Hot Water Immersion as a Heat Acclimation Strategy in Older Adults
- Conditions
- Heat ExposureThermoregulationHeat StressAgingHyperthermia
- Interventions
- Other: Heat acclimation
- Registration Number
- NCT05838612
- Lead Sponsor
- University of Ottawa
- 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).
- Detailed Description
Not available
Recruitment & Eligibility
- Status
- COMPLETED
- Sex
- Male
- Target Recruitment
- 12
- 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.
- Heat adapted due to repeated exposure to hot environments within the last 3 weeks (use sauna, recent travel to hot climates, other).
Study & Design
- Study Type
- INTERVENTIONAL
- Study Design
- SINGLE_GROUP
- Arm && Interventions
Group Intervention Description Heat Acclimation 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.
- Primary Outcome Measures
Name Time Method Evaporative heat loss 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 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).
- Secondary Outcome Measures
Name Time Method Core temperature End of 30 minute exercise bout 3 (average of last 5 minutes). Core temperature indexed by rectal/visceral temperature
Skin temperature End of 30 minute exercise bout 3 (average of last 5 minutes). Skin temperature measured at 4-sites (chest, upper arm, thigh, calf) with mean value calculated as weighted value of 4 sites - upper arm, 30%; chest, 30%; thigh, 20%; and calf, 20%.
Thermal comfort scale End of 30 minute exercise bout 3 (average of last 5 minutes). Thermal comfort assessed via a questionnaire using the ASHRAE 4-point scale ("1=comfortable to 4=very uncomfortable")
Thirst sensation scale End of 30 minute exercise bout 3 (average of last 5 minutes). Thirst sensation will be quantified using a 9-point scale ("1=not thirsty at all to 9=very, very thirsty")
Dry heat loss End of 30 minute exercise bout 3 (average of last 5 minutes). Dry heat loss as assessed using a direct air calorimeter.
Thermal sensation scale End of 30 minute exercise bout 3 (average of last 5 minutes). Thermal sensation will be assessed using the ASHRAE 7-point scale ("0=neutral to 7=extremely hot")
Body heat content Change from start to end of 30 minute exercise bout 2 Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.
Change in core temperature Change from baseline resting to end of end of 30 minute exercise bout 3. Core temperature indexed by rectal/visceral temperature
Heart rate End of 30 minute exercise bout 3 (average of last 5 minutes). Measured continuously with chest-band device
Rating of perceived exertion End of 30 minute exercise bout 3 (average of last 5 minutes). Rating of perceived exertion will be quantified using a 14-point scale ("6=no exertion at all to 20=maximal exertion")
Body heat storage Change from start to end of 30 minute exercise bout 3 Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.
Heart rate variability End of 30 minute exercise bout 3 (average of last 5 minutes). Measures of variability computed from the time, frequency, time-frequency, scale-invariant, entropy, and other nonlinear domains
Cumulative body heat storage Change from baseline resting to end of exercise bout 3 Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.
Change in skin temperature Change from baseline resting to end of end of 30 minute exercise bout 3. Skin temperature measured at 4-sites (chest, upper arm, thigh, calf) with mean value calculated as weighted value of 4 sites - upper arm, 30%; chest, 30%; thigh, 20%; and calf, 20%.
Trial Locations
- Locations (1)
Univerisity of Ottawa
🇨🇦Ottawa, Ontario, Canada