A characterisation of elite open water swimmers' core temperature responses and preparation practices in European...

Open water swimming competition occurs within a water temperature (Tw) range (World Aquatics Tw: 16-31 °C) where heat- (hyperthermia) and cold-related (hypothermia) medical events and race-dropouts regularly occur. These can be attributed to the thermodynamic properties of water and human thermoregulatory (Treg) maladaptations for submersion [modest deviations (±0.5-2 °C) in core temperature (Tc) can impair performance and health]. Additionally, little real-world knowledge regarding elite open water swimmer preparation [e.g., heat/cold acclimation/acclimatisation] for extreme environments is available. Thus, elite swimmers' Tc and preparation practices were characterised during open water swimming competition.

(i) Characterise Tc responses; and (ii) questionnaire preparation practices of elite swimmers within cold and warm Tw European Aquatics open water swimming competitions.

Tc data were characterised (ingestible-telemetry) for 50 (20 female) elite swimmers during the 2023-25 European Aquatics Open Water Swimming Cup (Leg 4 - COLD₁, Leg 1 - COLD₂, Leg 5 - COLD₃, Leg 1 - COLD₄) and the 2023 Junior European Aquatics Open Water Swimming Championships (WARM). A pre- and post-race questionnaire was disseminated to survey training/preparation practices and symptomology in-race.

Tc responses were highly variable [maximum ± Tc °C change: COLD₁ (+1.2 °C; -2.0 °C), COLD₂ (+1.2 °C; -1.6 °C), COLD₃ (+1.7 °C; -1.3 °C), COLD₄ (+2.2 °C; -4.2 °C), WARM (+1.8 °C; -1.7 °C)]. Mild and/or hypo/hyper-thermia co-presented within the same race. Tc in-race was not associated with race time, nor ranking (P ≥ .080). Heat/cold acclimation/acclimatisation adoption was not associated with lower likelihood of hypo-/hyper-thermia (P ≥ .184), nor cold/heat-related symptomology in-race (P ≥ .837).

The observed variability in Tc responses, alongside co-presentation of mild and/or hyper-/hypo-thermia in-race surfaces the challenges to protect open water swimmers' health and performance during competition. Whilst heat/cold acclimation/acclimatisation and body temperature manipulation (e.g., cooling/heating) interventions may be helpful, there is a paucity of open water swimming specific data to evidence-inform practice.