why do we breathe fast after running?

After finishing the race we need extra energy. we breath faster and deeper to supply more oxygen to our body cells, it speeds up the break down of the food and more energy is realesed. 

because lungs inhales and exhales more oxygen and gives out carbon dioxide really very fast and thus we need more oxygen and we breathe fast.

Because our body muscles need energy and to fulfil the demand for oxygen to get energy , we breathe fast

because while running our body uses all energy and to aquire more energy ,we need oxygen so we breathe fast

it is so because when we run , we need extra energy and anaerobic respiration takes place to fulfill the demand of energy.

this is because the requirement of energy increases which causes aerobic respiration to level up at a higher rate , this builds up the amount of carbon dioxide and when compared oxygen is lesser . the body  experiences breathlessness when trying to compensate for the higher demand of oxygen .