The effect of age and mitigation strategies during hot water immersion on orthostatic intolerance and thermal stress

Abstract Hot water immersion improves cardiovascular health and sporting performance, yet its adverse responses are understudied. Thirteen young and 17 middle‐aged adults (n = 30) were exposed to 2 × 30 min bouts of whole‐body 39°C water immersion. Young adults also completed cooling mitigation strategies in a randomized cross‐over design. Orthostatic intolerance and selected physiological, perceptual, postural and cognitive responses were assessed. Orthostatic hypotension occurred in 94% of middle‐aged adults and 77% of young adults. Young adults exhibited greater dizziness upon standing (young subjects, 3 out of 10 arbitrary units (AU) vs. middle‐aged subjects, 2 out of 10 AU), with four terminating the protocol early owing to dizziness or discomfort. Despite middle‐aged adults being largely asymptomatic, both age groups had transient impairments in postural sway after immersion (P