Children Rehydration During Exercise

Subject will enter a warm room with a temperature between 28-30°C (80-85°F). Then, subjects will undergo a 3-hour walk, cycle, and rest protocol. The exercise intensity is based on 70% of the subject's predicted heart rate using the formula: 220 beats per minute (bpm) - 10 years of age = 210 bpm, and 70% equals 147 bpm). This is an intensity in which the subject has an elevated breathing frequency but can still talk. During the 3-h period subject will complete the following one-hour test three times:

• 10 min walking on the treadmill at 70% of predicted max heart rate (~147 bpm)
• 5 min rest
• 10 min cycling on the cycle ergometer at 70% of predicted max heart rate (~147 bpm)
• 35 min rest

During the 3-h period, subjects will have free access to fluids Body weight and urine samples will be collected during the experiement

Inclusion criteria

• Girls and boys age 8 to 10 years
• Willing to walk and cycle in a warm environment (80-85°F)
• Body weight ≤85th percentile for their age group

Exclusion criteria

• History of conditions known to alter body water balance (diabetes, renal disease, etc.)
• Drugs that (may) influence hydration status (including Selective serotonin reuptake inhibitor (SSRI), ADHD medication, diuretics and corticoids)
• Physical or mental disabilities that would prevent participation in moderate-intensity treadmill walking/jogging and cycling
• Previous diagnosis of heat stroke
• Body weight ≥86th percentile for their age group