How Exercise Affects Your Heart

Look around; about three-quarters of the people you see are either inactive and out of shape. But you run or work out regularly, and this makes many changes in your body because of a process called adaptation. When you work out, you stress your body, but not hard enough that you break it down. During the recovery period your body becomes stronger, so next time you can work out a little harder. This process can continue up to a limit, which varies for different people. In this series we shall look at the adaptation of your body, and see how it differs from most of the sedentary people you see each day.

Your heart is a muscle whose job is to pump blood. Exercise strengthens muscles and makes them larger. The left ventricle, a lower heart chamber, is especially likely to become larger, with thicker walls, in regular exercisers. This is so characteristic it is called "athlete's heart."

When your heart becomes stronger and larger it can push out more blood with each beat, so it doesn't have to work so hard. If your heart pumps about 70 milliliters of blood per beat, and your heart rate is 70 beats per minute, you pump 4,900 milliliters of blood in a minute. After exercising for a while your heart improves, and can pump maybe 80 milliliters with each beat. To pump the same 4,900 milliliters per minute, it need beat only about 61 times per minute. It is not unusual for aerobically fit recreational athletes to have resting pulse rates in the 50s, or even in the 40s.

There is a maximal value for your heart rate, a rate that it cannot exceed. You can measure your maximal heart rate by taking a treadmill maximal stress test. You run on a treadmill at gradually increasing pace and incline until you reach exhaustion. Your maximal heart rate doesn't change much after you've been exercising for a long time. It might increase slightly if you develop an ability to push yourself harder as you gain experience in high intensity workouts. Over time, your maximal heart rate decreases, although much more slowly than that of a sedentary person.

Avoid calculating your maximal heart rate from a formula, such as 220 minus your age. This can only give an average value, and this average is wrong for most age groups. Also there is a wide range of real values, as much as 30 beats above and below the average.

Some coaches teach competitive runners to judge workout intensity by their heart rates. In practice, you can do just as well by assessing how you feel: hard or easy. The biggest benefit of monitoring your heart rate probably is that it prevents you from working out too hard on easy days. If you enjoy gadgets, you might like to wear a heart rate monitor, but recreational athletes don't need one.

When you see the people around you, think about your powerful heart slowly and surely pumping blood all around your body, while two thirds of those folks may have hearts beating twice as fast to do the same job.

Volume 15, Number 7, Running & FitNews
?The American Running Association.

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