The influence of various methods of fluid ingestion on changes in selected physiological reactions during thermal stress in a sauna

Abstract

Abstract The purpose of this experiment was to compare the influence of three different methods of fluid ingestion on selected physiological reactions during passive heating in a sauna. The participants were divided into three groups: group I (n=10) consumed a 4% glycerol solution (an average of 1860 ml) before entering the sauna; group II (n=10) consumed a nonrestricted amount of mineral water (an average of 1470 ml) whilst staying in, the sauna; group III (n=10) consumed 750 ml of water before night rest plus 750 ml of water prior to entering the sauna. The control group consisted of all participants (n=30) engaged in a one-time sauna exposure without consuming any fluids before or during the sauna session. Each sauna exposure involved a total time of 49 min: 3×15 min, of thermal heating in the sauna (95°C; relative humidity 26%), with two 2-min breaks for cooling. The lowest increases in rectal temperature and heart rate, as well as the smallest decrease of plasma volume were noted in subjects consuming water during the thermal exposure. The thermal sensations were also less pronounced during the heat exposure in this group. This data indicates that this system of hydration is likely to contribute to a more effective body heat elimination and better cardiac system functioning during the thermal exposition.