How Cold Is Too Cold? Reexamining The Safe Cold-water Temperature For Open Water Swimming

Open water swimming includes a degree of unpredictability that can directly affect athlete safety. If water temperature is cold, athletes will be at risk of hypothermia. Currently, for athlete safety purposes, World Aquatics mandates use of wetsuits during open water swimming at water temperatures ≤18 °C and for competition to be cancelled when water temperature is <16 °C. This competition cancelation threshold was established before the wetsuit mandate. Therefore, the safe cold-water threshold (defined as the critical cold-water temperature (Tcrit)) for open water swimming while wearing a wetsuit is unknown. PURPOSE: Test the hypothesis that Tcrit while wearing a wetsuit is below the currently mandated 16 °C water temperature threshold. METHODS: Twenty competitive swimmers (8 women) completed a constant workload cold-water swim in a flume while wearing a World Aquatics approved wetsuit. Swimming intensity was determined by matching heart rate to that observed during a self-paced 3 km swim. During the experimental trial, water temperature was initially set at ~16 °C and progressively decreased to a minimum of ~13 °C. Core (rectal) temperature was continuously recorded. Every 30 minutes, oxygen uptake and RER were measured via open circuit indirect calorimetry and used to estimate metabolic heat production (Hprod). Tcrit was defined as the water temperature at which core temperature began to decrease, as determined by segmental regression. Hprod was analyzed during the initial 30 min and final 30 min of the trial. Pearson correlations were used to compare associations between Log10Tcrit and anthropometric variables. RESULTS: Tcrit was lower than 16 °C (15.1 °C, 95% CI: 14.7 °C to 15.3 °C, p < 0.0001). Tcrit did not differ between men (15.2 °C, 95% CI: 14.8 °C to 15.5 °C) and women (15.1 °C, 95% CI: 14.4 °C to 15.7 °C; p = 0.9692). There were no differences in Hprod, when comparing the initial (484 ± 61 W/m2) and final (472 ± 61 W/m2; p = 0.5680) 30 min of the trial. No association between Log10Tcrit and anthropometric variables reached statistical significance. However, initial Hprod approached statistical significance (r = -0.428; p = 0.0671). CONCLUSION: The safe cold-water temperature threshold for open water swimming while wearing a wetsuit is lower than 16 °C and does not differ between men and women. Support: World Aquatics Supported by: World Aquatics