Bad news, folks. I have exceeded my maximum heart rate.

Surprisingly, I am still able to write this newsletter, but how much longer I can continue, who can say? My wearable devices do not produce that reading.

After last week’s adventures with RunKeeper, I thought I’d experiment with some other monitoring devices, hoping to gain deeper insight into my fitness.

To get an idea of what to try, I queried some of my fitness professional colleagues. You can see their responses here. Each device has its distinguishing points.  Some note how much you sweat, for example, or how bright the sun is.  But the most popular devices focus on some combination of five types of data:

• Where you are
• How much you move
• What time it is
• Your heart rate
• What other people have done

Using these numbers, other data that you punch in, and standard formulas, the devices can calculate a lot of statistics about you, such as your rate of speed, miles moved, and calories burned, and then you can compare stats with other people.

A free app like RunKeeper can make your smart phone can do most of these things, but it’s hard to wear your phone while swimming or sleeping. That’s one reason for making devices you can wear on your wrist, or some other body part.

The Armour39 Chest Band

Another reason is to track the speed at which your heart is beating: your heart rate, also known as your pulse. Measuring it requires touching your skin. Heart monitors you wear on your wrist are notoriously inaccurate because they use optical technology. By contrast, chest bands can measure the actual electrical activity of your heart.

So for the past week I’ve been experimenting with the Armour39, a chest monitor from Under Armour. Why did I choose it? The company gave me one for free because I signed up as a blogger at IDEA, a convention for personal trainers.

The Armour39 seems accurate. At least it produces the same result that I do when I measure my pulse  the old-fashioned way, by pressing fingers against my wrist while sitting still.

But I don’t know what to do with the results it gives me.

In theory, measuring my heart rate should give me an idea how hard I’m working out.  If I don’t exercise hard enough, I won’t improve my fitness; if I exercise too hard, I might hurt myself.
The American Heart Association recommends exercising at 50 to 80 percent of your maximum heart rate. The American College of Sports Medicine argues that super athletes might have to go above that range to achieve results, while couch potatoes might be better off a bit below.

How Big is Your Heart?

There are formulas for estimating your maximum heart rate based on your age, but heart rates in healthy people vary so much that the formulas don’t tell you much. One reason is that your heart gets bigger as you do more aerobic exercise, so it doesn’t need to pump as fast to circulate the same amount of blood. But the change happens differently in different people — and isn’t even consistent among people the same age, doing the same sport.

The Armour39 includes a program for measuring your maximum heart rate. It coaches you to gradually increase your pace while running on a track or treadmill until you are sprinting all out.

When I took the assessment, I got a maximum rate of 153. According to the most common formula used for estimating maximum heart rates, this means I have the average heart rate of a 69-year-old. I’m 52.

After the assessment, I went for a run. I tried to beat the best time I had clocked with RunKeeper on my usual route in the Oakland hills, and succeeded: I increased my speed 5 percent, to 9:43 minutes per mile from 10:13.

I think warming up first (by doing the assessment) helped. But the Armour39 also reported that my maximum heart rate on the run reached 163, exceeding my maximal heart rate by 7 percent.

I felt fine afterwards. That leads me to one of three conclusions. Either the monitor didn’t work properly, I didn’t push myself hard enough in the assessment or I have a really big heart.

I like the third option.

Heart rate monitors might be able to tell you something else that is more useful: some research shows that if your heart rate falls less than 12 beats within a minute after you stop exercising, you might be at risk of heart disease. I’m OK, there. How about you?