8 females) were recruited to perform open water swimming in 10 °C seawater; while rectal temperature (Tre) and skin temperature (Tskin) were recorded. The results showed that for all participants, Tre was maintained for the first 10–15 min of the swim; and no participants dropped more than 2 °C in Tre during the first 30 min of swimming in 10 °C water. However; according to extrapolations of the results, during a swim time above 135 min; 47% (8/17) of the participants in the present study would fall more than 2 °C in Tre during the swim. The results show that the temperature response to swimming in a wetsuit in 10 °C water is highly individual. However, no participant in the present study dropped more than 2 °C in Tre during the first 30 min of the swim in 10 °C water.