Although most wearable fitness-tracking devices do offer a wealth of features, the fact is that many of those features are based on the number of steps that the user has walked or run. According to a new study, inexpensive smartphone apps are just as good if not better at measuring that sort of data.

The study was conducted at the University of Pennsylvania, and involved having 14 test subjects walk on a treadmill. Each person did two 500-step walks and two 1,500-step walks, while wearing three fitness-tracking devices on their wrists and carrying two app-running smartphones in their pants pockets.

The devices were a Fitbit Flex, Jawbone UP24 and a Nike Fuelband. The phones were an iPhone 5s simultaneously running the Fitbit, HealthMate and Moves apps, and a Galaxy S4 running the Android version of Moves. Each participant also had a pedometer and two accelerometers attached to their waistband, plus an observer manually counted their steps using a tally counter.

After the walks were completed, the actual number of steps were compared to the number recorded by the devices and apps. While the relative difference in mean step count ranged from -6.7 to 6.2 percent for the apps, the devices were off by -22.7 to -1.5 percent.

Although step count is just one of many features on a typical wearable, the researchers point out that various other measures, such as distance traveled and calories burned, are typically derived from that data.

"In this study, we wanted to address one of the challenges with using wearable devices: they must be accurate. After all, if a device is going to be effective at monitoring — and potentially changing — behavior, individuals have to be able to trust the data," said lead study author Meredith A. Case, BA. "We found that smartphone apps are just as accurate as wearable devices for tracking physical activity."

A research letter on the study was published this week in the journal JAMA.