How accurate are wearable technology trackers?

I love gadgets, I love training with data, and I love comparing results and tracking my progress.

So this week just gone I decided to do an experiment to see if we should believe everything we are told by watches, activity trackers and the good old treadmill.

In my first test, I ran 5 km on the treadmill. I also wore my Apple Watch, and my Garmin 920XT with heart rate (HR) monitor. As I was inside, both the devices were going off motion sensor rather than GPS.

The results were as follows:

Treadmill: Distance 5km, Time 24″56, Calories 390, Average Pace 4’53” km

Apple Watch: Distance 4.78km, Time 24″51 (I started it a tad late!), Calories 286, Average Pace 5’11” km

Garmin 920XT: Distance 4.69km, Time 24″43, Calories 276, Average Pace 5’17” km

Apple Watch 5km indoor run data Garmin 920XT Indoor 5km run data

As you can see, the distance on both trackers were dramatically less than the treadmill (how did I lose 300m?!), and as predicted the treadmill highly overestimated my calorie expenditure. I hadn’t put in any personal information such as height and weight, so it was giving me the generic calorie consumption. If you want a more accurate calorie measurement, then using your HR is always best.

I then took my experiment outside, using the GPS on my Garmin watch, but leaving the apple watch to calculate using motion tracking.

Garmin 920XT: Distance 5km, Time 23’54”, Calories 314, Average Pace 4’47”

Apple Watch: Distance 4.61km, Time 24’01”, Calories 272, Average Pace 5’12”

Garmin 920XT 5km outdoor run data Apple Watch 5km Outdoor run data

It seems that the Apple Watch greatly underestimates my distance covered. This could be because it is misjudging my stride length, and therefore expecting me to have covered less distance, which in turn effects calorie expenditure. However, it also means that the run on the treadmill was potentially over the 5km (and the treadmill could be calibrated wrong), as the Apple Watch underestimated by more when outside, and GPS is the most accurate at measuring distance.

It just goes to show you cannot always believe what you are reading on the screens you rely on!

My key takeaways are as follows:

  • GPS is your most reliable and accurate way of recording distance and pace.
  • Never believe the treadmill calorie expenditure! Always measure using your Heart Rate.
  • Use these training tools as a guide, but try and learn how you feel when running at certain paces, so you can judge your speed without relying on technology.
  • Enter races and organised events as a way to test yourself against the clock.
  • Just because your apple watch says you’ve walked 20km today, it isn’t necessarily right. In fact, according to my studies, I would’ve probably walked further!

If you’ve tried and tested any other trackers and want to have your say, then share your thoughts here!

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