Nutrition Science and Everyday Application - beta v 0.1

Fuel Sources for Exercise
The human body uses carbohydrate, fat, and protein in food and from body stores for
energy to fuel physical activity. These essential nutrients are needed regardless of the
intensity of the activity you are doing. If you are lying down and reading a book or running
a marathon, these macronutrients are always needed in the body. However, in order for
these nutrients to be used as fuel for the body, their energy must be transferred into the
high energy molecule known as adenosine triphosphate (ATP). ATP is the body’s immediate
fuel source and can be generated either with aerobic metabolism in the presence of oxygen
or anaerobic metabolism without the presence of oxygen. The type of metabolism that is
predominately used during physical activity is determined by the availability of oxygen and
how much carbohydrate, fat, and protein are used.
ANAEROBIC AND AEROBIC METABOLISM
Anaerobic metabolism occurs in the cytosol of the muscle cells. As seen in Figure 10.1., a
small amount of ATP is produced in the cytosol without the presence of oxygen. Anaerobic
metabolism uses glucose as its only source of fuel and produces pyruvate and lactic acid.
Pyruvate can then be used as fuel for aerobic metabolism. Aerobic metabolism takes place
in mitochondria of the cell and is able to use carbohydrates, protein, or fat as fuel
sources. Aerobic metabolism is a much slower process than anaerobic metabolism, but it
can produce much more ATP and is the process by which the majority of the ATP in the body
is generated.
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