Fitness trackers are everywhere these days. They’re built into your gym’s cardio machines, they can be downloaded as an app on your phone, or be worn around your wrist. Unfortunately, most fitness trackers are so wildly inaccurate, their information could be considered guesses at best. However, there are some ways to still use them to your advantage.
So you might be wondering just how inaccurate fitness trackers really are. A quick Google search will result in a number of articles discussing the topic and more studies than you can throw your protein shaker bottle at.
One study at Ball State University compared two fitness trackers worn on the wrist, as well as two more worn on the hip. They compared 30 different adults of different fitness levels while being sedentary, during light activity, and whilst doing strenuous exercise.
While sedentary figures seemed fairly accurate across the board (accurate within 8% or so), 3 of the 4 trackers were off anywhere from 27-34% in estimating caloric expenditure during light activity. And during strenuous exercise, all of them were off as much as 40%.
University of Nebraska researchers compared four different popular brands of tracker, finding them to always be an average of 10-15% off. A study in the Journal of Physical Activity and Health showed one very popular brand to usually be off by as much as 25 calories in either direction. And another study in Medicine & Science in Sports & Exercise found a different popular brand to often overestimate women’s calories burned by as much as 12%.
Fitness trackers are inaccurate for a variety of reasons. The first is that most (especially the accelerometer-based devices such as the ones you wear on your wrist) are based on predictive equations and there are simply just too many variables to take into account.
As an example, you could have two people both standing 5’8”, weighing 155lbs, doing cardio for 30 minutes and taking the same number of steps in that time. However, the calories they burn could still vary wildly between the two based on if they’re male or female, their body fat percentage, training history, level of conditioning, and more. The equations these devices use to predict caloric expenditure just have too much to take into account to provide accurate readouts for everyone.
At the same time, heart rate monitors can be off, too. This is because, as the field of heart rate variability has shown, your heart rate can fluctuate radically – even daily – based on non-workout factors. Higher stress or improper rest could have your heart beating faster / different at rest, which will then translate over into your workout. So even if your heart rate monitor is giving you accurate data, that doesn’t mean the figures it’s using that data to extrapolate are accurate.
While most fitness trackers are wildly inaccurate, that doesn’t mean you can’t still find a way to use them. Steps counted tend to be fairly on point, so you can aggregate that data for yourself, even if just to hit a target number of steps daily.
A heart rate monitor can still show you how much change there is in your heart rate during a given workout, so you can keep yourself within certain “zones” based on how hard you’re wanting to work that day. Some even let you plug in your own data, so if you can become accustomed to how your specific device works, you’ll know what it should read for you to be working how you want / need to work.
Fitness trackers as a whole shouldn’t be relied upon. Depending on which device you’re looking at, they’ve been proven to be as much as 40% off. Most do okay with numbers while you’re sedentary, but the more intense your exercise becomes, accuracy tends to get tossed out the window. That said, they can still be used to monitor some areas of your workout if you know what data to manipulate. Just don’t expect them to replace the scale, mirror, or weight on the bar in terms of your feedback.
As a next read, you might enjoy our write up on the best fitness apps that can actually come in handy.