Thermal sensation and substrate utilization differs among low- and high-fat women exposed to 17°C water

Abstract

Thermal sensation and the physiological responses of women (follicular phase) exposed to 17 degrees C immersion for 120 minutes were investigated. The subjects were divided into 2 groups by percent body fat (low fat [LF] = 21% +/- 2% [mean +/- SD] vs high fat [HF] = 30% +/- 3%). A 2-way analysis of variance was used to determine differences between the groups in metabolism, metabolism derived from carbohydrate, metabolism derived from fat, blood glucose, rectal temperature, skin temperature, and thermal sensation. As anticipated, pooled metabolism increased across the 120-minute immersion. Metabolism derived from carbohydrate was significantly higher in the LF than in the HF group and increased across time. Blood glucose decreased significantly across time, yet there was no group difference, suggesting that the LF group may have utilized a greater proportion of intramuscular glycogen. The HF group demonstrated a higher rectal temperature compared to their LF counterparts. Overall, rectal temperature demonstrated a group x time interaction as immersion continued. However, rectal temperature for all subjects remained above 35 degrees C. Surprisingly, the HF group perceived significantly greater thermal discomfort than did their LF counterparts. Since intramuscular glycogen utilization is associated with shivering thermogenesis, the suspected greater utilization of this fuel by the LF group may have contributed to less thermal discomfort than in the HF group. However, since glycogen utilization was not directly measured, this speculation cannot be validated. It is also possible that the modified thermal sensation scale we used may not be an adequate marker of thermal discomfort in females with a high percentage of body fat (28% to 35%) exposed to cold water immersion.