Exercise Intensity and Heat Responses in Children and Youth

Effects of Exercise Intensity on Thermoregulation in the Heat in Children and Youth

Little is known about how children and youth regulate body temperature during exercise in the heat compared with young adults, including whether differences in whole-body heat exchange contribute to their responses. The goal of this clinical trial is to determine how exercise intensity affects thermoregulation in boys and girls aged 9-16 years compared with young adult men and women aged 20-25 years. Participants will complete three study visits in a hot environment of 36°C (degree Celcius (97°F, degree Farenheit)), performing light-, moderate-, and vigorous-intensity exercise corresponding to metabolic heat production of 120, 160, and 200 W/m² (w=watts, m=meter), respectively. During each visit, participants will complete four 15-minute bouts of exercise (i.e., bout 1, 2, 3 and 4 respectively) separated by 15-minute rest periods. Testing will be performed in a whole-body air calorimeter, a specialized chamber that precisely measures heat lost through evaporation and dry heat exchange and the amount of heat stored in the body. These measurements, together with core temperature and heart rate, will allow researchers to determine how increasing exercise intensity affects the body's ability to lose heat and whether these responses differ between children and youth and young adults.

Inclusion Criteria:

• Healthy male or female.
• Aged 9-16 years or 20-25 years.
• Habitually active, defined as participating in regular physical activity at least 3 times per week for at least 20 minutes per session over the previous 6 months.
• Able to understand and communicate in English or French.
• For participants younger than 18 years, written parental or guardian consent and participant assent are required.

Exclusion Criteria:

• Acute illness at the time of testing (e.g., cold, flu, or infection).
• History of a chronic medical condition that may affect thermoregulation, cardiovascular function, or exercise capacity (e.g., cardiovascular disease, metabolic disorders, respiratory disease including asthma requiring regular medication, or neurological disorders).
• Use of medications known to affect thermoregulation, hydration status, or cardiovascular responses.
• History of heat-related illness (e.g., heat exhaustion or heat stroke).
• Digestive abnormalities or gastrointestinal conditions that may contraindicate ingestion of a telemetry pill.
• Any condition that, in the opinion of the investigators, would compromise participant safety or the integrity of the data.