.
When the body requires energy but the respiratory and circulation system can't provide enough oxygen the cells can perform respiration. In this case glucose is changed to and a smaller amount of energy is released.
Glucose ==> Latic Acid + Energy
The lactic acid causes stiffness and in muscles. To remove the lactic acid the body has taken in extra oxygen. This is known as the and is why people continue to breathe heavily immediately after exercise.
Latic Acid + Oxygen ==> Carbon dioxide + Water