Runners only have enough stored ATP in their muscle cells to run for about five seconds. Which answer correctly explains how the runner’s body adjust to the longer distance, for example, a marathon (42.1 km)?
A: The runner's body will convert stored fat molecules into energy.
B: The runner's body will create the needed energy by breaking down proteins.
C: The runner's body will supply the needed energy by producing starch.
D: The runner's body will produce the energy by activating the Golgi apparatus.

I think its either A or B

Our body produces mechanical energy when we run. This energy is actually transformed from the chemical energy contained in the energy substrates stored by the body and it is the ATP (adenosine triphosphate) which serves as an intermediate. The yield of this transformation depends on the type of activity; for running, the yield is about 25%, which means that our body uses only a quarter of the chemical energy to move forward, the rest is dissipated as heat.

An energetic substrate is a substance used by the body to produce energy. These substrates come from our diet and can be broken down into 3 main categories:

*carbohydrates

*lipids

*protein

These substrates differ in particular in the amount of energy they produce, the reserves stored by the body, the speed at which they are transformed.

Glycogen is the preferred fuel with fast paces or changes of pace. Glycogen alone can not cover the energy needs of a long race like a marathon.

Lipids are a good fuel from the point of view of energy efficiency (9kcal / g against 4kcal / g for carbohydrates) and also in terms of reserves stored in the body. On the other hand, they require oxygen and energy for their degradation. Their rate of degradation is therefore slower than that of carbohydrates: the energy is released more slowly.

During the effort, the proteins can represent up to 10% of the energy supply but only in case of lack of glucose, and for efforts of long durations (several hours) (that remains less than the lipids).