Figure 1.

Overview of experimental protocol. Healthy young (n = 20) and older (n = 20) participants were exposed to two 3-h extreme heat exposures on different days: 1) DRY (47°C and 15% humidity) and 2) HUMID (41°C and 40% humidity). To mimic heat generation comparable with activities of daily living, participants performed seven 5 min bouts of light physical activity (∼3 METs) dispersed throughout the heat exposure. Participants consumed 3 mL/kg body mass of tap temperature water (14°C–16°C) every hour during the heat exposures. Measurements included core and skin temperatures, heart rate, blood pressure, local and whole body sweat rate, forearm blood flow, plasma osmolality, change in plasma volume, and perceptual responses.