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Lead Stories: Tuesday, December 2, 2008

Does your heart get tired when running and/or during other types of exercise?

Posted March 26th, 2007 at 9:59 AM by Hariz Siddiqui

Section: Health & Fitness, Exercise

healthy heartA healthy heart is so strong that it is almost never a cause of tiredness during exercise.

Tiredness during exercise comes from your muscles. They run out of fuel or out of oxygen. Skeletal muscles use both fat and sugar for energy.

When your muscles run out of their stored sugar supply, called glycogen, they cannot contract and function adequately. You feel tired, your muscles hurt and you have difficulty coordinating them.

On the other hand, your heart muscle gets energy directly from fat and sugar in your blood and even from a breakdown product of metabolism called lactic acid. It is virtually impossible for the heart muscle to run out of fuel unless you are starving to death.
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