Safe Cold-Water Thresholds while Wearing Wetsuits Approved for Open Water Swimming Competitions

This study tested the hypothesis that the critical cold-water temperature (T crit ) in which core temperature can no longer be maintained while wearing an approved wetsuit is below the currently mandated water temperature of 16°C. We further aimed to examine the effect of wetsuit sleeves on T crit . We recruited twenty trained swimmers (12 men, 8 women) who completed 120 min progressive cooling swim trials in a swim flume. Water temperature at the start was 16°C and decreased ~0.15°C every 10 minutes while swimming at race-representative intensity and wearing a full-length wetsuit. A subset (n=8) completed an additional swim trial comparing sleeved vs. sleeveless wetsuits. The water temperature upon which core temperature could not be maintained (i.e., T crit ) was identified using segmental linear regression. Median T crit was 15.0°C (95% CI: 14.8-15.3°C), significantly below the 16°C regulation (p<0.001). No differences in T crit were observed between genders (p=0.78; men: 15.0°C (95% CI: 14.6-15.3°C); women: 14.91°C (95% CI:14.6-15.4°C)) or wetsuit types (p=0.90; sleeved: 15.1 ± 0.5°C); sleeveless: 15.1 ± 0.6°C). Multiple regression analysis revealed that body fat percentage (beta coefficient−0.06088: p = 0.0390), metabolic heat production (beta coefficient: −0.004416; p=0.0079), and body surface area-to-mass ratio (beta coefficient: −370.6; p=0.0078) significantly explained T crit (R²=0.41, p=0.008). While our data demonstrate that trained swimmers can physiologically tolerate temperatures below current regulations, we recommend maintaining the 16°C mandate to provide appropriate safety margins for the diverse competitive population and variable real-world conditions encountered in open water swimming competitions.