Addressing Microsoft Band HR Accuracy

One of the things I hear continually in the Microsoft Band communities are complaints about HR tracking accuracy. It gets enough complaint exposure that I think it’s worth addressing here.

Those that follow my Microsoft Band articles here, know that I’m currently in the midst of a process for comparing the Microsoft Band against a stack of other fitness wearables. This process has brought has shed some revealing light on this particular issue.

If you want absolutely accurate HR stats, you need to wear a chest strap. But, who wants to wear one of those 24 hours a day, right? The reason why the chest strap works so much better is not because it’s just a better technology, but really in the way it’s designed so that it rarely loses contact with skin during activity. It’s the connection, or continued connection that’s important.

Wrist-based HR monitoring is performed through a light sensor that sits directly against arm skin on the underside of a fitness wearable. Microsoft, with the Band, wasn’t the first to do this, but has been one of the more successful. And, because of this, has led others (Garmin, Fitbit, others) to do the same.

Wrist-based HR monitoring works great as long as the landscape of your arm never changes. Unfortunately, however, whenever you change the shape of your arm, and the light sensor loses connection, it will alter the accuracy of the sensor. This issue is not solely a Microsoft Band problem, but affects any manufacturer’s device that has a light sensor for wrist-based HR monitoring.  

So, how do you change the shape of your arm? That’s pretty easy, actually – and pretty unfortunate that it’s so easy to do. Changing your grip on your bike’s handlebars so that your wrist is bent instead of straight – that does it. Bending your wrist to do a barbell or dumbbell weight curl – that will do it. Doing something as simple as performing a standard pushup where your hands are bent backwards – that can cause it, too.

As a Microsoft Band owner, though, you can rest assured that – even though you are seeing some accuracy discrepancies – the Band does its best to compensate and is probably the most accurate of the lot I’ve been testing, but only when worn with the watch face underneath your wrist. The HR sensor is most accurate when in contact with the bottom side of your wrist. The majority of other fitness wearables are designed to be worn more like a standard watch and don't even work right when worn on the underside of the wrist due to action button locations, etc.

Obviously, though - if your Microsoft Band's HR reporting is totally whack, get it replaced. That sensor can go bad.

All that said, wrist-based HR monitoring definitely needs to be improved in the future. Interestingly, I’ve actually found that the Bragi Dash wireless headphones do a better job monitoring HR through your ears than these others do through the wrist.

Even Garmin will tell you that wrist-based HR monitoring is an inaccurate technology. Here's what Garmin has to say on the matter:

While our wrist HR monitor technology is state of the art, there are inherent limitations with the technology that may cause some of the heart rate readings to be inaccurate under certain circumstances. These circumstances include the user’s physical characteristics, the fit of the device and the type and intensity of the activity...