Physiological Effects of Consecutive Days of Heat Exposure with Different Overnight Cooling Conditions in Older Men

What This Trial Is About

Extreme heat events are increasing in frequency and intensity, which raises the risk of heat-related illnesses for workers exposed to hot environments. Current heat-stress guidelines focus on limiting core body temperature rises during work and assume recovery in cool indoor settings. However, many workers recover overnight in overheated places without air conditioning, which may increase physiological strain and reduce heat tolerance on following workdays, especially in older adults who have reduced heat-loss ability. The effects of such overnight recovery conditions on repeated heat exposure responses are not well understood. This study evaluates how overnight recovery temperatures affect physiological strain during two consecutive days of simulated moderate-intensity occupational heat exposure in healthy older men aged 50 to 75. Participants complete daytime work sessions in a hot environment 37.5C, 35% relative humidity followed by overnight recovery in either the recommended indoor temperature limit of 26C 45% relative humidity or an overheated environment at 31C 45% relative humidity. The study uses a crossover design where each participant experiences both recovery conditions. During the study, researchers measure core temperature, cardiovascular strain, heat-loss capacity, hydration, sleep quality, cognitive function, mood, and perceived exertion throughout the exposure protocol. Whole-body heat-loss is assessed before and after the heat exposure. Data collection includes physiological monitoring during work and overnight recovery, plus assessments of mood, cognition, and sleep on multiple days. The total participation spans two days and nights of heat exposure with detailed monitoring to understand how overnight cooling affects responses to repeated heat stress.

Consecutive Occupational Heat Exposure With and Without Overnight Cooling