Fitness trackers also called health monitors, are electronic devices or software for tracking and monitoring physical fitness-related metrics like speed, distance, calories burned, blood oxygen level, and heart rate.
It is actually a form of wearable computer attached to the body. Read this article to know how does a fitness tracker work.
The first fitness tracker was initially invented by Tony Buzan, a British athlete, to measure and keep track of his training sessions during the preparation for an event.
Since then, fitness trackers have evolved to become more advanced, with many manufacturers using various technologies to monitor the wearer’s performance and physical metrics.
Smartphones and fitness trackers are commonly used together. Smartphones use their apps to access the detailed information relayed by the fitness tracker worn on the body.
Most smartphone apps can automatically download the relevant data from the fitness tracker and transfer it to the smartphone.
The Fitbit Fortius, for instance, can communicate directly with the Fitbit platform and display all the collected data, such as the distance covered, calories burned, heart rate, speed, etc.
Although the Fitbit platform can be used on the Fitbit smartphone, this application has been limited to the iPhone for the time being.
How do fitness trackers track sleep?
Most fitness trackers utilize the accelerometer that comes with it. This feature can detect the movement of the user and assess whether the person is asleep or awake within a given period of time.
In general, most of the available fitness trackers on the market leverage a technique known as actigraphy. Actigraphy is a method that allows measuring the gross motor activity of a person which aids to monitor rest and activity cycle.
To increase accuracy and precise calculation of sleep duration, some of these trackers consider a number of other factors as well.
The in-built microphone on the tracker may detect the ambient noise of the environment that the user is in. Low noise or silence is an indication that the person is likely to be in a sleep-friendly environment.
Other key factors are namely, heart rate and body temperature of the user. It is obvious that the heart rate would be much lower when someone is asleep.
The temperature of the room is also taken into consideration as people cannot sleep properly above 60 degrees Fahrenheit therefore someone in such an environment is less likely to be sleeping.
How do fitness trackers measure heart rate?
It’s always fun peeking into the smartphone screen to see the heart rate after an intense workout session, I bet most of us do it!
So, how does the tracker measure our heart rate, and is it even accurate? Well, there’s this technology known as PPG (photoplethysmography) used by almost every fitness tracker manufacturers including Apple.
Few other makers such as Fitbit call their one Purepulse though it’s based on the same tech as PPG. The secret lies in the fact that our blood being red in color reflects red and absorbs all other colors.
Underneath your smartwatch, you can see green lights being emitted. During heavy activities, heart rate rises meaning more blood flow to the veins under the skin. This results in more absorption of green light by the excessive blood going there.
The trackers detect how much green light is being absorbed by blood which corresponds to the intensity of physical activity i.e heart rate. On the downside, people having tattoos over their skin may not get the precise reading due to hindering the path of light.
How do fitness trackers measure calories burned
Studies indicate that most fitness trackers can’t accurately measure the calories burned, yet somehow approximate value can be extracted. In general, they need some specific personal information of the users like age, weight, height, gender.
These data are then combined and processed by their secret algorithm which varies from manufacturers both in terms of trackers and apps.
Firstly, the users need to input the data of the metrics into the app. The app then calculates the BMR (basal metabolic rate) from these data.
If you didn’t know what BMR is, it’s simply the calories you burn while you rest. The BMR accounts for half the calories a person burns a whole day.
The rest of the task is processed throughout the day when other factors like heart rate, walking/running, sleep are detected by the sensors in the fitness trackers.
All these data are evaluated to give out an approximate if not the accurate value of calories burned.
How do fitness trackers measure blood pressure?
This particular feature that comes with a fitness tracker is beneficial to many who are concerned about their health. People having heart problems must have to keep an eye on their blood pressure because they need to detect heart conditions beforehand.
So how reliable are these trackers in measuring blood pressure?
While at rest, the trackers can actually show more accurate values, but during and after heavy physical activity, the accuracy somehow decreases.
This is why the American Heart Association urges people with serious heart issues to use a sphygmomanometer instead of these wearable fitness trackers.
Most wearable fitness trackers combinedly use PPG and EKG (electrocardiogram). The former measures the heart rate while the latter tracks blood flow. These along with other BMR data, the app uses complex algorithms to show a result.
How can fitness trackers check blood oxygen?
Fitness trackers and smartwatches that have the feature of checking blood oxygen can do so using a SpO2 tech known as reflectance pulse oximetry.
In this method, the infrared and red light emitted from the tracker is reflected by the tissues underneath the skin and the bones. The absorption of light is different in oxygen-rich blood and blood that is deficient in oxygen.
The difference or change in light emitted and absorbed helps the tracker to determine the level of oxygen in the blood.
Though it kind of works, but the reflectance oximetry method mentioned above is less reliable than the traditional transmissive method.
Nevertheless, these ways of checking blood oxygen levels are not recommended over the conventional clinical methods used by hospitals and doctors. The value that these gadgets show is not medically certified to be used or assessed for a diagnosis of patients.
A value above 95% oxygen saturation level is considered to be normal for healthy individuals, anything below 92% calls for attention to find out possible health issues.
People who suffer from sleep apnea can greatly benefit from this feature. If you haven’t known what sleep apnea is, it is a serious case where people stop breathing for short intervals during sleep. This results in snoring and uncomfortable sleep throughout the night.
How do fitness trackers calculate distance walked
A fitness tracker consistently uses the 3 axis accelerometer to assess every movement of the user. Given that it has gathered enough data about the person, it can detect when the person is at rest, moving, exercising, sleeping and whatnot.
In terms of counting steps, none of the fitness trackers are precise to the point you can believe in the number! Most of the time they undercount or overcount your steps.
The gyroscope that comes with fitness trackers can detect the direction of motion and circular motions as well. The walking mechanism of the human body is such that it tilts when we put a leg forward for the next step.
Each stride has a consistent length which the app on the trackers asks you to input when you first set up the device for personalized usage.
The movement of the body is sensed using the tilting mechanism and counted as steps, which is then multiplied by the length of the stride.
The more sophisticated algorithm in advanced trackers uses a combination of much more data than merely these. Nonetheless, we all rely on the numbers that our fitness trackers show when we are out jogging or taking a walk from home to any destination.
On the other hand, most smartphones with GPS can also track distance moved from point A to point B.
How does fitness trackers measure blood sugar level?
This particular feature is undoubtedly beneficial to people with diabetes. Fitness trackers that come with CGM (Continuous Glucose Monitor) can measure blood sugar levels.
Though like other data it can track and measure, blood sugar level is still not a widely offered feature yet as more research and work is going on to make it viable.
Not many people let alone diabetic patients would be happily relying on a device that’s not specifically designed for sugar level detection.
Commonly, smartphones from Apple, Samsung, Fitbit all support CGM devices. Conventionally, the medical practice was to draw blood from the patients to examine blood samples but using fitness trackers with CGM doesn’t involve such actions.
Another limitation of using a smart tracker is that it only detects sugar levels from subcutaneous samples. Usually, the actual sugar level in blood takes time to reach the skin, which may not give the value which the users are actually looking for.
Big manufacturers like Novartis and Google are continually working and testing various prototypes which could be a viable option for those looking for instant diabetic tests without going over to clinics.