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Lead Stories: Wednesday, December 3, 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

A 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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Exercise makes cells more efficient; increases overall health & life expectancy

Posted March 23rd, 2007 at 9:15 AM by Jeanie Rebb

Section: Health & Fitness, Exercise

Why does risk for heart attacks, strokes or diabetes increase with age? A team from Yale University showed that as you age, you lose your ability to make AMP-activated protein kinase (AMPK) (Cell Metabolism, February 2007). This enzyme functions to increase mitochondria in muscles.

Anything that reduces the number or efficiency of mitochondria interferes with your body’s ability to burn fat and sugar for energy. As a result, blood sugar, fat and cholesterol levels rise.
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