how do you demonstrate that oxygen is used up during aerobic respiration

Aerobic respiration occurs in the cytoplasm and mitochondria in the presence of oxygen. It always releases Carbon dioxide and water as an end product. Aerobic respiration utilizes oxygen present in the cells. For example, If a person is performing strenuous physical activities, then the oxygen in the cells gets used up at a much faster rate, thereby, causing oxygen deficiency in the cells because almost entire oxygen was utilized.