Dear student, The food has stored energy, which is released during respiration. Therefore, all living organisms respire to get energy from food by breathing the air. During heavy exercise, fast running , cycling, walking for many hours or heavy weight lifting, the demand for energy is high. Also during running, due to lack of oxygen ,some muscles may respire anaerobically and form lactic acid . Therefore, to meet the extra demand of energy, an athlete breathes faster and deeper than usual after finishing the race .Regards.