The level of carbon dioxide in the blood controls the pH (acid/alkali) balance. Carbon dioxide converts to carbonic acid to prevent respiratory alkalosis. If there is insufficient carbonic acid then cells produce lactic acid, which makes your muscles tired and sore, preventing athletes from training hard and giving top performance.

Haemoglobin carries oxygen to the muscles and tissues. When there are adequate levels of carbon dioxide, haemoglobin releases the oxygen more readily, this increases the amount of oxygen able to be used by the muscles while you exercise.

Breathing too much increases the amount of mucus being produced in the airways, which reduces the space inside them. The smooth muscle wrapped around these tubes tightens and when these two things combine they restrict airflow.