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Heart Rate Monitors

By David Mendosa

Last Update: November 19, 2003

We can't let exercise get boring. It's so important to controlling your diabetes that we have to seek out new ways to keep our interest high.

I think it's easiest to be excited about what I'm doing when I'm walking on a trail. There's always something new, even if I have been down that path hundreds of times before.

60-70% of your maximum should be your goal

But even if you are working out at home on a treadmill, an exercise bike, or a StairMaster, you can make the time pass quicker by listening to music or motivational tapes. Alternatively, just using that time to clear your mind can also be rewarding.

Now, we also have gadgets that can help making our daily workouts more interesting. Some people use pedometers to measure how far they walk, but I've never been able to set one up accurately for my stride.

Much more valuable in my opinion are machines that measure how fast your heart is beating. They tell you both the degree of physiological adaptation and intensity of your effort.

That's what an electrocardiogram (ECG) does, but these machines are a bit too expensive, bulky, and complex for use while exercising. Photo-reflectance units such as ear clips or finger tip pulse monitors aren't reliable enough. I tested a friend's pulse monitor and found it to vary wildly from minute to minute.

A professor of electronics at Oulu University in Finland named Seppo Säynäjäkangas made what was essentially the first portable ECG machine. His company, http://www. Polar Electro Oy, in 1982 patented the first portable heart rate monitor.

By 1990 Polar was distributing a full line of inexpensive models worldwide and still dominates this market. Today Polar and at least five other manufacturers produce more than 50 different models. Prices start at $50, making them accessible even to recreational athletes.

With each beat, the heart generates electrical signals that can be measured on the skin. A heart rate monitor transmitter contains two electrodes that detect these signals. The electrodes are mounted on a sealed transmitter attached to the chest with an elastic belt. The transmitter detects the voltage differential on the skin during every heartbeat and wirelessly relays the signal to a wrist receiver—which looks just like a wristwatch. The receiver displays your heart rate in beats per minute.

When you use a heart rate monitor, the first step is to calculate your maximum heart rate—the fastest that your heart can beat for one minute. The safest way is to have your doctor give you a stress test, but that can cost several hundred dollars. If you are 35 or older, have lived a sedentary life, or are in poor physical condition, you should at least have a thorough physical exam before starting an exercise program.

You can, however, determine your maximum heart rate without stressing it. The age-adjusted formula is the most common one. For women the formula is 225 minus your age in years. For men it is 220 minus your age in years.

A newer formula, based on both age and body weight, might be slightly more accurate. You can find it in my favorite book on the subject, The Heart Rate Monitor Book, by Sally Edwards, a competitive runner.

Next, pick the training zone or heart rate range you are shooting for. While the zones are arbitrary divisions and differ from one expert to another, what Ms. Edwards recommends makes a lot of sense.

For most of us with diabetes who are exercising to strengthen our heart and control our blood glucose, Zone 3, which is 60 to 70 percent of your maximum heart rate should be your usual goal.

This aerobic zone "benefits not only your heart, but also you respiratory or breathing system [which] increases your endurance."

If you keep your heart rate in this zone for at least 30 minutes every other day, you're doing great. At too high of a heart rate your effort can be counterproductive, while too low of a rate won't help enough.

Keeping track of how you are doing with your heart rate monitor can keep your life interesting even when you are working out. And that means healthier. 

The American Diabetes Association originally published this article on its Web site as one of my “About the Internet” columns.

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