Intermittent hand and forearm immersion in 20°C water attenuates thermal, cardiovascular, and perceptual strain in older adults during heat stress.

Adults >65 years of age experience deleterious health effects during extreme heat events at a greater rate than any other age cohort. The purpose of this study was to identify the effectiveness of acute intermittent hand and forearm (H+F) water immersion and/or chronic (7 week) folic acid supplementation on reducing thermal and cardiovascular strain in older adults during heat stress. Twelve older adults (six female; 65-89 years of age) were exposed to 2 h of heat stress at 34°C and 77% relative humidity during seated rest, with and without H+F immersion, following folic acid or placebo supplementation. During immersion trials, participants immersed both H+F in cool tap water (∼20°C) for 10 min at min 60 and 90. Core temperature, skin temperature and heart rate were monitored continuously, and blood pressure and the rate-pressure product were recorded every 10 min. Data were analysed as absolute changes and as a delta from min 50 (i.e., immediately before cooling). There was no effect of folic acid on any variable (all p > 0.05). Absolute and delta core temperature, skin temperature and heart rate increased over time (p ≤ 0.041); however, H+F water immersion attenuated this increase (p ≤ 0.046) after the first cooling bout. Likewise, absolute and delta RPP increased over time (p ≤ 0.047), but absolute RPP was attenuated with H+F water immersion (p = 0.003). These data suggest that intermittent H+F water immersion effectively attenuates thermal and cardiovascular strain for older adults at rest during heat stress.