Many of us rely on fitness trackers to measure things like our heart rate, step count, and sleep quality, but are they really accurate? The answer depends on the health metric you're looking at. Most of them can give you a good idea of your step count if you're hiking, but even the best fitness trackers struggle to accurately record when you're asleep and when you're awake.
We've reviewed the latest studies and talked to experts to find out which metrics you can really trust.
Calories
A 2018 study by researchers at the Technical University of Munich found that fitness trackers were woefully inaccurate when calculating energy expenditure (calories burned). The damning report concludes that the trackers are not accurate enough to be used in sports or healthcare.
SIX3NINE personal trainer Emily Taylor explains why some trackers may not be accurate for calorie expenditure: "Many different factors come into play when estimating calorie expenditure, and not all of them can be accounted for by the formulas these trackers use to predict energy expenditure.
Some fitness trackers only count the number of calories you burn during exercise, while others look at calories burned throughout the day. It can be helpful to look at calories burned as a kind of guide, showing the days when you had the most active periods, but don't rely too heavily on this if you're trying to calculate calorie intake versus energy expenditure.
step tracking
Most wearable devices use motion sensors to track how many steps you take, but studies have shown that their pace can affect accuracy.
A 2020 article published in the International Journal of Environmental Research and Public Health found that long, brisk walks were calculated more accurately than shorter walks. So your watch might count your steps on a walk, but it won't record your movements around the house. A different 2017 study, published in the peer-reviewed journal JMIR mHealth and uHealth, found that the accuracy of fitness trackers was negatively affected by walking aids such as a cane or caddy.
No studies have been able to conclude that trackers are 100% accurate when counting steps, so you may also want to take this measurement with a pinch of salt, but it's generally more accurate than recorded calories and weight.
Heart rate
“Some trackers use an ECG heart rate belt, which measures heart rate using electrical waves, while others use an optical heart rate monitor that measures heart rate with light,” says Mari Thomas, founder of Maaree sports bras and a former tester of TomTom fitness trackers. "Optical heart rate is the less accurate of the two because external rhythms, such as running cadence, can interfere if they line up too closely."
A 2017 study from the Heart and Vascular Institute tested fitness trackers and monitors worn on the chest with a standard ECG. The researchers used a sample of 50 people and measured their heart rates with fitness trackers while they walked and ran on the treadmill. They found that monitors worn on the chest had the most accurate and consistent ECG readings.
Thomas explains why fitness trackers can be less accurate: "The surface of the wrist needs to be in close and constant contact with the receiver, which can be difficult if one has a smaller or more difficult service area here.
"Perfusion can also play an important role, and low perfusion will have a detrimental effect on OHR performance. Factors that affect perfusion can include skin tone and outside temperature.
Sleep
The most accurate way to get a reading on how well we sleep is to take a polysomnography test, which measures things like brain waves and heart rate to get an overall picture of sleep health.
Fitness trackers typically use sensors to measure our movements while we sleep, but some research indicates that their sleep tracking doesn't compare to traditional methods, especially when it comes to measuring our sleep cycles, including deep, light, and deep sleep. REM (rapid eye). movement).
A 2019 study by researchers at the Yale Schools of Nursing and Medicine showed that when fitness trackers record sleep and wake times, they are only 78% accurate. And the same study found that trackers were terrible at recording when users fell asleep, with only a 38% success rate.
Despite the vagueness of fitness trackers, however, Emily says they're great for one thing: "Trackers can provide the accountability and motivation needed to implement positive behavior change. Having a quantifiable goal by which to work (such as a step count and sleep goal)) can be very valuable.”
