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

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

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 Overview

• Status: Completed
• Conditions: Exercise; Heat Stress; Thermoregulation; Cold Exposure
• Intervention / Treatment: Other: No Cooling; Other: Pre-Cooling

• Study Type: Interventional
• Enrollment (Actual): 10
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Canada
  • Ontario
    • Ottawa, Ontario, Canada, K1N6N5
      • University of Ottawa

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: No Cooling; 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; Participants will not be pre-cooled prior to completing a 60-minute moderate-intensity exercise bout in the heat.
Experimental: Pre-Cooling; 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; 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.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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 Outcome Measures

Outcome Measure	Measure Description	Time Frame
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	Final 15 minutes of exercise

Collaborators and Investigators

• Sponsor: University of Ottawa
• Investigators: Principal Investigator: Glen P Kenny, PhD, University of Ottawa

Study record dates

Study Major Dates

• Study Start (Actual): October 24, 2024
• Primary Completion (Actual): February 27, 2025
• Study Completion (Actual): February 27, 2025

Study Registration Dates

• First Submitted: October 28, 2024
• First Submitted That Met QC Criteria: October 30, 2024
• First Posted (Actual): November 1, 2024

Study Record Updates

• Last Update Posted (Actual): June 17, 2025
• Last Update Submitted That Met QC Criteria: June 13, 2025
• Last Verified: June 1, 2025

More Information

Terms related to this study

• Keywords: Physical Activity; Performance; Athletes; Workers; Heat Stress; Cold Stress; Heat Dissipation
• Additional Relevant MeSH Terms: Wounds and Injuries; Heat Stress Disorders
• Other Study ID Numbers: HEPRU-2024-08-B

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Deidentified participant data will be made available with approved analysis plan and signed access agreement
• IPD Sharing Time Frame: Following publication of the main study report(s)
• IPD Sharing Access Criteria: Approved analysis plan and signed access agreement
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP; ANALYTIC_CODE

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No