Why do we breathe more rapidly during exercise?

When we exercise,our muscles need energy,so,they use a chemical called adenosine triphosphate (ATP) for their energy source. During the process of "burning" ATP, your muscles need three things:

• They need oxygen, because chemical reactions require ATP and oxygen is consumed to produce ATP.
• They need to eliminate metabolic wastes (carbon dioxide, lactic acid) that the chemical reactions generate.
• They need to get rid of heat. Just like an electric motor, a working muscle generates heat that it needs to get rid of.

So,we need to take more oxygen in,& let carbon dioxide out.so,we breathe quicker.