Ice swimming and changes in body core temperature: a case study

INTRODUCTION 'Ice Mile' swimming is a new discipline in open-water swimming introduced in 2009. This case study investigated changes in body core temperature during preparation for and completion of two official 'Ice Miles', defined as swimming 1.609 km in water of 5°C or colder, in one swimmer. CASE DESCRIPTION One experienced ice swimmer (56 years old, 110.2 kg body mass, 1.76 m body height, BMI of 35.6 kg/m(2), 44.8% body fat) recorded data including time, distance and body core temperature from 65 training units and two 'Ice Miles'. DISCUSSION AND EVALUATION During training and the 'Ice Miles', body core temperature was measured using a thermoelectric probe before, during and after swimming. During trainings and the 'Ice Miles', body core temperature increased after start, dropped during swimming but was lowest during recovery. During training, body core temperature at start was the only predictor (ß = -0.233, p = 0.025) for the increase in body core temperature. Water temperature (ß = 0.07, p = 0.006) and body core temperature at start (ß = -0.90, p = 0.006) explained 61% of the variance for the non-significant decrease in body core temperature. Water temperature (ß = 0.077, p = 0.0059) and body core temperature at finish (ß = 0.444, p = 0.02) were the most important predictors for the lowest body core temperature. In 'Ice Miles', body core temperature was highest ~6-18 min after the start (38.3-38.4°C), dropped during swimming by 1.7°C to ~36.5°C and was lowest ~40-56 min after finish. The lowest body core temperature (34.5-35.0°C) was achieved ~100 min after start. CONCLUSIONS In an experienced ice swimmer with a high BMI (>35 kg/m(2)) and a high percent body fat (~45%), body core temperature decreased by 1.7°C while swimming and by 3.2-3.7°C after the swim to reach the lowest temperature in an official 'Ice Mile'. The swimmer suffered no hypothermia during ice swimming, but body core temperature dropped to <36°C after ice swimming. Future athletes intending to swim an 'Ice Mile' should be aware that a large body fat prevents from suffering hypothermia during ice swimming, but not after ice swimming.