Cold Exposure, Exercise, Heat Stress, Thermoregulation
Conditions
Keywords
Cold Stress, Heat Stress, Heat Dissipation, Physical Activity, Performance, Athletes, Workers
Brief summary
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.
Interventions
OTHERNo Cooling
Participants will not be pre-cooled prior to completing a 60-minute moderate-intensity exercise bout in the heat.
OTHERPre-Cooling
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.
Sponsors
University of Ottawa
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
BASIC_SCIENCE
Masking
NONE
Eligibility
Sex/Gender
MALE
Age
18 Years to 30 Years
Healthy volunteers
Yes
Inclusion criteria
* Healthy young males (18-30 years) * Non-smoking * English or French speaking * Ability to provide informed consent
Exclusion criteria
* Presence of chronic diseases (e.g., hypertension, diabetes) * Acute illness (e.g., flu, COVID-19) * Physical restriction limiting physical activity * Use of medication judged by the patient or investigators to make participation in this study inadvisable. * Sedentary
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Rating of perceived exertion | Final 15 minutes of exercise | Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion) |
| Evaporative heat loss at end exercise | Final 15 minutes of the 60 minutes exercise bout | Evaporative heat loss as assessed using a direct air calorimeter |
| Dry heat loss at end exercise | Final 15 minutes of the 60 minutes exercise bout | Total dry heat loss as assessed using a direct air calorimeter |
| Total heal loss at end exercise | Final 15 minutes of the 60 minutes exercise bout | Net heat loss (dry plus/minus evaporative heat exchange) as assessed using a direct air calorimeter |
| Body heat storage during the 60-minute exercise bout | Over 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 |
| Core temperature at end of exercise | Final 15 minutes of exercise | Rectal temperature during final 15 minutes of exercise. Rectal temperature is measured continuously throughout the intervention. |
| Relative change in core temperature at end of exercise | Change over the 60-minute exercise bout | Change in rectal temperature from baseline resting. |
| Heart rate at end exercise | Final 15 minutes of exercise | Heart rate during final 15 minutes of exercise. Rectal temperature is measured continuously throughout the intervention. |
| Mean skin temperature at end of exercise | Final 15 minutes 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% |
| Relative change in skin temperature at end of exercise | Change over the 60-minute exercise bout | 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% |
| Thermal sensation A at end exercise | Final 15 minutes of exercise | Thermal sensation assessed via a self-report questionnaire upon verbal prompting (7-point scale; -3: cold to +3: hot) |
| Thermal sensation B at end exercise | Final 15 minutes of exercise | Thermal sensation assessed via a self-report questionnaire upon verbal prompting (7-point scale; 0: neutral to 7: extremely hot) |
| Thermal comfort at end exercise | Final 15 minutes of exercise | Thermal comfort assessed via a self-report questionnaire upon verbal prompting (4-point scale; 1: comfortable to 4: very uncomfortable) |
| Thirst sensation at end exercise | Final 15 minutes of 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) |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Heart rate variability at end of exercise | Final 15 minutes 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 |
Countries
Canada
Outcome results
None listed