Apple Watch is gaining more and more popularity every year. If earlier watches could be found only among apple geeks, now it seems that every third iPhone owner has a wearable device on his wrist. Whoever says anything, the Apple Watch was created primarily to monitor your health: it counts calories, writes an ECG, measures your pulse, and some even know how to assess the level of oxygen in the blood. Even if you initially bought a gadget for purposes other than performance monitoring, it won’t take a year before Apple will force you to pay attention to these chips. At the same time, I think that many would be interested to figure out how here heart rate monitor works or how Apple Watch counts calories.
Personally, I have little confidence in the indicators on the watch. After all, Apple itself says that the Apple Watch is not a medical device and does not claim colossal accuracy. But if we look from the other side, we must understand that the postscript “medical device” is not only dozens of scientific studies, but also coordination with the Ministry of Health and a bunch of other bureaucratic issues.
How Apple Watch Counts Calories
For starters, it’s worth saying that the red activity ring is responsible for burning calories. This is not to say that the rest of the rings are not worth paying attention to, but if you are interested in calories, the red ring is the main thing. Do not forget that Apple Watch does not count everything, but only active calories. They, unlike sleeping ones, are burned only during physical activity. The watch does not take into account many parameters: mental activity, physiological needs, and so on. Their indicators cannot be used to plan a diet.
On the official website, Apple indicates that Apple Watch uses personal data to calculate the number of calories burned. We pass in the Watch app, My watch, Health info, and look at what medical data we specified during the first setup: age, gender, height, weight. You set these parameters yourself, and the watch already superimposes other indicators on them: distance traveled and speed, training mode and duration, heart rate, breathing rate, oxygen level in the blood.
Here, Apple asks to indicate the use of a wheelchair (in order to more accurately determine physical activity) and some drugs that affect cardiovascular performance, and therefore calorie count. Children grow up, adults get fat (or lose weight). To make your Apple Watch measurements more accurate, try to update this data regularly. The watch cannot do it for you.
How Apple Watch measures heart rate
In contrast to the number of calories burned, with heart rate monitor on Apple Watch everything is more or less clear. On the back of the smartwatch there is a special sensor that works on the principle of photoplethysmography.
I think many have noticed a green glow when measuring. So, there are two elements in a watch: a green LED, which illuminates the blood, and a photodiode, which reads the reflection. During each contraction of the heart, the volume of blood entering the vessels increases, and in the interval, on the contrary, decreases. These parameters are registered by the sensors. This method allows you to determine the number of heartbeats in the range from 30 to 210 beats per minute.
Accordingly, the greater the distance between the watch and the wrist, the brighter and more often the LED works. That is why for the sensor to work properly, the watch must fit snugly on the wrist. We have already talked about how to properly wear Apple Watch in our Yandex.Zen, you can familiarize yourself with it.
In 2017 Stanfaird University did a whole research, where he described in detail the quality of the heart rate meters in wearable devices. It turned out that the error of Apple Watch is 2%, which is a very high indicator. But the numbers, as I have already said, are of little importance for doctors, because until a special organization (for example, the FDA) approves the device as a medical device, it is of little use in practice.
It is especially important to measure your heart rate during physical activity. As soon as you activate training mode on the watch, the sensor starts to work continuously, which ensures high accuracy of the readings.
How Apple Watch measures breathing rate
With watchOS 8, Apple smartwatch users have the ability to take control of their breathing rate. On the official website, Apple only says that Apple Watch uses a built-in accelerometer to measure respiratory rate.
With it, Apple Watch can measure the movements your wrist takes as you inhale and exit. This is why Apple’s smartwatches can only measure respiration rates while sleeping. There is no data for the measurement accuracy, but I managed to find some research on this score, where the respiration rate was estimated depending on the position of the wrist. The error was only 0.38 breaths per minute, which is comparable to medical devices used in practice and approved by special organizations.
How Apple Watch measures blood oxygen levels
Blood oxygen measurement technology works in much the same way as heart rate measurement – using reflected light. Even at the presentation of Apple Watch 6, the most attentive users noticed that in addition to green LEDs, there are also red ones. Plus, there are much more sensors here. There are already 8 of them (4 LEDs and 4 photodiodes).
Let’s not go into the intricacies of medical science, and let’s just say that blood absorbs red and infrared light differently depending on the level of oxygen saturation, so the light that reflects on a special photodiode in the watch allows Apple Watch to determine the color of your blood, and therefore the oxygen level in it.
Not so long ago, we told you about studies that described the accuracy of measuring the oxygen content in the blood of the Apple Watch 6, where the sensor was compared in detail with a medical pulse oximeter, but these indicators are still far from ideal. You can check it yourself.
How to measure blood pressure on Apple Watch
Alas, but for now Apple Watch is unable to measure blood pressure… In any case, no such function has yet been announced. At the same time, the same Samsung Galaxy Watch 4 has the function of measuring blood pressure and does it using the same sensors that are used to monitor the heart rate. Only they do not look at the frequency of reflection of the blood flow, but the volume.
Apart from the accuracy, about which little is known, this chip has one significant drawback – the need for constant calibration of the device. Owners of Samsung smartwatches have to carry out this procedure every 4 weeks.
Plus, given how Apple bothers about the error, it is possible that Cupertino considers such measurements to be insufficiently accurate and that is why they do not implement the chip. But these are just my guesses.
Source: AppleInsider.ru — крупнейший сайт о iPhone, iPad, Mac в России by appleinsider.ru.
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