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How Do Fitness and Activity Trackers Work?

Owning an activity fitness tracker can do wonders to motivate someone into moving and sweating, but we all know that these trackers are not magical products conjured by wizards. They are powered by science, and knowing at least the general idea of what that science is would help us understand how we should treat the information our trackers show us.

The Structure of a Tracker

Generally, trackers have a five-layer structure responsible for its several functions. First of these is the sensing layer, the part that contains all of the sensors that measure various body statistics. Next is the MAC layer which takes care of monitoring and controlling the device, as well as power management. Third, is the network layer, responsible for transmission, routing and addressing of data. The processing and storage layer receives and analyzes data from the sensing layer; it also takes care of security control. Last is the service layer which supplies the data to mobile applications or other monitoring software.

The most important of these layers is the sensing layer, for, without it, the tracker would not be able to track anything. The trackers in the market have varying numbers of sensors, a tracker with more sensors is generally considered more accurate. These sensors are the very foundation of fitness trackers, and each tracker fulfills a specific purpose. Let’s talk about basic tracker functions and how their sensors work their magic.

Step Counting

How Do Fitness and Activity Trackers Work - Step Counting

Step counting is probably the most basic of all tracker functions; even a simple pedometer can do this. It performs this function using an accelerometer, a device that measures the intensity and direction of movement. A typical accelerometer consists of two electrically charged plates and a small counterbalance in between. The counterbalance moves from one plate to another when the target moves and a sensor records the motion.

As stated earlier, a simple pedometer can do this, but what sets a fitness tracker apart is its ability to track movement in three dimensions. Pedometers can only record forward-backward motion (axis X), while fitness trackers can also record movement from left to right (axis Y), and up and down (axis Z).

A tracker can differentiate between activities by detecting motion patterns, for example walking would trigger a sizable pulse in axis Z (up and down) while cycling would show little of this but would generate a boost in axis X (forward-backward). The tracker can use the pulses and ticks in the axes to deduce step count, and from there, conclusions about other bodily functions can also be made.

Some trackers contain other devices to even go beyond counting steps. A gyroscope can be used to pinpoint orientation and rotation. An altimeter can be used to measure altitude, which is useful for mountain climbers and those who want to know how many flights of stairs they’ve climbed. GPS can also be used to track distance for cyclists (and also for a more accurate step count).

Calorie Counting

To calculate calorie burn, trackers use data about your heart rate, perspiration levels, and step count. Humans have a basal metabolic rate (BMR), the total amount of calories burned by the body in just doing its fundamental tasks, like breathing and sleeping. A tracker can estimate this BMR using a formula based on the Harris-Benedict equation.

This formula includes variables like height, weight, gender, and age. The BMR is the number of calories your body burns regularly, so if you want to lose weight you have to exceed your BMR. That is why the calorie total on your tracker only records the calories you burn aside from your BMR. The calorie total on your tracker shows how much effort you’re actually exerting in addition to the work that your body does regularly.

Some trackers can take the action you’re doing into consideration when calculating calorie burn. Different formulas can be applied to swimming, cycling and running since these activities all have different calorie burn rates.

There are also trackers which incorporate additional measurements to make the calorie count more accurate. Thermometers can be used to gauge activity intensity (assuming that the skin grows warmer as the workout becomes more intense), which can be correlated to greater calorie burn. Altimeters are also used to take note of steps being climbed and the impact of that on the calorie count.

Sleep Tracking

How Do Fitness and Activity Trackers Work - Sleep Tracking

In sleep centers, a polysomnogram is used to track sleep levels. This advanced machine takes note of brain activity, eye movement, muscle movement and heart rhythm to determine sleep quality.

A fitness tracker cannot employ all of these measures, and but can still track body movement through a process called actigraphy. Assuming that the less you move at night, the deeper your sleep is trackers, attempt to measure sleep levels. Wrist movements are also translated into sleep patterns. Though the methods used by trackers in tracking sleep levels are still debatable, experts still agree that being aware of at least basic sleep statistics would help people in making informed choices about their health.

Fancy Sensors

Certain trackers use more advanced sensors to record more data. Bioimpedance sensors send a tiny electric current to measure the skin’s resistance. This is used to check heart beats per minute. Bands that use photoplethysmography shine light on capillaries to measure the rate at which blood is pumped.  A Galvanic Skin Response sensor (a device made from two electrodes) is also present in some bands. This allows them to also measure perspiration levels.

Activity trackers become fancier and fancier as time passes, and makers promise that they also become more and more accurate as new functions are added. However, at the end of the day, they are still just a collection of sensors that do not have any real impact on your health unless you let them. So use your fitness trackers wisely and take the data seriously. Set goals and always try to reach or surpass them. Science is doing its best to help you keep in shape, so work hard to do your part.

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