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Completed

NCT Number: NCT06670339

Effect of Pre-cooling on Whole-body Heat Loss During Exercise-heat Stress

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.

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Key information

Conditions

Thermoregulation Behavior Cold Exposure Exercise Heat Stress Heat Stress Disorders Motor Activity Wounds and Injuries

Age range

18 year–30 year

Sex eligibility

Male

Study type

Interventional

Phase

Not applicable

Primary location

University of Ottawa

Ottawa, Ontario, K1N6N5, Canada

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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

Treatment and study plan

No Cooling

Other

Participants will not be pre-cooled prior to completing a 60-minute moderate-intensity exercise bout in the heat.

Pre-Cooling

Other

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.

Primary outcomes

  1. Evaporative heat loss at end exercise

    Time frame: Final 15 minutes of the 60 minutes exercise bout

    Evaporative heat loss as assessed using a direct air calorimeter

  2. Dry heat loss at end exercise

    Time frame: Final 15 minutes of the 60 minutes exercise bout

    Total dry heat loss as assessed using a direct air calorimeter

  3. Total heal loss at end exercise

    Time frame: 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

  4. Body heat storage during the 60-minute exercise bout

    Time frame: 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

  5. Core temperature at end of exercise

    Time frame: Final 15 minutes of exercise

    Rectal temperature during final 15 minutes of exercise. Rectal temperature is measured continuously throughout the intervention.

  6. Relative change in core temperature at end of exercise

    Time frame: Change over the 60-minute exercise bout

    Change in rectal temperature from baseline resting.

  7. Heart rate at end exercise

    Time frame: Final 15 minutes of exercise

    Heart rate during final 15 minutes of exercise. Rectal temperature is measured continuously throughout the intervention.

  8. Mean skin temperature at end of exercise

    Time frame: 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%

  9. Relative change in skin temperature at end of exercise

    Time frame: 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%

  10. Thermal sensation A at end exercise

    Time frame: Final 15 minutes of exercise

    Thermal sensation assessed via a self-report questionnaire upon verbal prompting (7-point scale; -3: cold to +3: hot)

  11. Thermal sensation B at end exercise

    Time frame: 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)

  12. Thermal comfort at end exercise

    Time frame: 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)

  13. Thirst sensation at end exercise

    Time frame: 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)

  14. Rating of perceived exertion

    Time frame: 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)

Secondary outcomes

  1. Heart rate variability at end of exercise

    Time frame: 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

Sponsors and collaborators

Lead sponsor

University of Ottawa

Other

Registry information

Official study title

Effect of Pre-cooling the Body on Whole-body Heat Exchange in Young Males During Exercise in the Heat

Important dates

Study start
2024
Primary completion
2025
Study completion
2025
First posted
Nov 1, 2024
Registry last updated
Jun 17, 2025

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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