To investigate the efficacy of heat acclimation (HA) in the young (YEX) and elderly (EEX) following exercise-HA, and the elderly utilising post-exercise hot water immersion HA (EHWI).

Cross-sectional study.

Twenty-six participants (YEX: n=11 aged 22±2 years, EEX: n=8 aged 68±3 years, EHWI: n=7 aged 73±3 years) completed two pre/post-tests, separated by five intervention days. YEX and EEX exercised in hot conditions to raise rectal temperature (Trec) ≥38.5°C within 60 min, with this increase maintained for a further 60 min. EHWI completed 30 min of cycling in temperate conditions, then 30 min of HWI (40°C), followed by 30 min seated blanket wrap. Pre and post-testing comprised 30 min rest, followed by 30 min of cycling exercise (3.5 W.kg-1 Ḣprod), and a six-minute walk test (6MWT), all in 35°C, 50% RH.

The HA protocols did not elicit different mean heart rate (HR), Trec, and duration Trec ≥38.5°C (p>0.05) between YEX, EEX, and EHWI groups. Resting Trec, peak skin temperature, systolic and mean arterial pressure, perceived exertion and thermal sensation decreased, and 6MWT distance increased pre to post HA (p<0.05), with no difference between groups. YEX also demonstrated a reduction in resting HR (p<0.05). No change was observed in peak Trec or HR, vascular conductance, sweat rate, or thermal comfort in any group (p>0.05).

Irrespective of age or intervention, HA induced thermoregulatory, perceptual and exercise performance improvements. Both exercise-HA (EEX), and post-exercise HWI (EHWI) are considered viable interventions to prepare the elderly for heat stress.