One small thing that was mentioned in the book is that athletes in extremely good shape are able to control the amount of oxygen they take in. They trail their respiratory systems to take in oxygen at higher rates than mosts. But, even they can reach a point where the oxygen intake is not enough for their metabolic needs. This can be because the heart is unable to pump an adequate amount of blood at a rate fast enough to deliver oxygen to the muscles. Because of this, metabolism occurs without oxygen, anaerobic metabolism. This kind of metabolism i not as efficient as normal metabolism in converting food into energy. Anaerobic metabolism can cause waste products from the metabolism process to accumulate in the bloodstream. The waste products
