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Your pulse rate speeds up to pump extra food and oxygen to the muscles. Breathing speeds up to get more oxygen and to get rid of more carbon dioxide. When a fit person, such as an athlete, exercises the pulse rate, breathing rate and lactic acid levels rise much less than they do in an unfit person.
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Heart speeds up to pump extra food and o2 in muscles..breathing speeds up to get more o2 and give more co2..when a fit person exercises the heart pumps more n more blood so that's y the heart starts beating rapidly and forcefully, which increases the heartbeat.

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