Differences in Nutrient Use During Exercise Between Children of Varying Body Mass Indices and Fitness Levels

We will examine fatty acid oxidation (FAO) and carbohydrate (CHO) oxidation at rest and during exercise in children of all body types and activity levels.

Children 8-11 years old who have done the "MI Energy" study will participate. Up to 80 children will be recruited to participate in this study at Arkansas Children's Nutrition Center (ACNC).

They will be asked to attend three study visits (baseline, and two exercise visits). For the exercise visits, they will follow a diet plan and be encouraged to avoid certain foods and activities.

Children will do two testing days with the following measures:

• Urine (pee) will be collected
• Body weight and height
• Exercise test on the bike - children will ride a stationary bike at a set intensity and at an intensity relative to their previous bike test during the study "MI Energy". The order in which they bike will be random. Before and during biking, children will wear a mask that will measure the gases in their breath and a monitor that will measure heart rate.

Inclusion criteria

• Boys or girls
• Ages 8-11 years
• All races
• All ethnicities
• All BMIs
• Children who completed a dual-energy x-ray absorptiometry (DXA) scan during "MI Energy" (IRB Protocol: 260376)
• Children who completed a fitness test during "MI Energy" (IRB Protocol: 260376) and achieved peak oxygen uptake (VO2 peak)
• All fitness levels [VO2 peak already determined under "MI Energy" (IRB Protocol: 260376)]
• Children whose parents consented to the following in the "MI Energy" (IRB Protocol: 260376) study:

A) be contacted about future follow-up studies to "MI Energy", and having the data that is collected about their child in "MI Energy" being used also in these follow-up studies; and B) information collected in the "MI Energy" study may be used in future research related to bioenergetics (for example, blood cell mitochondria function), nutrition, obesity, cardiovascular health, or development; and C) any biological samples collected in the "MI Energy" study may be used in future research related to bioenergetics (for example, blood cell mitochondria function), nutrition, obesity, cardiovascular health, or development.

Exclusion criteria

• Participants who have been excluded from participation in the study "MI Energy" (IRB Protocol: 260376).
• Participants whose parents report any change in medical history that may potentially affect participation and/or study outcomes as determined by PI.
• Participants whose parents report food allergies or intolerances to nuts, wheat, dairy, or eggs.
• Participants whose parents report unwillingness to follow dietary standardization.