Fit Tech: FitPal for iPhone

FitPal is an iOS app designed to help you figure out how hard you should exercise at any given moment. Using your iPhone's back camera and flash, it measures your heart rate in beats per minute, or BPM. Then, using the difference between your standing and seated heart rates, determines what your functional capacity is—basically, what your energy level is like—to help you get the most out of your workout. That could explain why some people like to exercise in the morning instead of after work, or vice versa.

FitPal has two types of tests: a functional capacity test, which takes about two minutes and measures how much energy you have to expend on exercising, and a heart rate test, which takes about ten seconds and measures your heart rate during your workout.

The functional capacity test is simple and quick, and FitPal walks you through it using spoken instructions. (You can also turn these instructions off, if you find them annoying after your first use.) You’re instructed to take a seat, then to gently place a finger over your iPhone's back camera. The first time you use FitPal, it may take a few (or ten) tries to figure out exactly how to press your finger over the camera, but you’ll get used to it after a few uses.

Once your finger is in place, just press the "Begin" button to start the test. For the first 30 seconds, the app uses your iPhone's flash to measure your seated heart rate. Once it has determined your heart rate, it instructs you to keep your finger over the camera and stand up. The app then spends about a minute-and-a-half determining your standing heart rate, and how long it takes for your standing heart rate to return to normal.

After about two minutes, the app will be able to tell you how much functional capacity you have. FitPal measures functional capacity as a percentage, but to make it easier to understand, you are given a level of exercise—very light, light, medium, hard, and very hard. FitPal also tells you your heart rate reserve—the difference between your maximum heart rate (determined by your age) and your resting heart rate—and gives you an optimal heart rate range for your workout.

After you take the functional capacity test, the app takes you to a workout screen, which features two arrows: one at the top of your optimal heart rate range, and one at the bottom. During your workout you can test your heart rate periodically by placing your finger on the camera for about ten seconds, and the app will tell you if you're within your optimal range or if you should adjust your workout Intensity. (Your optimal range should fall somewhere between those arrows.) Though FitPal’s functional capacity test is what sets the app apart from other fitness aids, it's perhaps not as helpful as the heart rate test, depending on how versed you are in exercise physiology.

The science behind FitPal

The science behind FitPal is actually pretty straightforward, once you get right down to it. The functional capacity test first determines your resting heart rate (seated), and then asks you to stand up. When you stand up, gravity pulls your blood away from your heart. This causes your blood pressure to drop and your heart to beat faster, albeit temporarily, to compensate for the loss. The app then measures your faster heart rate, and how long it takes for your heart rate and blood pressure to return to normal, once your body realizes you're not in trouble—you're just standing up.

Next, FitPal analyzes your recovery time to determine how ready your heart is for exercise at the moment. Your functional capacity will vary, since you have different energy levels at different times, and these levels can be affected by a variety of factors, including food, sleep, and general health.

As I noted earlier, the functional capacity test is the main feature of FitPal, but it's not the most useful feature if you are more of a casual exerciser. After all, it's one thing to know your functional capacity is 20 percent, and it's another thing to be able to modify your routine to appropriately match this level. However, FItPal can help you determine the best time to workout. Just perform the functional capacity test several times a day—once every hour or so—for a couple of days, and you'll be able to see when your energy levels peak. It sounds like a lot of work, but the idea here is that you'll be able to roughly plan you workout schedule around these levels.

FitPal is also useful as a heart rate monitor. In my tests, I used a Veridian blood pressure monitor and an Adidas heart rate monitor watch to verify whether the FitPal app is accurate—and it is. Over the course of several days, FitPal consistently came within five BPM of both the Veridian monitor and the Adidas watch, and was within three BPM of the traditional "check your pulse and count how many times your heart beats in a minute" method. So if you're just looking for a convenient heart rate monitor, FitPal is totally worth the $2.

The Bottom Line

Though I was initially skeptical of FitPal and its ability to measure my heart rate using an iPhone 4’s camera, I'm happy to report that it's surprisingly accurate. Whether you're a veteran workout-a-holic who is wary of overtraining, a newbie exerciser who wants to learn a little about the science, or just an average person who thinks having a heart rate monitor on your iPhone is cool, FitPal is worth a look.

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