How Fitbit Works

It's the brand new craze that's sweeping the nation--Fitbit! I'm sure most have, one way or another, come across these personal fitness trackers. Marketed as a way for the average consumer to keep a close watch on their daily activity, a Fitbit is a watch or wearable clip that monitors the steps you take, the calories you burn, and (depending on the version you own) your heart rate. Downloading the Fitbit app for your smartphone takes things a step further: If you sync the app with your Fitbit, you can scan the bar codes of your food and count the calories you consume, log in what you do when you go to the gym, and even challenge friends to walk more steps than you. More recently, Fitbit has come out with a sleep tracking feature.

Now, I know humanity's made some pretty decent technological progress in the few hundreds of thousands of years we've been ambling around this planet. We're in the Digital Age. We've put men on the moon, split the atom, and invented Hot Pockets. But for a long while, I was skeptical about Fitbits. How could a piece of plastic count how many calories I've burned? So I looked it up, and here's what I found.

To track steps, Fitbits use something called a three-dimensional accelerometer to track the user's movement as well as the intensity of that movement. It's quite similar to what's used in Wii remotes. This, simply, is how Fitbit tracks steps. However, this raw accelerometer data is pretty useless on its own. Fitbit relies on special algorithms to interpret it into something useful--the caloric and perambulatory information we so crave.

It seems that the engineers of Fitbit had to resort to plain old trial and error in order to finely tune the algorithm that the devices use. They compared Fitbit's algorithm to that of other, more established test machines in order to see how well it worked. For example, when the engineers were developing the feature assessing how many calories the user burns, they compared Fitbit's results with those of a portable telemetric gas analysis system. (The gas analysis system, which is so great an assessor of calorie use that googling it yields mostly scholarly articles I haven't got the time to peruse, analyzes gas composition as we exhale.) Fitbit then takes into account your basic metabolic rate (BMR), which includes heart rate and brain activity, and adds it to the data collected from the accelerometer to calculate the calories you burn.

Fitbit's sleep tracker is similar to its step tracker; it merely logs whether or not you're moving. So, if you're wearing your Fitbit while you're in bed but you can't fall out, the Fitbit will assume you're fast asleep. Well, I guess that's the thing about technology: There's always room for improvement.

Sources

• How FitBit Works--HowStuffWorks.com
• How does Fitbit estimate how many calories I've burned?--Help.Fitbit.com
• Fitbit image--Fitbit.com