Recent smartwatches offer much more than just a pedometer. They are now used to measure heart rate, but also the VO2max, the SpO2 and even the ECG. We explain all this to you.

It seems a long time ago when the manufacturers of connected watches and bracelets offered only simple pedometers attached to the wrist. From now on, manufacturers offer a multitude of sensors and collect or analyze a lot of data about your health. Even the most accessible models now include a monitor for your heart rate. On the most high-end watches, sometimes we will even find an electrocardiogram. Sometimes, we can even have measurements that may seem more complex such as SpO2 or VO2max.

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But what is all this data? ? What do they measure and how can users use them to improve their health and possibly their athletic performance ? This is what we will see in this file.

The heart rate is the main data measured by connected watches and bracelets. Most of the time, this measurement is made with a fairly simple tool, the heart rate monitor. It is in fact a sensor, attached to the back of the watch or bracelet, who will use a principle with a complicated name to say the least, photoplethysmography.

Concretely, the heart rate monitor has two purposes : send pulsed green light, and measure the amount of reflected light. This is photoplethysmography. The more green light is reflected, the more it means that your blood flow is important, and therefore your heart beats at a high rate. If your heartbeats are spaced apart, then you will have lower blood flow and the green light will be absorbed more by the skin. This is why the heart rate monitors in watches and bracelets send out light at a very high rate, to know the variations in blood flow and therefore be able to give a measurement as close as possible to your real heart rate.

As for pulse measurement, the heart rate monitor will give you a measurement of your heart rate in number of beats per minute. The resting heart rate of a healthy person is generally estimated to be between 50 and 80 beats per minute. However, in activity, the pace will necessarily increase. It is in this context that connected watches and bracelets are most useful.

Indeed, manufacturers sometimes offer continuous monitoring of your heart rate, or even an even more precise trace throughout your training session. What to compare these data with other elements such as the difference in height or the pace of walking. Mostly, heart rate is an excellent indicator not only of its level of health, but also its sports performance.

Often, the goal of cardio training such as running or cycling is precisely to vary the heart zone, between light intensity, moderate intensity or strong intensity, for example in interval training. The reserve heart rate corresponds to the ideal heart rate on which you must remain fixed during your exercise for good efficiency..

More and more, one sees appearing among the various data measured by the connected watches and bracelets a certain "VO2max". This is particularly the case with the latest versions of the Apple Watch, les Apple Watch SE et Apple Watch Series 6.

However, Apple is not the only manufacturer to offer this type of measure, since they are available on the Samsung Galaxy Watch 3, la Huawei Watch GT ou le Xiaomi Mi Band 5.

It must be said that qualifying the VO2max as a measurement is a misnomer, since connected watches and bracelets do not actually measure it, but just calculate it. To understand it, just explain that the VO2max corresponds to the maximum volume of oxygen that can be absorbed. In other words, so this is the maximum oxygen consumption, expressed in liters of oxygen per minute per kilogram (L / min / kg).

In the facts, many manufacturers, however, are content to offer a more graphic approach, with a dial showing the level of VO2max and a slider pointing to the level - low, way, Student, etc. A good VO2Max is generally considered to be in the order of 45 ml per minute per kilogram in men and 35 ml per minute per kilogram in women.

To accurately measure VO2max, sports institutes use a treadmill system with a mask that measures the flow of oxygen inhaled by the runner at their highest pace. Suffice to say that this type of measurement is not supported by sports watches and bracelets. They simply combine the different data recorded, like heartbeat, the age, the weight, gender or gait to derive a calculated VO2max, which will therefore be less accurate than in the laboratory. To do this, two methods exist, demanding to run as quickly as possible during 12 minutes. Once this period has passed, the watches measure the distance traveled and deduce the VO2max from it using two formulas :

Given its very purpose - to measure maximum oxygen uptake - VO2max cannot be calculated at all times. The data is therefore often only available when you are in training mode on your watch or your bracelet, since your heart rate must be particularly high.

Concretely, the VO2max will allow you to know your performance in terms of endurance. The higher the VO2max will be, the more you will be able to assimilate oxygen, the less quickly you will tire. As for the heartbeat, it is therefore an indicator to monitor as you train in order to improve it in order to be more and more enduring.

If the name of SpO2 may seem close to that of VO2max, this is a very distinct data. While VO2max is only calculated by devices, the SpO2 is well and truly measured. It is in fact the pulsating oxygen saturation in the blood, data that will allow you to measure the level of oxygen circulating in your blood and thus detect possible oxygen deficiencies.

Once again, SpO2 is available on the new Apple Watch Series 6, but this measurement is also found on the Withings ScanWatch or the Samsung Galaxy Watch 3. To make this measurement, these watches use a similar system close to that of medical equipment, a small cap in which you will place your finger and which, thanks to pulsed light, will be able to measure reflected light and absorbed light based on the oxygen level in the blood. On connected watches and bracelets, it is therefore the same system which is deported this time to the wrist. Note that here we have a system quite similar to that of the heart rate. However, this time it is a red light, and not green.

The very role of the blood is to transport oxygen throughout the body, we consider that a normal saturation is 95 at 100 %. Under 95 %, we can start to worry about a lack of oxygenation. Usually, this measurement is to be related to the VO2max, since a low volume of assimilated oxygen can explain a low level of oxygen in the blood.

Concretely, the measurement of SpO2 can be interesting for athletes at altitude, or for people with breathing difficulties. As part of the Covid-19, one of the symptoms of the virus was found to be a low level of oxygen in the blood.

One of the latest innovations introduced in recent years on a few connected watches is the electrocardiogram (ECG). This is actually an even more accurate data than just the heart rate, since it is a graphical visualization of the electrical signals of the heart, in the form of a curve.

We will find this measurement on a handful of devices only. It must be said that unlike the heart rate monitor, the electrocardiogram is a medical device. To be able to offer it to their users, manufacturers must therefore have their connected watches certified by health authorities, whether it is the FDA in the United States or the European Commission for France. This has been the case with Apple since the Apple Watch Series 4, but also from Withings with the ScanWatch or from Samsung with the Galaxy Watch Active 2. However, not all countries are housed in the same boat and the ECG function of some watches may only be available in certain countries. This is the case for example with the Galaxy Watch Active 2 who benefits from the EKG in South Korea, but still not in France.

Concretely, to suggest an electrocardiogram, connected watches will send a weak electrical signal through the user's body which will pass through the wrist where the watch is attached and a second point. It is therefore necessary for users to touch a certain place on the watch - for example the crown on Apple Watches - and to wait for about 30 seconds.

You can then discover the electrical signal curve of your heart., corresponding to his activity. The main interest of the electrocardiogram, particularly in general public use, is to detect any atrial fibrillations. In other words, the ECG will allow you to see if your heart has missed one or more beats, if it beats too slowly, too fast or irregularly.

Unlike other data which mainly responds to sports use, the electrocardiogram is therefore a real health device. It will therefore allow you to notify your doctor in the event of a heart problem so that you can consult and be offered medical treatment.. However, since the ECG requires you to put your hand on your watch, the function cannot be permanently activated, or randomly. It is therefore up to the user to regularly use the feature to discover a potential cardiac arrhythmia.

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Smartwatch, Heart rate, Electrocardiography

World news – FR – Heartbeat, VO2max, SpO2, ECG : how smartwatches take care of your heart

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