When I started running seriously in 2004, I tracked my miles using my 1989 Honda Accord. From behind the wheel, I would retrace my route, measuring the miles I had just run.
Now there are not only Fitbits (FIT) but also Apple Watches (AAPL) and a host of rivals like Under Armour’s UA Band (UA) in the $1.7-billion-and-growing market for fitness wearables. Roughly 16% of U.S. adults wear activity-tracking devices, according to the research firm NPD Group. That number is expected to jump to 19% by the end of this year as devices become ever lighter and more sophisticated, tracking sleep, heart rate, and workout intensity.
So recently I became curious about how the new crop of activity trackers might improve my performance. I am a fairly committed runner, logging about 15 miles a week using the Nike+ app (NKE). Would new gear better prepare me for an upcoming race?
For several weeks I tested Under Armour’s new $400 HealthBox, which includes an activity-tracking band, a heart rate strap, and a “smart” scale that records your weight and body-fat data and tracks them over time. I also ran in UA’s $150 smart shoes that come with a built-in sensor—allowing me to run without any hardware, if that’s what I would prefer.
The accompanying app, UA Record, uses data cruncher IBM Watson (IBM) to help serve as a digital coach, offering workout reminders and goals. “This is what differentiates UA Record from the rest of the fitness-tracking apps,” chief executive Kevin Plank told analysts recently. “We deliver direction to help you reach your personal goals.”
Executives say this sensor-adorned gear can mold dedicated, higher-performing athletes, making them more conscious of their diets and the intensity of workouts. Under Armour has bet heavily on this strategy, spending $710 million in the past three years to buy just three mobile apps, including MapMyFitness. Together they create a digital community of 170 million members that log billions of activities and meals and offer continual advice.
I discovered a few kinks with UA HealthBox. It is easy to set up, with the exception of the heart strap, which didn’t work on my first run. After downloading a software update and spitting on the sensors to awaken them, I got it to operate smoothly.
iphone: Alamy; graphics courtesy of Under Armour
The high-tech scale greeted me with a friendly voice: “Hi, John.” It then told me my weight and body fat. The UA app also gave me some alarming advice, telling me to shed 27 pounds off my 5-foot 11-inch frame. I weigh 177, putting me at the high end of “normal weight,” according to the body mass index. While weighing the suggested 150 is also “normal,” the last time I weighed that little I was 15 years old. IBM Watson, I learned, is a hard-driving coach.
Thankfully the app allowed for a more flexible goal, ranging from 150 to 168 pounds.
I mostly used the apps and scale to monitor my workouts and weight; inputting my sleep and nutrition data each day felt too time-consuming. But I could see how tracking those additional metrics could help me determine what’s ideal before a long run. Perhaps I think seven hours of sleep is enough, but the data would prove me wrong and say nine hours is better.
Daily alerts reminded me to open the app to reveal a new fitness tip or just move. (As I typed this story, I got an alert: “It has been 60 minutes since you last moved.” Time for a coffee run.) And like many fitness bands, after I reached a certain number of steps it tickled my wrist with a light celebratory buzz, which had a motivating effect.
Photograph by Lucas Visser for Fortune Magazine
So what’s the bottom line? The UA Record app did motivate me to run more—I went from 15 miles to 25 miles a week. I also lost four pounds.
NPD consumer electronics analyst Ben Arnold says the audience this market serves is narrow, mostly early tech adopters and technology-minded fitness buffs. Under Armour’s “connected fitness” division grew by 178% last year, to $53.4 million, and analysts estimate it could hit $200 million by 2018, a small fraction of the brand’s $4 billion in sales.
As these sensors move into more gear, including shirts, shoes, baseball bats, and swimming caps, experts expect fitness wearables to become widespread. Under Armour’s bet is that users like me will see value in tracking each stride. As for me, I’m a convert for now. But NPD Group estimates that 39% of fitness-tracker owners stop using their device after six months. So check back in with me in a few months to be sure.
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A version of this article appears in the June 15, 2016 issue of Fortune with the headline “Working Out Smarter.”