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Maximum heart rate: Is it harmful to exceed it during exercise?

Posted Oct 01 2008 8:12pm

Some people enjoy using a heart rate monitor and find that it helps to motivate them, but you don’t need one. You can tell how fast your heart is beating just by paying attention to how you breathe. The only heart rate that you need to know is the training heart rate that makes your heart stronger. To strengthen your heart, you have to exercise vigorously enough to increase your heart rate at least 20 beats a minute beyond your resting heart rate.

You can tell when your heart rate is high enough to strengthen your heart because your body will require more oxygen than it does at rest, and you will start to breathe deeply and more rapidly. You should still feel comfortable and be able to talk. If you exercise so slowly that you never breathe more deeply or rapidly than your resting rate, you are not strengthening your heart. However, you don’t have to exercise at your maximum heart rate to become fit.

When you have been exercising for several months and your exercise program feels easy, you can decide whether you want to improve. If you would like to compete or just want to increase your level of fitness, a heart rate monitor can help you plan your training sessions, set goals, and measure your progress.

Instructions that accompany most heart rate monitors are based on a mythical maximim heart rate formula that predicts the fastest your heart can beat and still pump blood through your body. Although this formula is the gold standard used today, it is not based on science. In 1970, Sam Fox was the director of the United States Public Health Service Program to Prevent Heart Disease, and one of the most respected heart specialists in the world. He and a young researcher named William Haskell were flying to a meeting. They put together several studies comparing maximum heart rate and age. Sam Fox took out a pencil and plotted a graph of age verses maximum heart rate and said it looks like maximum heart rate is equal to 220 minus a person's age. For the last 30 years, this formula has been taught in physical education and heart function course and has been used to test heart function and athletic fitness.

The formula is wrong because your legs drive your heart; your heart does not drive your legs. Maximum heart rate depends on the strength of your legs, not the strength of your heart. When you contract your leg muscles, they squeeze against the blood vessels near them to pump blood from your leg veins toward your heart. When your leg muscle relax, your leg veins fill with blood. So your leg muscles pump increased amounts of blood toward your heart. This increased blood fills the heart and causes your heart to be faster and with more force. This is called the Bainbridge reflex that doctors are taught in their first year of medical school. The stronger your legs are, the more blood they can pump, which causes your heart to beat faster.

A pencil mark plotted on a graph during an airplane flight more than 30 years ago has been the accepted formula for maximum heart rate for more than 30 years and the fitness community has accepted this dogma for more than 30 years.

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