WOOO!! What a fantastic workout! You are dripping in sweat, sore, and barely have any energy left. Even better, your fitness tracker is displaying a new high! Eight hundred calories burned in 30 minutes!!
But how accurate is that number?
Tired of fitness misinformation? Read our article “weight loss myths,” where we debunk a lot of the misinformation about losing weight and getting in shape.
Researchers at Stanford University looked at the accuracy of seven fitness trackers on heart rate and calories burned (1):
Mio Alpha 2
Samsung Gear S2
The study was composed of sixty volunteers: 29 women and 31 men.
Participants wore four trackers at a time while being continuously monitored to collect the data on how many calories they were burning.
The study was made up of (get ready for this):
Sitting for 5 minutes, followed by 10 minutes of walking on a treadmill at three mph and .5% incline, followed by walking even faster (4 mph at .5% incline) for 5 minutes, then running at a slow pace (avg. 5.7 mph at .5% incline) for another 5 minutes, then running at an average of 6.9 mph at a .5% incline for 5 minutes.
After ALL of that, participants would sit for a minute and then rest for two more minutes.
But wait! There’s more!
After the 2 minutes, participants were asked to ride an ergometer ( fancy stationary bike) for 5 minutes at a low intensity.
Then by a higher intensity for another 5 minutes and finally a 1-minute sitting recovery.
We should also mention both sections of this study were individualized to the participant’s fitness levels.
JESUS CHRIST! I feel like if I had been a part of this study, I would have fallen flat on my face once the researchers told me to run. ( yes, we are also confused as to who would volunteer for something like this…but I guess it’s for Science, right?)
Heart Rate Results
The fitness trackers displayed the lowest error measuring heart rate during the cycle ergometer portion of the test, with a median error of 1.8%.
Six of the seven trackers achieved a median error below 5%. The only tracker out of this range was the Samsung Gear S2, with 5.1%.
The highest error displayed was during the walking portion, with a median error of 5.5%.
Three out of the seven fitness trackers achieved a median error of below 5%: The apple watch, Pulse On, and the Microsoft Band.
The remaining four devices achieved a median error of between 6.5% and 8.8% — no Bueno.
When it comes to heart rate accuracy, the Apple Watch was the best, while the Samsung Gear S2 was the worst.
Another interesting finding was that there were higher errors in heart rate between volunteers who had a darker skin tone, a higher body mass index, and a larger wrist circumference. (Well, I guess I’m screwed lol.)
Calories Burned Results
I’m sure this is what you guys have been waiting for!
And this is where the pros for getting one of these fitness trackers end.
All of the fitness trackers were wildly inaccurate at measuring calories burned.
The median error for the devices ranged from 27.4% (Fitbit) to 92.6% (PulseOn).
The lowest relative error across fitness trackers was achieved during the walking (31.8%), and running ( 31% ) portions of the test. While the worst, surprisingly, was during sitting parts of the study (52.4%).
The Apple watch was the most “accurate” of the activity trackers, while the Samsung Gear S2 was the worst (Wtf Samsung?!).
Fitness trackers can be accurate when it comes to measuring heart rate, but horribly, horribly inaccurate when it comes to measuring energy expenditure.
Another study on the Fitbit One, Fitbit Zip, Fitbit Flex, Jawbone UP24, COSMED K4b2, and Omron HJ-720IT, found that these devices exaggerated calories burned by 16% to 40% during activities like jogging, walking, and climbing stairs (2).
A systematic review and meta-analysis of 60 studies looked at the accuracy of energy expenditure measured by fitness trackers.
Researchers found that the activity trackers were very inaccurate, with the MOST ACCURATE trackers still having errors of between -21.27% and 14.76% (3). OUCH!!
As you can see, research shows that fitness trackers are not very accurate when it comes to calories burned. This is especially troublesome when apps like myfitnesspal now allow you to sync up with fitness trackers and encourage people to eat the calories they’ve burned.
Are we saying that these have no use? No, we are not. When it comes to heart rate and calories, most of these have a pretty significant error margin. When it comes to steps, they seem to be a little more accurate. Our point is to remain mindful and to remember that these trackers can serve as a guide of some sort, but should not be 100% depended on.
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