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

University of Ottawa

Status: Completed

Conditions: Cold Exposure; Thermoregulation; Heat Stress; Exercise

Treatments: Other: Pre-Cooling; Other: No Cooling

Study type: Interventional

Funder types: Other

Identifiers

NCT06670339

HEPRU-2024-08-B

Details and patient eligibility

About

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.

Enrollment: 10 patients

Sex: Male

Ages: 18 to 30 years old

Volunteers: Accepts Healthy Volunteers

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

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Crossover Assignment

Masking: None (Open label)

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10 participants in 2 patient groups

No Cooling

Active Comparator group

Description:

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.

Treatment:

Other: No Cooling

Pre-Cooling

Experimental group

Description:

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).

Treatment:

Other: Pre-Cooling