Breathing and bleeding – the problems of being big and running fast

Abstract

The ability to use oxygen during exercise is determined by a combination of the muscle mitochondrial density, the relative proportion of total body mass consisting of locomotory muscle, the gas exchange surface area and the capacity for conduction of oxygen from the gas exchange surface to the muscle cells, i.e. the heart and circulation. Other factors include: the ability to ventilate the lungs to ensure that a high gradient is maintained between the alveolar oxygen tension and that in the pulmonary capillaries to facilitate diffusion; the capillary density within muscle, the size of the muscle cells and the blood oxygen carrying capacity, which is primarily determined by the total blood volume and haemoglobin concentration.In absolute terms, the fastest animal on land is the Cheetah, which can reach speeds of up to 120 kmh. However, the Cheetah is a “sprinter” and can only achieve these speeds for distances of around 200 metres (<10 seconds).