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.