What is the main function of the oxygen taken in through breathing?

to pump blood or circulate around the body

respiratory system

Explanation:

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the more fit you are, the faster the recovery. your heart rate drops most sharply in the first minute after you stop exercising; it should then fall about 20 beats a minute—a drop of less than 12 beats a minute is considered abnormal. this “recovery heart rate” is measured as part of an exercise stress test.