Analysis of Factors Associated With Continued Cooling of Core Temperature After Prolonged Cold-Water Swimming

To assess the factors associated with continued cooling duration of core temperature (Tcore°) after prolonged outdoor cold-water swimming.

We designed a cohort study among swimmers participating in an outdoor cold-water swim during qualifying for the English Channel Swim. The day before the event, the participants completed a demographic questionnaire, and body composition was measured using bioelectrical impedance analysis (mBCA 525, Seca). The swimming event consisted of laps over a 1000-m course, for up to 6 hours, in water at 12.5 to 13 °C. Tcore° was measured using an ingestible temperature sensor (e-Celsius, BodyCap) during and up to 1 hour after the swim.

A total of 14 participants (38 [11] y; N = 14, n = 11 males, n = 8 in swimming costume and n = 6 in wetsuit) were included. Before swimming, Tcore° was 37.54 (0.39) °C. The participants swam for an average of 194.00 (101.94) minutes, and mean Tcore° when exiting the water was 35.21 (1.30) °C. The duration of continued cooling was 25 (17) minutes with a minimum Tcore° of 34.66 (1.26) °C. Higher body mass index (r = .595, P = .032) and fat mass (r = .655, P = .015) were associated with longer continued cooling, independent of wetsuit wear. Also, the rate of Tcore° drop during swimming (-1.22 [1.27] °C/h) was negatively correlated with the rate of Tcore° gain after swimming (+1.65 [1.23] °C/h, r = -.682, P = .007).

Increased body mass index and fat mass were associated with Tcore° continued cooling duration after prolonged outdoor cold-water swimming at 12.5 to 13 °C. The rate of Tcore° drop during swimming was negatively correlated with the rate of rewarming.