Endurance exercise performance declines in hot environments as core body temperature increases. To enhance performance, body pre-cooling strategies, such as cold-water immersion have been employed to lower resting core temperature thereby increasing the body's heat storage capacity. In turn, the increase in body core temperature associated with exercise in the heat is blunted, allowing the individual to exercise at higher intensity and or for a longer period of time. However, the mechanisms by which pre-cooling impacts heat exchange during exercise remain unclear. While existing research has focused on the performance benefits of pre-cooling the body, relatively little is known about the impacts of pre-cooling on whole-body heat exchange during an exercise-heat stress. Investigators will therefore evaluate whole-body heat exchange (dry ± evaporative heat loss as assessed using a direct air calorimeter) during a prolonged (1-hour) moderate-intensity cycling bout in the heat (wet-bulb globe temperature of 29°C; equivalent to 37.5°C, 35% relative humidity) performed with and without pre-cooling by cool-water (\~17°C) immersion.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
10
Participants will not be pre-cooled prior to completing a 60-minute moderate-intensity exercise bout in the heat.
Participants will be immersed in cold (\~17°C) water to elicit a decrease in rectal temperature by 0.5°C from baseline values prior to completing a 60-min moderate-intensity exercise bout in the heat.
University of Ottawa
Ottawa, Ontario, Canada
Evaporative heat loss at end exercise
Evaporative heat loss as assessed using a direct air calorimeter
Time frame: Final 15 minutes of the 60 minutes exercise bout
Dry heat loss at end exercise
Total dry heat loss as assessed using a direct air calorimeter
Time frame: Final 15 minutes of the 60 minutes exercise bout
Total heal loss at end exercise
Net heat loss (dry plus/minus evaporative heat exchange) as assessed using a direct air calorimeter
Time frame: Final 15 minutes of the 60 minutes exercise bout
Body heat storage during the 60-minute exercise bout
Change in body heat storage (i.e., amount of heat stored in the body) calculated as the temporal summation of metabolic heat production and total heat loss
Time frame: Over the 60 minute exercise bout
Core temperature at end of exercise
Rectal temperature during final 15 minutes of exercise. Rectal temperature is measured continuously throughout the intervention.
Time frame: Final 15 minutes of exercise
Relative change in core temperature at end of exercise
Change in rectal temperature from baseline resting.
Time frame: Change over the 60-minute exercise bout
Heart rate at end exercise
Heart rate during final 15 minutes of exercise. Rectal temperature is measured continuously throughout the intervention.
Time frame: Final 15 minutes of exercise
Mean skin temperature at end of exercise
Skin temperature measured continuously 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: Final 15 minutes of exercise
Relative change in skin temperature at end of exercise
Change in skin temperature from baseline resting as assessed at 4-sites (chest, upper arm, thigh, calf) with mean value calculated as weighted value of 4 sites - uper arm, 30%; chest, 30%; thigh, 20%; and calf, 20%
Time frame: Change over the 60-minute exercise bout
Thermal sensation A at end exercise
Thermal sensation assessed via a self-report questionnaire upon verbal prompting (7-point scale; -3: cold to +3: hot)
Time frame: Final 15 minutes of exercise
Thermal sensation B at end exercise
Thermal sensation assessed via a self-report questionnaire upon verbal prompting (7-point scale; 0: neutral to 7: extremely hot)
Time frame: Final 15 minutes of exercise
Thermal comfort at end exercise
Thermal comfort assessed via a self-report questionnaire upon verbal prompting (4-point scale; 1: comfortable to 4: very uncomfortable)
Time frame: Final 15 minutes of exercise
Thirst sensation at end exercise
Thirst sensation assessed via a self-report questionnaire upon verbal prompting (9-point scale; 1: not thirsty at all to 9: very, very thirsty)
Time frame: Final 15 minutes of exercise
Rating of perceived exertion
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion)
Time frame: Final 15 minutes of exercise
Heart rate variability at end of exercise
Measures of variability computed from the time, frequency, time-frequency, scale-invariant, entropy, and other nonlinear domains (R-R interval data extracted from the electrocardiogram). Measured continuously using a holter monitor with Zymed placement
Time frame: Final 15 minutes of exercise
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