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Name: guardian
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993


Question:
How many units (liters/sec.) of oxygen do humans require to remain alive under:

1- relaxed conditions ?
2- and during heavy exertion, such as swimming?



Replies:
The amount of oxygen your cells require is the same whether you are watching TV or swimming a 500 Free. But you breathe faster while swimming because you need to repay the "oxygen debt" which accumulated during the exercise. Here is how it happens: Normally glucose is converted into pyruvate by glycolysis. Then in the mitochondria the pyruvate is oxidized completely to CO2 and H2O using oxygen and resulting in lots of energy in the form of ATP. At rest normal breathing delivers oxygen at just the right rate for these reactions to take place unnoticed by you. During extreme exercise the oxygen cannot be carried to the muscles fast enough to oxidize pyruvate to produce all the ATP needed just then. So the muscles use stored glucose in the form of glycogen to generate ATP. But glycogen cannot be oxidized in the same way as glucose; it must be fermented. This results in much less ATP (but still some) and lactic acid (not CO2 and H2O). All this lactic acid must be converted back into glucose in a set of reactions that require oxygen. (These reaction-called gluconeogenesis take place in the liver.) So while you are exercising and making lactic acid in your muscles, you are breathing heavily so your liver can convert lactic acid back to glucose. The excess oxygen consumed in the recovery period represents the repayment of the "oxygen debt" - the amount of oxygen required to supple ATP for gluconeogenesis in order to regenerate the glycogen used during the intense exercise.

Dr. Pam



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