Individual variation in thermal responses of clothed women and men during repeated short-term cold-water immersions

Sudden immersion in cold water, resulting in a rapid and intense skin temperature drop, initiates physiological stress reactions collectively known as the ‘cold shock’ response. The aim of the present study was to investigate individual variations in body core and skin temperature responses induced by repeated short-term immersions of clothed subjects in cold water. Four medically screened healthy women aged 25–30 years and four men aged 23–28 years volunteered for the study. Each subject was immersed three times in cold water (4°C) wearing a water-permeable winter combat clothing ensemble weighing about 5.6 kg and which prior to immersion, had a thermal insulation of about 1.7 clo. The immersions took place at the same time of day, at intervals of at least a week. The subjects were continuously monitored by an ECG as a safety precaution. Rectal (Tre) and skin temperatures at 13 sites were also monitored continuously and registered every minute, and mean skin temperature (Tsk) was calculated as a weighted mean. The intra-individual pre-immersion Tre ranged, on different days, from 0.10 to 0.69°C in women and from 0.20 to 0.75°C in men; the Tsk ranged from 0.5 to 2.5°C and from 0.2 to 1.2°C, respectively. No significant individual differences in Tre changes were observed between immersions, which resulted in an average (±SD) Tre drop of only 0.04±0.11°C in women and men. Pre-immersion Tre had no effect on Tsk responses. The average individual pre-immersion Tsk varied between 27.8 and 32.1°C in women, and between 32.8 and 34.1°C in men, whilst the average drop in Tsk was 15.3±1.8°C and 17.5±0.9°C, respectively. The drop in intra-individual Tsk ranged, on different days, from 1.3 to 3.0°C in women and from 0.3 to 1.8°C in men. The body temperature responses of each immersed individual (clothed) were reproducible in short-term repeated cold-water immersions, regardless of the pre-immersion Tre or Tsk. No effects of adaptation were found in body temperature responses.