Scheme 2.

Protocol of experiments. Subjects in the control group (placebo, 200 mL water) and the caffeine group (3 mg/kg body weight caffeine and 200 mL water) drank each solution at 30 min before heat loading (HL). HL was carried out by immersing half body into a hot water bath (42 ± 0.5 °C) for a total of 30 min with breaks for a total of 30 min. Automatic tympanic and local skin temperature measurements were conducted continuously at 10-s intervals for 60 min and then used to calculate mean body temperature. Pre, blood sampling at start of half body immersion; Post, blood sampling immediately after a total 60 min of heat loading procedure