Four-Days of Passive Heat Acclimation Increases Exercise Capacity in Healthy Older Adults Living in the UK

Background: Older adults are particularly vulnerable to heat related illness due to impaired thermoregulatory responses. Heat acclimation (HA) strategies can mitigate the negative impacts of high environmental temperatures on physiological and perceptual responses. Whilst active HA strategies may prove problematic for older adults, passive approaches such as hot water immersion (HWI) may be more feasible. Methods: This study investigated the effects of four consecutive days of HWI on physiological and perceptual markers in individuals aged over 65 years during moderate exercise. Nine healthy, recreationally active participants (76 ± 5 years) completed two 30 min cycling bouts at 75-80% age predicted HR_max pre- and post-four days of HWI at 40 °C. Measures of average HR, gastrointestinal temperature, skin temperature, thermal sensation, thermal comfort, rate of perceived exertion, power output, and distance covered were recorded during both exercise bouts. Results: Results showed a significant increase in exercise capacity as measured by power output (p < 0.05, 7.45 W) post-intervention, despite no change in ratings of perceived exertion, and reductions in average heart rate (112 ± 3 vs. 109 ± 4 bpm). There were no alterations in gastrointestinal or skin temperature, and ratings of thermal comfort and sensation remained unchanged post-intervention. Conclusions: These preliminary findings provide important new evidence that four days of passive HWI may be a practical and effective method of inducing physiological adaptations in older individuals, which may be of use in interventions to mitigate the negative impact of high environmental temperatures in this population.