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 Type
INTERVENTIONAL
Allocation
NA
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
12
Participants will complete a 7-day passive heat acclimation protocol consisting of immersion in warm water (\~40°C) for 1 hour over 7 consecutive days.
Univerisity of Ottawa
Ottawa, Ontario, Canada
Evaporative heat loss
Evaporative heat loss as assessed using a direct air calorimeter.
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Evaporative heat loss
Evaporative heat loss as assessed using a direct air calorimeter.
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Evaporative heat loss
Evaporative heat loss as assessed using a direct air calorimeter.
Time frame: End of 30 minute bout 3 (average of last 5 minutes).
Whole-body heat loss
The sum of evaporative and dry heat exchange will be quantified during each exercise period (i.e., 150, 200 and 250 W/m2).
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Whole-body heat loss
The sum of evaporative and dry heat exchange will be quantified during each exercise period (i.e., 150, 200 and 250 W/m2).
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Whole-body heat loss
The sum of evaporative and dry heat exchange will be quantified during each exercise period (i.e., 150, 200 and 250 W/m2).
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Body heat storage
Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.
Time frame: Change from start to end of 30 minute exercise bout 1
Body heat content
Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.
Time frame: Change from start to end of 30 minute exercise bout 2
Body heat storage
Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.
Time frame: Change from start to end of 30 minute exercise bout 3
Cumulative body heat storage
Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.
Time frame: Change from baseline resting to end of exercise bout 3
Dry heat loss
Dry heat loss as assessed using a direct air calorimeter.
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Dry heat loss
Dry heat loss as assessed using a direct air calorimeter.
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Dry heat loss
Dry heat loss as assessed using a direct air calorimeter.
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Core temperature
Core temperature indexed by rectal/visceral temperature
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Core temperature
Core temperature indexed by rectal/visceral temperature
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Core temperature
Core temperature indexed by rectal/visceral temperature
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Change in core temperature
Core temperature indexed by rectal/visceral temperature
Time frame: Change from baseline resting to end of end of 30 minute exercise bout 3.
Skin temperature
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%.
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Skin temperature
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%.
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Skin temperature
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%.
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Change in skin temperature
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%.
Time frame: Change from baseline resting to end of end of 30 minute exercise bout 3.
Heart rate
Measured continuously with chest-band device
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Heart rate
Measured continuously with chest-band device
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Heart rate
Measured continuously with chest-band device
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Heart rate variability
Measures of variability computed from the time, frequency, time-frequency, scale-invariant, entropy, and other nonlinear domains
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Heart rate variability
Measures of variability computed from the time, frequency, time-frequency, scale-invariant, entropy, and other nonlinear domains
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Heart rate variability
Measures of variability computed from the time, frequency, time-frequency, scale-invariant, entropy, and other nonlinear domains
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Thermal comfort scale
Thermal comfort assessed via a questionnaire using the ASHRAE 4-point scale ("1=comfortable to 4=very uncomfortable")
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Thermal comfort scale
Thermal comfort assessed via a questionnaire using the ASHRAE 4-point scale ("1=comfortable to 4=very uncomfortable")
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Thermal comfort scale
Thermal comfort assessed via a questionnaire using the ASHRAE 4-point scale ("1=comfortable to 4=very uncomfortable")
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Thermal sensation scale
Thermal sensation will be assessed using the ASHRAE 7-point scale ("0=neutral to 7=extremely hot")
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Thermal sensation scale
Thermal sensation will be assessed using the ASHRAE 7-point scale ("0=neutral to 7=extremely hot")
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Thermal sensation scale
Thermal sensation will be assessed using the ASHRAE 7-point scale ("0=neutral to 7=extremely hot")
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Thirst sensation scale
Thirst sensation will be quantified using a 9-point scale ("1=not thirsty at all to 9=very, very thirsty")
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Thirst sensation scale
Thirst sensation will be quantified using a 9-point scale ("1=not thirsty at all to 9=very, very thirsty")
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Thirst sensation scale
Thirst sensation will be quantified using a 9-point scale ("1=not thirsty at all to 9=very, very thirsty")
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Rating of perceived exertion
Rating of perceived exertion will be quantified using a 14-point scale ("6=no exertion at all to 20=maximal exertion")
Time frame: End of 30 minute exercise bout 1 (average of last 5 minutes).
Rating of perceived exertion
Rating of perceived exertion will be quantified using a 14-point scale ("6=no exertion at all to 20=maximal exertion")
Time frame: End of 30 minute exercise bout 2 (average of last 5 minutes).
Rating of perceived exertion
Rating of perceived exertion will be quantified using a 14-point scale ("6=no exertion at all to 20=maximal exertion")
Time frame: End of 30 minute exercise bout 3 (average of last 5 minutes).
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