screenrant.com Apple Watch & Fitbit Accuracy Affected By Skin Tone & Weight, Study Says

Yet another medical research says light sensors on fitness wearables like the Apple Watch and Fitbit bands don't always provide an accurate reading when worn by obese people or those with dark skin. Brands like Apple and Samsung have often claimed that their wearable devices have been tested comprehensively on subjects across varied age groups, ethnicity and body types, but now and then, a study with empirical data pops up to question those claims. For example, patch placement and motion affect the readings from sensors, but ideally, factors such as skin color should not if the test spectrum is as broad as these companies claim.

The most common type of sensor used by wearable devices relies on an optical measurement technique called photoplethysmography (PPG), which involves measuring the heart rate by analyzing the volume change in arteries via light passing through the skin. When light falls, some of it is absorbed by the blood in arteries. And as the blood volume changes, the intensity of reflected light also changes, and this variation is what the PPG sensors detect to measure heart rate. Unfortunately, multiple studies have found that heart rate sensor readings tend to be biased for dark skin.

Related: How Apple Watch Measures Heart Rate & Its Accuracy Explained

Now, another study from Florida International University's Department of Biomedical Engineering has revealed that wearable devices from Apple and Fitbit falter more frequently when it comes to people with obesity issues or those with a darker skin tone. As part of the study, the team tested Apple Watch Series 5 and the Fitbit Versa 2 to measure their sensor's reliability using the Monte Carlo Method of analysis to study the PPG data. Specifically, the team relied on looking at the AC to DC (AC/C) signal ratio extracted from the PPG waveform over the wrist. The team found that the type of skin tone varies the sensor readings by 10 percent. Furthermore, when the obesity factor is thrown into the mix (both solely or with skin tone), the signal varies by 61.2 percent.

A Long-Running Weak Spot

Signal loss observed during the study can be attributed to the skin thickness and chemistry, as per the study. Thicker skin layers, which are a result of higher Body Mass Index (BMI) due to obesity, led to higher signal loss during the simulated tests. While that might sound very technical for an average person, the critical finding here is that sensors used in wearables like the Apple Watch and Fitbit are not universally capable of providing an accurate reading for non-obese (NOB) and morbidly obese (MOB) people. "Our study has shown that the shape of the PPG signal is strongly impacted by obesity and skin tone," says the paper listed on PubMed Central (PMC) archive of the U.S. National Institutes of Health's National Library of Medicine.

However, this is not the first study to document the problem, and heart rate is not the only metric on which these wearable devices tend to provide unreliable data. An analysis by The Washington Post on the Apple Watch Series 6 and the Fitbit Sense smartwatches also exposed that these wearables might not be the most reliable for calculating metrics like blood oxygen saturation levels. In addition, a Stat study from 2019 found that Fitbit and Samsung wearables struggle with darker skin tones. The likes of Garmin and Fitbit have tried to boost the intensity of green light emitted by the sensor to get over the melanin, or even tattoo, hurdles, but the issue persists.

Next: Apple Reportedly Testing AirPods With Temperature Tracking, Health Features

Sources: NCBI, The Washington Post, Stat

Nadeem has been writing about consumer technology for over three years now, having worked with names such as NDTV and Pocketnow in the past. Aside from covering the latest news, he also has experience testing out the latest phones and laptops.When he's not writing, you can find him failing at Doom eternal.