Short-term Warm Water Immersion as a Heat Acclimation Strategy to Enhance Heat Dissipation in Older Adults: An Exploratory Study
Trial Snapshot
- Phase
- Not Applicable
- Status
- Completed
- Sponsor
- University of Ottawa
- Enrollment
- 12
- Locations
- 1
- Primary Endpoint
- Evaporative heat loss
Study Overview
Brief Summary
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).
Study Design
- Study Type
- Interventional
- Allocation
- Na
- Intervention Model
- Single Group
- Primary Purpose
- Basic Science
- Masking
- None
Masking Description
Data will be blinded prior to analysis.
Eligibility Criteria
- Ages
- 60 Years to 80 Years (Adult, Older Adult)
- Sex
- Male
- Accepts Healthy Volunteers
- Yes
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).
Arms & Interventions
Heat Acclimation
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.
Intervention: Heat acclimation (Other)
Outcomes
Primary Outcomes
Evaporative heat loss
Time Frame: End of 30 minute bout 3 (average of last 5 minutes).
Evaporative heat loss as assessed using a direct air calorimeter.
Whole-body heat loss
Time Frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
The sum of evaporative and dry heat exchange will be quantified during each exercise period (i.e., 150, 200 and 250 W/m2).
Evaporative heat loss
Time Frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Evaporative heat loss as assessed using a direct air calorimeter.
Evaporative heat loss
Time Frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Evaporative heat loss as assessed using a direct air calorimeter.
Whole-body heat loss
Time Frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
The sum of evaporative and dry heat exchange will be quantified during each exercise period (i.e., 150, 200 and 250 W/m2).
Whole-body heat loss
Time Frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
The sum of evaporative and dry heat exchange will be quantified during each exercise period (i.e., 150, 200 and 250 W/m2).
Secondary Outcomes
- Heart rate variability(End of 30 minute exercise bout 3 (average of last 5 minutes).)
- Core temperature(End of 30 minute exercise bout 3 (average of last 5 minutes).)
- Skin temperature(End of 30 minute exercise bout 3 (average of last 5 minutes).)
- Thermal comfort scale(End of 30 minute exercise bout 3 (average of last 5 minutes).)
- Thirst sensation scale(End of 30 minute exercise bout 3 (average of last 5 minutes).)
- Dry heat loss(End of 30 minute exercise bout 3 (average of last 5 minutes).)
- Thermal sensation scale(End of 30 minute exercise bout 3 (average of last 5 minutes).)
- Body heat content(Change from start to end of 30 minute exercise bout 2)
- Change in core temperature(Change from baseline resting to end of end of 30 minute exercise bout 3.)
- Heart rate(End of 30 minute exercise bout 3 (average of last 5 minutes).)
- Body heat storage(Change from start to end of 30 minute exercise bout 3)
- Cumulative body heat storage(Change from baseline resting to end of exercise bout 3)
- Change in skin temperature(Change from baseline resting to end of end of 30 minute exercise bout 3.)
- Rating of perceived exertion(End of 30 minute exercise bout 3 (average of last 5 minutes).)
- Body heat storage(Change from start to end of 30 minute exercise bout 1)
- Dry heat loss(End of 30 minute exercise bout 1 (average of last 5 minutes).)
- Dry heat loss(End of 30 minute exercise bout 2 (average of last 5 minutes).)
- Core temperature(End of 30 minute exercise bout 1 (average of last 5 minutes).)
- Core temperature(End of 30 minute exercise bout 2 (average of last 5 minutes).)
- Skin temperature(End of 30 minute exercise bout 1 (average of last 5 minutes).)
- Skin temperature(End of 30 minute exercise bout 2 (average of last 5 minutes).)
- Heart rate(End of 30 minute exercise bout 1 (average of last 5 minutes).)
- Heart rate(End of 30 minute exercise bout 2 (average of last 5 minutes).)
- Heart rate variability(End of 30 minute exercise bout 1 (average of last 5 minutes).)
- Heart rate variability(End of 30 minute exercise bout 2 (average of last 5 minutes).)
- Thermal comfort scale(End of 30 minute exercise bout 1 (average of last 5 minutes).)
- Thermal comfort scale(End of 30 minute exercise bout 2 (average of last 5 minutes).)
- Thermal sensation scale(End of 30 minute exercise bout 1 (average of last 5 minutes).)
- Thermal sensation scale(End of 30 minute exercise bout 2 (average of last 5 minutes).)
- Thirst sensation scale(End of 30 minute exercise bout 1 (average of last 5 minutes).)
- Thirst sensation scale(End of 30 minute exercise bout 2 (average of last 5 minutes).)
- Rating of perceived exertion(End of 30 minute exercise bout 1 (average of last 5 minutes).)
- Rating of perceived exertion(End of 30 minute exercise bout 2 (average of last 5 minutes).)
Investigators
Glen P. Kenny
Full Professor, University Research Chair, Principal Investigator
University of Ottawa