Armour39: A Fitness Tracker That’s Smarter Than Most

ReadWriteBody is an ongoing series where ReadWrite covers networked fitness and the quantified self.

I’ve long been fascinated by Armour39, an activity-tracking device made by Under Armour. I got a chance to test it in March at the South By Southwest Interactive conference in Austin, Texas. Since then, I’ve continued to work out with the device in San Francisco. it’s been pushing me to the edge, in a good way—and I’ve been putting the device through some torture tests of my own.

My takeaway: Armour39 is not for the everyday gym rat or trail junkie. But for someone like me, who is interested in testing and improving my fitness through activities like Olympic weightlifting, high-intensity interval training, Tabata, and Bikram yoga, it may be the perfect device. Eventually.

My testing of Armour39 also enlightened me on how Bluetooth works in fitness devices, and how the intentional quirks of the device actually make it superior for some kinds of workouts.


Under Armour trainer Nate Costa helps ReadWrite editor-in-chief Owen Thomas put on the Armour39 activity tracker.

Strap It On And Work Your Heart Out

The Armour39 device is a chest strap that’s bulkier than comparable devices, with a rubbery chest plate that looks almost like a boxing championship belt.

If you’re bothered by standard chest straps, the Armour39 is not for you. The strap also contains heart-rate sensors, and it holds a module that contains the brains of the device—a Bluetooth radio, processors for the heart-rate signal, and an accelerometer to detect motion. The module also has enough storage to capture data, a crucial difference from most devices that simply relay heart-rate data to your phone.

The Armour39 module also has lights that indicate its status, which is a significant improvement over other devices that leave you guessing over whether they’re ready to pair with your phone or just running low on battery. These light up when you click it into the plate. Then, when you launch the app, it’ll indicate that it’s connecting to the module. And if all goes well—more on that in a bit—you’re ready to work out.


The Armour39 app displays your heart-rate and workout intensity in real time.

Under Armour has developed its own scoring mechanism for workouts called “Willpower.” It goes from a scale of 0 to 10. Mark Oleson, Under Armour’s director of research and innovation, says that Willpower is “exponential” rather than linear, which means you’ll have to continually up your game to go from a 3 to a 4 to a 5.

The highest score I got was an 8.9, which was achieved during a particularly vicious workout that involved timed clean-squat-presses, with minimal rest between sets. My heart rate rarely fell below 150 bpm throughout these maneuvers, which is the kind of effort Armour39 is looking for when it calculates Willpower. On other workouts where I took more rest breaks, I struggled to break a Willpower of 4.

If you typically do a circuit of weight machines at the gym, you won’t be happy with your Willpower scores. Armour39’s target market is serious athletes that compete in sports or are into exercise styles like CrossFit. If you’re simply trying to stay in an elevated heart-rate zone, standard heart-rate devices from the likes of Polar or Pear Sports will do just fine.


At the end of a workout the Armour39 app shows you your average heart rate, calories burned, and other workout statistics.

In November 2013, Under Armour acquired MapMyFitness, a maker of apps that collectively track your runs and workouts. Already, MapMyFitness has been collaborating with its new parent, specifically around integrating Armour39 with its family of apps. The company gave me early access of beta versions of the MapMyFitness and MapMyRun apps so I could test how Under Armour’s hardware worked with its new software arm. I also tested Armour39 with its original app developed by Under Armour.

My main complaint with Armour39 is the app, which looks extremely dated in the age of flat design. There are far too many unnecessary design elements and chunky typefaces. The graphs of heart rate and intensity you see after a workout lack the kind of detail I find useful in assessing how successful I was in spiking my heart rate. While other users might be satisfied with the Willpower score, I suspect that anyone advanced enough to want the Armour39 will want to look more deeply at the data.

I was very pleased with the MapMyFitness integration. The test version of the MapMyFitness app seemed to take less time to recognize and pair with the Armour39 module than Armour39’s own app, and its charts gave me more of the level of detail I like. MapMyFitness also has superior social sharing features, so I can broadcast my workout to a set of friends or to the world. (I know most people won’t care, but I have a few buddies who have asked me to motivate them to work out by mentioning them on Twitter every time I go to the gym.)

When I got everything working, the combination of the Armour39 device and the MapMyFitness app was a winning one. And it turns out that the glitches I encountered were due to the unique design of the Armour39 and the unusual testing routines I use on fitness devices, which don’t necessarily match real-world conditions for most users.

Glitches That Enlighten

Since I test a variety of heart-rate devices and apps, I like to benchmark them against each other, running multiple apps simultaneously and switching devices frequently. While experts from the Bluetooth SIG, the organization behind the wireless standard most fitness devices use, have assured me this benchmarking practice should work in theory, in the real world, I’ve experienced a lot of app crashes and failures to connect with various devices.

