Hot Water Immersion as a Heat Acclimation Strategy in Older Adults

University of Ottawa

Status: Completed

Conditions: Aging; Heat Exposure; Thermoregulation; Heat Stress; Hyperthermia

Treatments: Other: Heat acclimation

Study type: Interventional

Funder types: Other

Identifiers

NCT05838612

HEPRU-2023-02

Details and patient eligibility

About

Aging is associated with impairments in heat loss responses of skin blood flow and sweating leading to reductions in whole-body heat loss. Consequently, older adults store more body heat and experience greater elevations in core temperature during heat exposure at rest and during exercise. This maladaptive response occurs in adults as young as 40 years of age. Recently, heat acclimation associated with repeated bouts of exercise in the heat performed over 7 successive days has been shown to enhance whole-body heat loss in older adults, leading to a reduction in body heat storage. However, performing exercise in the heat may not be well tolerated or feasible for many older adults. Passive heat acclimation, such as the use of warm-water immersion may be an effective, alternative method to enhance heat-loss capacity in older adults. Thus, the following study aims to assess the effectiveness of a 7-day warm-water immersion (~40°C) protocol in enhancing whole-body heat loss in older adults. Warm-water immersion will consist of a one-hour immersion in warm water with core temperature clamped at 38.5°C. Improvements in whole-body heat loss will be assessed during an incremental exercise protocol performed in dry heat (i.e., 40°C, ~15% relative humidity) prior to and following the 7-day passive heat acclimation protocol. The incremental exercise protocol will consist of three 30 minute exercise bouts performed at increasing fixed rates of metabolic heat production (i.e., 150, 200, and 250 W/m2), each separated by 15-minutes of recovery, with exception final recovery will be 1-hour in duration) performed in a direct calorimeter (a device that provides a precise measurement of the heat dissipated by the human body).

Enrollment: 12 patients

Sex: Male

Ages: 60 to 80 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• Elderly (60-80 years), non-smoking adults.
• Not engaged in regular physical activity (>2 sessions/week for ≥20 minutes per session).
• Willing to provide informed consent.
• Healthy, no diagnosed health conditions.
• Body Mass index (BMI) <35 kg/m2.

Exclusion criteria

• Heat adapted due to repeated exposure to hot environments within the last 3 weeks (use sauna, recent travel to hot climates, other).

Trial design

Primary purpose: Basic Science

Allocation: N/A

Interventional model: Single Group Assignment

Masking: None (Open label)

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12 participants in 1 patient group

Heat Acclimation

Experimental group

Description:

Participants will undergo an exercise heat stress test prior to and following seven consecutive days of warm-water immersion (\~40°C) of 1-hour duration with core temperature clamped at 38.5°C. During the exercise-heat stress test participants will perform three, successive 30-minute bouts of semi-recumbent cycling performed at increasing fixed loads of metabolic heat production of 150, 200 and 250 W/m2 (i.e., exercise bout 1, exercise bout 2 and exercise bout 3, respectively), each separated by 15-minute of rest break with the final recovery extended to 1-hour.

Treatment:

Other: Heat acclimation