Why is your smartwatch not so smart about calorie consumption …

When trying to get the most accurate reading of the energy consumed during exercise, professionals often look to tools such as: Metamax 3B..

Like its SF sound name, it registers various characteristics of a person’s breathing, the heart, lungs, and the rest of the blood vessels and metabolic system while the body is under physical stress.

It is not a consumer grade product, as it is accurate and validated among researchers. And even so, it’s not like you want to carry around in your morning run in your neighborhood or gym. It’s not the time to hit a watch that knows not only your heart rate, but also the number of calories you’re burning.

However, Metamax 3B was the tool of choice for a team of Canadian researchers seeking to test the accuracy of wearable fitness devices for consumers. study It was published in January 2022.

They examined the accuracy of heart rate measurement and energy consumption (calorie burning) on ​​three high-end devices, the Apple Watch 6, Fitbit Sense, and Polar Vantage V, and compared that accuracy with the measurements provided by Metamax 3B. The same goes for the Polar H10, a consumer heart rate monitor chest strap.

They conducted a survey of 60 participants, evenly divided into men and women between the ages of 18 and 30, all physically active non-smokers with an obesity index of over 30. There was nothing, it was all white.

Heart rate measurement accuracy, skin color, weight

Although not explicitly stated in the paper, it is safe to speculate that the exact selection of white candidates is due to previous theoretical discoveries in many such studies. 2021 studyWe have found that consumer wearable heart rate sensors are likely to be inaccurate if you have dark skin. Smart devices such as those mentioned above usually rely on optical sensors to continuously monitor blood volume.

Between heartbeats, the blood volume on your wrists decreases.

However, unlike the heart rate trackers used in hospitals that use infrared sensors, watchmakers primarily use cheap green light sensors, and some use infrared on a regular basis. Green light has a short wavelength and is easily absorbed by melanin in dark skin.

The researchers behind the above study also found that sensors are inaccurate for obese wearers because obesity can affect blood flow and the thickness of various layers of skin. did.

In fact, they found that skin tone changes the sensor signal by less than 10%, but the combination of dark skin and obesity causes 61.2% loss of signal from the watch’s sensor. became.

Other studies have been conducted on young, Caucasian, physically active participants with a BMI of less than 30, and all three watches (Apple Series 6, Fitbit Sense, Polar Vantage V) are relatively accurate. I found out. Heart rate monitoring across a variety of physical activities, including sitting, walking, running, cycling, and resistance exercises.

They found that the Apple Watch was the most accurate for measuring heart rate over all five activities, while the other two had different levels of accuracy depending on the activity.

Calorie Burning: Overestimated? Underestimated?

The amount of calories burned during an activity depends on the amount of energy consumed, and the amount of energy consumed itself depends largely on many factors such as weight, height, gender, age, body composition, and the nature of the activity.

Estimated calorie consumption on a gym machine can be ignored based solely on the various factors that affect energy expenditure. But what about wearable devices that process much more data?

Unlike heart rate monitors, which turned out to be relatively accurate, calorie burn measurements were found to be significantly inaccurate, at least for non-obese Caucasians.

on average, studyApple Watch underestimated energy expenditure of 103 calories per hour, Polar Vantage 63.6 calories, and Fitbit Sense 130.8 calories.

Sure, knowing that they’re burning more calories than they thought might be welcome news for anyone trying to burn more calories, but gaining and maintaining weight. Not so many for those who are trying.

These findings regarding the inaccuracy of calorie burning measurements are not new.

Numerous independent studies have accurately tested different smartwatches and reached similar conclusions, but some results may indicate overestimation rather than underestimation.

Take this, for example 2020 research This gives Apple Watch a 58% chance of overestimating calorie consumption, Fitbit a 39.5% chance of overestimating it, a 48% chance of underestimating it, and a Polar device having a 69% chance of overestimating it. Garmin devices have a 69% chance of underestimating. time.

Simply put, wrist-worn devices may rely on many health-friendly features, such as apps that support health and physical activity, but consume regardless of the manufacturer’s promise. Accurate counting of calories is not one of them. DM / ML


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