BACKGROUND: Heatwave-related morbidity and mortality are disproportionately higher in older females than in other population groups. This elevated vulnerability may reflect sex-specific reductions in heat-loss capacity, further compounded by age- and chronic disease-related impairments in heat dissipation. Recent work demonstrated that seven days of 60-minute warm-water immersion enhanced heat-loss capacity and reduced cardiovascular strain by 20% in older males during exercise-heat stress (PMID: 39820413). Whether passive, short-term heat acclimation achieved through warm-water immersion may offer similar benefits for older females, thereby potentially mitigating the physiological strain of prolonged heat exposure, remains unknown. HYPOTHESIS: We evaluated the hypothesis that seven days of passive heat acclimation, achieved through warm-water immersion would reduce thermal and cardiovascular strain in older females during subsequent prolonged heat exposure. METHODS: Ten older females (mean SD age: 72 4 y) completed seven consecutive days of warm-water immersion of ~120 min/day at ~39°C, during which core (rectal) temperature (Tcore) was clamped at ~38.5°C for the final 60 minutes. Participants underwent a standardized daylong indoor overheating exposure(8-h at 36°C, 45% relative humidity) in an environmental chamber both before (Day 0) and after (Day 8) of the heat-acclimation protocol. Tcore, heart rate, and skin temperature (Tsk) were measured continuously. Outcomes were analyzed with linear mixed models for total exposure (corrected for baseline) and area-under-the -curve (AUC) differences between days. RESULTS: Baseline Tcore, heart rate, and Tsk did not differ between days (all P > 0.48). During the heat exposure, Tcore was 0.2°C lower on Day 8 compared with Day 0 95% CI: 0.1, 0.2; P < 0.001, and Tsk was 0.2°C lower 0.1, 0.3; P < 0.001. AUC analyses confirmed reductions in Tcore (1.7°C·h 0.7, 2.6; P = 0.0043) and Tsk (1.2°C·h 0.3, 2.1; P = 0.019). Heart rate decreased by 3 beats/min 2, 4; P < 0.001, although the AUC corresponding difference were not statistically significant (P = 0.17). CONCLUSION: These preliminary findings indicate that short-term warm-water immersion elicits beneficial physiological adaptations in older females, reducing both thermal and cardiovascular strain during prolonged heat exposure. While such heat-acclimation strategies could be adapted for home use, their safe implementation would require initial supervision and should be further validated in larger future studies to inform practical adoption. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Li-Maloney et al. (Fri,) studied this question.