Several months ago, I tried out one of these devices, the Fitbit Ultra, which tracks not only the wearer’s number of steps but can also be used to monitor sleep (although that is not the device’s strong suit). The manufacturer says that users of the device increase the number of steps they take daily by 43% and ultimately lose an average of 13 pounds. Those numbers sound high, but the device does a good job at living up to expectations based on the cumulative Amazon reviews for the device: at present, the Fitbit Ultra has a near five-star average based on more than 1300 reviews on the site. When testing the device, I also could see how these devices can be effective. When using the Fitbit, I found myself oddly compelled to be more active than usual.
More recently, I had the opportunity to check out a similar product: the BodyMedia Fit Link. In every respect, this is a more serious device than the Fitbit. It is larger, more expensive, and more powerful in a number of ways. The device is registered by FDA as a Class II medical device. The manufacturer states that the device has been shown in a randomized controlled study to significantly improve weight loss when paired with a group weight loss program. While the device can be used to track activity levels,
The device is much more accurate than the Fitbit at estimating the number of calories your body burns—it measures your skin temperature, heat flux, and galvanic skin response. The accuracy of the BodyMedia Fit Link improves over time as its algorithm adapts to the workings of your body. The device can also draw on these measurements, in addition to gauging your activity level using a three-axis accelerometer, to determine when you are asleep. The manufacturer notes that the device captures more than 5000 data points per minute via four sensors. The Fit's ability to track sleep can help give you an idea of how your sleep cycle affects how you feel in your daily life and how well you perform in athletic activities.
Users can also use the system to track workouts and diet and to determine if they are gaining weight in near real time (has there been a caloric surplus so far today?) or if they are losing weight (has there been a caloric deficit?).
The level of functionality packed into this device is impressive. The surpasses the Fitbit in nearly every way except for two important categories: user-friendliness and size. I had the Fitbit up and running in substantially less time and, once it is up and running, it is a breeze to check how active you have been—albeit with less accuracy than the BodyMedia Fit Link. I wished though the device had a built-in display. Users must view data on their Bluetooth-paired smartphone or on their computer. It would also be nice if it were easier to enter foods into the system, as the current food database is somewhat limited in size.
As for size, the BodyMedia Fit measures 2.2 x 2.4 x 0.5 inches. (The company also makes a smaller armband, the CORE that also has a scaled down feature set.) The Fitbit, on the other hand measures 2 x 0.5 x 0.4 inches, and is clipped onto clothing or kept in a pocket; it is so small that it was easy to forget for long stretches of time that I was even wearing it. By contrast, the BodyMedia device is right up against the skin in the same spot for nearly all day (the manufacturer suggests taking it off for one hour each day). Although I wouldn’t say it is uncomfortable to wear, I was often prone to realize it was strapped to my arm. It is small enough as to not be nearly invisible beneath a shirt sleeve. Still, I wish it were smaller. It would be nice if, a few years down the line, Bodymedia could come out with a conformal electronics-based version of the technology.
Another consideration is battery life. When using it when Bluetooth, I had to charge the BodyMedia Fit Link once every three or four days or so. The Fitbit, on the other hand, can last about a week or so on a single charge.
To sum up, the BodyMedia device is more of a niche device than the Fitbit. While it is likely a better fit for serious users who want greater accuracy than devices like Fitbit Ultra can provide, it also demands more from the user. It's worth noting that the device seems to be designed primarily for individuals who want to lose weight, although it can also be used to track activity levels.
Brian Buntz is the editor-at-large at UBM Canon's medical group. Follow him on Twitter at @brian_buntz.