Mitigating Heat-induced Physiological Strain and Discomfort in Older Adults Via Lower Limb Immersion and Neck Cooling

The incidence and severity of hot weather and extreme heat events (heat waves) is increasing. As such, there is an urgent need to develop heat-alleviation strategies that can provide targeted protection for older adults who are at an elevated risk for heat-induced illnesses or death due to impaired body temperature and cardiovascular regulation. While air-conditioning provides the most effective protection from extreme heat, it is inaccessible for many individuals and cannot be used during power outages (e.g., heat-related rolling blackouts). Immersion of the lower limbs in cold water and/or the application of cold towels to the neck have been recommended as simple and sustainable alternatives to air-conditioning. However, empirical data to support the efficacy of these interventions for mitigating physiological strain and discomfort in older adults is lacking. To address this knowledge gap, this randomized crossover trial will evaluate the effect of lower limb immersion with and without application of cold towels to the neck on body core temperature, cardiovascular strain and autonomic function, dehydration, and thermal comfort in adults aged 65-85 years exposed to simulated heat wave conditions (38°C, 35% relative humidity) for 6 hours.

Inclusion Criteria:Male or female adults.Aged 65-85 years.Non-smoking.English or French speaking.Ability to provide informed consent.Exclusion Criteria:Physical restriction (e.g., due to disease: intermittent claudication, renal impairment, active proliferative retinopathy, unstable cardiac or pulmonary disease, disabling stroke, severe arthritis, etc.).Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable (e.g., medications increasing risk of heat-related illness; beta blockers, anticholinergics, etc.)Cardiac abnormalities identified via 12-lead ECG during an incremental exercise test to volitional fatigue (performed for all participants).Peak aerobic capacity (VO2peak), as measured during an incremental exercise test to volitional fatigue, exceeding the 50th percentile of age- and sex-specific normative values published by the American College of Sports Medicine (ACSM).