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

NCT06670339 | Completed

• 1 other identifier: HEPRU-2024-08-B
• Study Type: interventional
• Target: 10
• Locations: 1 country
• Sites: 1

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.

Conditions

Thermoregulation; Cold Exposure; Heat Stress; Exercise

Keywords

Cold Stress; Heat Stress; Heat Dissipation; Physical Activity; Performance; Athletes; Workers

Outcome Measures

Primary Outcomes (14)

• Evaporative heat loss at end exercise

  Evaporative heat loss as assessed using a direct air calorimeter

  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

  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

  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

  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.

  Final 15 minutes of exercise

• Relative change in core temperature at end of exercise

  Change in rectal temperature from baseline resting.

  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.

  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%

  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%

  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)

  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)

  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)

  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)

  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)

  Final 15 minutes of exercise

Secondary Outcomes (1)

• Heart rate variability at end of exercise

  Final 15 minutes of exercise

Study Arms (2)

No Cooling

ACTIVE COMPARATOR

Participants will complete 60 min of continuous semi-recumbent cycling at a fixed metabolic heat load (200 W/m2) in the heat (wet-bulb globe temperature of 29°C; 37.5°C and 35% relative humidity) (Control condition) without pre-cooling.

Other: No Cooling

Pre-Cooling

EXPERIMENTAL

Participants will undergo a cold-water immersion (\~17°C) to elicit a decrease in rectal temperature by 0.5°C from baseline values. Thereafter, once the target temperature is achieved, participants will complete 60 min of continuous moderate-intensity cycling (200 W/m2) in the heat (wet-bulb globe temperature of 29°C; 37.5°C and 35% relative humidity).

Other: Pre-Cooling

Interventions

No Cooling OTHER

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

No Cooling

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.

Pre-Cooling

Eligibility Criteria

• Age: 18 Years - 30 Years
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• Healthy young males (18-30 years)
• Non-smoking
• English or French speaking
• Ability to provide informed consent

You may not qualify if:

• 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

Sponsors & Collaborators

• University of Ottawa: lead

Study Sites (1)

University of Ottawa

Ottawa, Ontario, K1N6N5, Canada

Location

MeSH Terms

Conditions

Heat Stress Disorders; Motor Activity

Condition Hierarchy (Ancestors)

Wounds and Injuries; Behavior

Study Officials

• Glen P Kenny, PhD

  University of Ottawa

  PRINCIPAL INVESTIGATOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Professor

Study Record Dates

• First Submitted: October 28, 2024
• First Posted: November 1, 2024
• Study Start: October 24, 2024
• Primary Completion: February 27, 2025
• Study Completion: February 27, 2025
• Last Updated: June 17, 2025

Record last verified: 2025-06

Data Sharing

• IPD Sharing: Will share
• Shared Documents: STUDY PROTOCOL, SAP, ANALYTIC CODE
• Time Frame: Following publication of the main study report(s)
• Access Criteria: Approved analysis plan and signed access agreement

Locations

CA (1)