Abstract
This project studied the effects of regional body composition on the core temperature responses to water immersion. Forty-six volunteers participated in the study, with subgroups of eighteen immersed from the neck down in 18, 22, and 26°C water for up to 10 h, respectively. Regional body composition was measured by Dual-energy X-ray Absorptiometry. Rectal temperature (Tc), and 10-site mean skin temperatures (Tsk) were measured every minute. Immersion durations ranged from 0.83 to 10 h, and Tc ranged from 35.2 to 38.0°C at the end of immersion. Tc cooling rates were calculated over the first 0.83 h of immersion. Tc cooling rates varied widely, ranging from -0.37 to 0.93°C/h, -0.39 to 1.87°C/h, and -0.13 to 1.13°C/h at 18, 22 and 26°C water, respectively. The trunk fat mass was negatively and significantly correlated to Tc cooling rates (-0.58, -0.76, 0.60, -0.64, p ≤ 0.01) at 18, 22, 26°C water and across all temperatures combined. The arm fat mass, fat percentage and surface-to-mass ratio were negatively and significantly correlated with Tc cooling rates at most conditions, but not all. Individuals with high cooling rates (≥0.6°C/h) had on average half the trunk fat mass of those with low cooling rates (≤0.25°C/h), and those with low trunk fat mass are least capable of defending core body temperature.