The light sensors used in 'wearables' are less accurate in people with dark skin and those with obesity. These results have been confirmed in a study carried out at the Florida International University by Professor Jessica Ramella-Roman.
Among the devices studied we have the Apple Watch Series 5, Polar M600 and the Fitbit Versa 2. These devices have been shown to have less accurate responses in their sensors when used in people with dark skin and those who are obese.
To carry out the study, Professor Jessica Ramella-Roman looked at the signals produced by the photoplethysmography (PPG) techniques; a technique that allows the heart rate to be measured by taking into account the light reflected by the blood. The team also used techniques to simulate the movement of light on the skin of a hypothetical patient; this helped them figure out how wearables would behave depending on variations in skin properties.
Dark skins have a higher concentration of melanin than light skins, so they absorb a greater amount of light. On the other hand, the skin in people with obesity is usually thicker; with less accumulation of water and less blood flow than that of those who do not present obesity. Ramella-Roman assures that many studies on the reliability of these wearables and sensors have not included obese people in their sample population; despite the clear differences in composition.
The architecture of these sensors must change
Photo by Jair Lázaro on Unsplash The study concluded that, in people with darker skin, the response of the three devices varied by less than 10 percent. However, when obesity is studied together with a dark skin tone, the accuracy dropped to 60 percent reliability. The Apple Watch, meanwhile, managed to have the highest reliability; while the Fitbit Versa 2 (which has fewer sensors), had a more dramatic loss in its signal.
As we increased the BMI level and the skin tone, the signal decreased, and then other features began to disappear as well…
Professor Jessica Ramella-Roman The team in charge of studying the sensors of the Apple Watch and other wearables still has the task of confirming its findings in patients of flesh and blood. So far, approximately 100 people have joined to participate in the analysis, and they have already started to work. The results warn researchers to be careful when using PPG; especially when carrying out studies that seek to help people with cardiovascular problems, a group that includes part of the obese population. Ramella-Roman comments on the latter that “The holy grail in this context is looking at blood pressure… But many, many studies look at blood pressure using a combination of PPG and other modalities” .
The solution in wearables is quite simple Ramella-Roman also assures that, although many of these wearables were designed without taking this part of the population into account, “ changes can definitely be made. I don't see anything that can limit that.” The solution could be to improve the distance between the sensors; this would allow greater accuracy in people with darker skin tone or obesity, without compromising overall accuracy along the way.
Therefore, wearable manufacturers will have to dedicate greater efforts to improve the reliability of their sensors in order for them to work correctly with their entire user base.
