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Apple Watch and FitBit Light Sensors Don't Work Properly on Dark Skinned and Obese Users

A new study shows that light sensors in wearable devices do not work on people with obesity and darker skin tone. 

Light Sensors Don’t Work on Obese and Dark Skinned Users

The discovery serves as a bad sign for wearables like Fitbit and Apple Watch that are using light sensors for new applications, like monitoring the user’s blood pressure, according to The Verge. 

The author of the study, Jessica Ramella-Roman, an associate professor at Florida International University, said that the device’s architecture needs to change.

The study focused on the photoplethysmography (PPG) signal, which is a technique that uses changes in how light is reflected to measure the user’s blood flow, on three wearable devices: Fitbit Versa 2, Apple Watch Series 5, and Polar M600, as posted on NCBI.

A model was used to simulate how light moves through tissue and demonstrate how the wearable’s light sensors behave with different skin tones.

Since people with obesity have thicker skin, it makes it more difficult for the sensor’s light to go through the body’s tissues. 

Also Read: Meet Fitbit Alta HR: ‘Slimmest Fitness Wristband’ With Heart Rate Sensor

While the previous study on accuracy and bias in wearables has focused on the user’s skin tone, Ramella-Roman said that a lot of studies had not included a lot of users with obesity despite the physiological differences.

The PPG signal of wearable devices decreases 60% if it is used by someone with obesity, while it decreases 10% if it is used by someone with a darker skin tone, according to Nature.

Signal loss appeared to be because of changes in skin thickness in users with obesity. There were changes in the peak of the PPG signal, which is used to calculate the heart rate but whose signal strength should not change based on the heart rate value.   

The shape of the signal changed as well, which different groups are using to track blood pressure. 

Diminishing Signal

The study noted that as they increased the BMI level and increased the user’s skin tone, the signal decreased, and the other features began disappearing too.

The study only modeled how the wearables would detect signals in the lab. The team still has to use the devices on actual people to confirm their findings. They are currently in the process of doing the study, and they have enrolled 100 participants.

However, the issues revealed by studies like this complicate projects looking to use wearables to detect cardiovascular health for underserved groups.

The new study shows that researchers have to be careful in using PPG, especially for projects that aim to monitor the health of people with cardiovascular issues, most of which are associated with obesity.

Wearables also use light sensors to detect flu in users, which may be compromised.

The findings also suggest that other devices that use light sensors and PPG, as the blood oxygen measures in clinics or hospitals, may not work well for people with obesity. 

Related Article: Fitbit Files Patent for Smart Ring That Tracks Blood Oxygen and Pressure Levels

This article is owned by Tech Times

Written by Sophie Webster

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