Exercise Intensity for Heat Stress

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.