|MadSci Network: Medicine|
The amount of air breathed in and out varies from about 6 litres/minute at rest (in an average adult) to about 50 litres/minute after hard exercise. The amount of oxygen absorbed varies from about 300 ml/min at rest to 3500 ml/min for the average male adult during heavy exercise, and up to 6000 ml/min in athletes. Curiously the main difference fitness makes is in the amount of blood pumped around the body during exertion. The fitter you are, the more effectively the heart pumps, i.e. more blood is pumped with each heartbeat hence more oxygen is transported with each beat. Both unfit and fit people breathe about the same amount of air in and out during heavy exercise, and will have about the same maximal heart rate. The main difference is in the amount of blood being pumped through the lungs (greater in a fitter person for the same heart rate), and thus the amount of oxygen being transported. Therefore a fit person, who has the ability to transport more oxygen in his or her blood (and hence to the muscles) during exercise will be able to achieve greater levels of exertion than an unfit person. Dr C-P
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