How Smart Is Your Smartwatch?

Let's dive into the world of wearables, smartwatches, fitness bands, movement trackers, or whatever you want to call them to find out how much or little you can actually rely on them.

Brock Armstrong
7-minute read
Episode #347

Second Test - Heart Rate Measurement

To test heart rate, he peddled on a stationary bike to get his heart rate up to a consistent 140 beats per minute (BPM). He measured this by actually putting his hand up to his carotid artery and taking his pulse - old school like. He did this two days in a row, again being more scientific than I would have been.

The different heart rate monitors all appeared to have their own issues. Some needed time to catch up, even though his heart was already rocking at 140 bpm. Other devices would flip around between a low heart rate like 90 and a reading closer to what he got from his manual count, like 130.

As was expected at the time, the heart rate tracking was the least reliable of the three tests he did. The closest devices were the two Apple Watches. Both of them read 137 and 134 bpm, which is pretty darn close to the manually counted number.

Third Test - Total Distance Travelled

To test distance, he got on a treadmill and walked half a mile. Which doesn’t seem like much but even such a minimal distance was enough to see big deviations in the data.

What’s kind of cool is that since he was wearing multiple watches at the same time, he actually could see the distance totals diverge right in front of his eyes. The more he walked, the more the watches showed their inaccuracies.

In the end, the Withings Pulse O2 apparently nearly matched what the treadmill said. Though I would say that the treadmill itself was likely also wildly inaccurate (ones in public gyms usually are) and if that’s the case, then who knows which device was actually “right.”

Relative Comparison

In the end, what I take away from all of this is that maybe the best thing to do is to simply use these devices for relative comparisons. You need to commit to using one device and stick to it; the direction of the trend that is more important than the number itself. Just like a daily weigh-in on your bathroom scale, the number you see each day isn’t as important as the overall trend is.

In the end, what I take away from all of this is that maybe the best thing to do is to simply use these devices for relative comparisons.

I don’t know about you but when I weigh myself, I use the same scale that I have had for 7 years. I get out of bed, go to the bathroom, empty my bladder, and before I have my coffee or breakfast, I strip down to my birthday suit and get on the scale. I aim to be as consistent as possible and don’t concern myself with the actual pounds, kilos or percentages but rather I wait until the data is uploaded to my fancy charting software to see which way I am heading.

To further illustrate this, I recently had two separate DEXA scans done and both times, both technicians at the labs said that they had never in all their years of doing these scans, seen someone with a single digit body fat percentage. While a friend of mine had a magnetic resonance imaging (MRI) done that showed he was something close to 3 percent body fat. And to drive the point home even more, even my own measurements between my Tanita electrical impedance scale and the DEXA scan showed a difference of 3 percent within a 3 hours time frame.

What the Makers Say About This

Even a spokesperson from Garmin said that's it's about an individual's relative gain and that Garmin activity trackers are designed to help users develop healthy habits and motivate them to beat yesterday.

A representative of Fitbit stood by the company's research and product testing but cautioned against putting too much stock in the exact figures.

Polar pointed out that physical activity comes in many forms, each of which can provide benefits and what's important to remember is that the reason we're tracking steps isn't just for the sake of tracking them, but ultimately because it's about achieving a better fitness result.

Another company (which declined to be named) suggested that there’s always going to be a variation for each statistic. For steps, some devices treat hand movements differently, so if people wave their hands a lot during the day, they might get credited differently depending on the device.

So, I guess it kind of goes without saying, but these tests are pretty big strikes against the wearables, at least for energy burn tracking. So if you’re doing your best to count every last calorie (which I honestly don’t advise), definitely don’t take your wearable’s word for it.

Whether or not my Garmin, Apple Watch, or my bathroom scale is truly giving me accurate data, I am still more interested in seeing my numbers improve than I am in putting a lot of stock in whether I burned precisely 400 calories, ran exactly 3.10686 miles (5k) or that fat truly makes up 12.23 percent of my body. When I see my scale display "11 percent," I will celebrate - not because of the actual number itself but because I am moving in my desired direction.

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About the Author

Brock Armstrong

Brock Armstrong is a certified AFLCA Group Fitness Leader with a designation in Portable Equipment, NCCP and CAC Triathlon Coach, and a TnT certified run coach. He is also on the board of advisors for the Primal Health Coach Institute and a guest faculty member of the Human Potential Institute. Do you have a fitness question? Leave a message on the Get-Fit Guy listener line. Your question could be featured on the show.