My tests led to a frustrating result: The Armour39 device would work with one app but not another. When I upgraded to the latest beta of MapMyFitness, which had previously worked when I was broadcasting my heart rate to multiple apps at once, the Armour39 device connected to MapMyFitness but not Pear Sports, another app which delivers particularly good heart-rate charts. And surprisingly, after upgrading to the MapMyFitness beta, which had previously allowed other apps to grab onto the Armour39’s heart-rate signal at the same time, the Armour39 module refused to connect to the Armour39 app.


The Armour39 module lights up blue when it pairs with your phone.

I spoke to Under Armour’s Oleson, who had reasonable explanations for the glitches I encountered that deepened my appreciation for the device. Because while Armour39 will function with other apps as a basic heart-rate monitor, it’s actually capable of much more.

“We do follow the standard [Bluetooth] heart-rate profile, but we have 18 or 19 other profiles as well,” Oleson told me. Those additional profiles—Bluetooth’s term for data specifications—allow Armour39 to calculate a Willpower score and more closely track a workout.

In order to transmit those profiles, Armour39’s module has a more formal process for connecting with a smartphone app: “We are a little more rigid with our handshakes. There are some apps that will connect right away.”

Until its latest upgrade, MapMyFitness was one of those apps. The version I tested engages in the same kind of “handshakes” as the Armour39 app, allowing it to capture the device’s richer workout data. But after it’s gone through this handshake process, Armour39 simply won’t pair with other apps.

Under Armour suggested I manually unpair the Armour39 device from the MapMyFitness app, and then reconnect it with the Armour39 app. That fix worked like a charm.

Sweating The Connection

The other major glitch I encountered was with the Armour39’s initial heart-rate reading. For the first few minutes of a workout, it might display a heart rate that was extremely high or low. My heart rate is normally 60 bpm at rest and around 160 at near-peak exertion; I’d see readings as high as 200 or as low as 40 from the device.

Oleson said many heart-rate monitors experience “noise” from the body’s heart-rate signal as the electrodes make contact. As you sweat, however, the connection with the device improves.

Experienced chest-strap users know a dirty little secret: Wetting the strap with your own saliva is the best way to get a good connection. It may sound gross, but saliva works better than water in transmitting an electrical signal, according to Oleson. (Hey, you’re working out and getting sweaty and showering afterwards—what harm does a little drool do?) If you can’t handle this, washing the device in soapy water or fabric softener is a cleaner way to improve the device’s physical connection—just let it dry without washing off the soap.

Some device makers compensate for this noise by estimating users’ heart rate, which has the effect of smoothing out peaks. Under Armour’s pro-athlete users don’t like that, Oleson said, because they often do quick, intense workouts and want to see their spikes, and they’re also willing to put up with a bit of inaccuracy in the initial readings. Thus, I can chalk up my distrust of the Armour39’s initial heart-rate readings to an intentional design decision, because now that I know that’s how it works, I’m fine with taking that into account.


Under Armour trainer Costa kept me and other participants in a bootcamp at the SXSW Interactive conference jumping.

A Device That Goes Anywhere

Most heart-rate straps stop working when you leave your phone’s Bluetooth range. Armour39 is sophisticated enough to actually store your heart rate and accelerometer data, uploading it to your phone when you walk back into range. That makes it perfect for measuring my heart rate during yoga, where the room is too hot for me to bring my phone.

Here’s the bottom line for me: I don’t think I’d use Armour39 for tracking simple, flat runs or cardio workouts at the gym. But for anything where I’m aiming to spike my heart rate and watch it recover, not just keep it elevated, Armour39 is perfect. And that describes a lot of my workout routine today.

I still have some complaints about Armour39. Even after addressing my oddball testing routines, the pairing process is still imperfect, which I attribute largely to the state of Bluetooth protocols and support for them in today’s mobile operating systems. Every app maker and device manufacturer seems to struggle with it, in my experience.

Oleson concurs: “It’s the Wild West, man.”

I’d also like to see Under Armour do a lot of work on the Armour39 mobile app. Its acquisition of MapMyFitness should come in handy here, both for its software expertise and its large user base. While Under Armour caters to hardcore fitness fanatics and athletes, MapMyFitness caters more to casual exercisers. Under Armour and MapMyFitness together should be able to create a new version of the app that’s more accessible to the masses.

As I’ve written before, heart-rate data is a key biological signal that people can use to improve their fitness. Under Armour has an opportunity to improve the health and wellbeing of a large number of people. Maybe Armour39 isn’t the exact device that will make that leap, but everything I’ve seen suggests Under Armour can build a fitness device that will.

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