When we have run a long distance, we feel tired. We have to stop. Why

1.	When we have run a long distance, we feel tired. We have to stop. Why is that?
Answer» We need energy to run. Hence when we run a long distance, the food present in the body is continuously burn to release energy. This energy is used to do the work of running. After running a long distance the food gets exhausted and the energy released decreases and therefore we feel tired and we stop.

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