According to the BBC, aerobic respiration requires oxygen in order to release energy from glucose for cellular use. Carbon dioxide and water are waste products of aerobic respiration. This process occurs in organelles called mitochondria, which are the energy producing parts of the cell.
Furthermore, the BBC states that during exercise the process of cellular respiration is accelerated due to the body's need for more energy. As oxygen and glucose must be delivered to the cells more quickly, the heart rate and the rate of breathing increase to match the demands, subsequently increasing blood flow. Muscles and the liver store glucose in the form of glycogen.