Influence of Sex on Whole-Body Heat Exchange Following Cold Beverage Ingestion During Work-Rest Cycles in the Heat

Consuming cold beverages during work in the heat can reduce sweat output in males. However, responses in females may differ given sex-related differences in whole-body heat exchange during work in the heat. We therefore assessed whether sex influences whole-body heat exchange following cold beverage ingestion during intermittent work in hot conditions.

Twenty young adults (ten females, mean ± SD: 23 ± 3 years) performed four 15-min bouts of moderate-intensity cycling at a fixed rate of metabolic heat production (200 W·m^-2), each interspersed by 15-min rest periods in dry heat (40°C, ~12% relative humidity). On separate days, participants ingested either ice-slurry (~0°C), standardized to provide a heat transfer capacity of 75 kJ·m^-2, or an identical mass of warm fluid (37.5°C) prior to the first and third exercise bouts. Dry and evaporative heat exchange (direct calorimetry), as well as metabolic heat production (indirect calorimetry), were measured continuously and used to determine cumulative heat storage (summation of heat loss and heat gain) over the entire protocol.

Dry and evaporative heat exchange were unaffected by beverage condition or sex (all p > 0.05). Relative to warm fluid, ice-slurry ingestion reduced cumulative heat storage in females (86 ± 120 vs. 167 ± 103 kJ, p = 0.01) and males (69 ± 181 vs. 216 ± 94 kJ) but responses did not differ between sexes (p = 0.70).

Whole-body heat exchange was unaffected by beverage temperature, albeit the heat transfer to the ingested ice-slurry reduced cumulative heat storage in both sexes during intermittent work in dry heat.