Tracker & Cell Phone:

A Match Made in Heaven... Or Is It?

Fitness trackers are ubiquitous and one might say taken for granted, but if you think of all the sensors they are packed with and the technology that stands behind them, it is impressive what these tiny bits of plastic and rubber are capable of in combination with a smartphone. To give you a better understanding of what exactly happens on your wrist, we took apart all the technologies involved in the functioning of the majority of fitness trackers.

How They Know You Are Moving

The idea of counting steps is, in fact, very old. In spite of the lack of documented sources, there is general agreement that as far back as in the 15th century Leonardo Da Vinci invented a device that would count steps warriors took during their military campaigns, information that could later be used for making more accurate maps. There is very little proof out there for any of the speculations made about the history of pedometers, but it is established as a fact that the 18th century saw Swiss watchmaker Abraham-Louis Perrelet devise a mechanism that would rewind the wristwatch from the motion of its wearer, which seems like an obvious forebearer of the modern pedometer. It was not until the 1960s, however, that pedometer as a tool for achieving fitness and health was first widely marketed in Japan and this was when the ubiquitous 10,000 steps a day came into play. The pedometer was called manpo-kei, which is Japanese for “10,000 steps meter”, and became strikingly popular in the wake of the 1964 Olympics held in Tokyo.

Clearly, those first pedometers were rather crude and it is not their miniature versions that we have in our modern-day trackers. The technology for measuring motion that hides inside our FitBits and AppleWatches is a 3-axis accelerometer that you could call a descendant of Da Vinci’s pendulum-type pedometer. It was first used by NASA during the Space Race on their lunar modules and was actually significantly more elaborate than what our phones and wearables are outfitted with. A simpler version was adopted for commercial use in car crash testing and airbag design, which was eventually picked up by phone manufacturers in 2000s.

How They Know Which Way You Are Moving

It is a gyroscope that gives your tracker its ability to measure rotation and orientation in space. A great number of minds were involved in eventually making gyroscopes what they are now. It all started in the 19th century with a rather sizeable device that was used for demonstrating the rotation of the Earth on its own axis. In the early 20th century it was adopted for use in the military for improved naval navigation and later in aircraft and missile navigation systems. Gyroscopes were later miniaturized and made accessible through the usage of MEMS technology (microelectronics) and it is due to this that your tracker knows the direction of your motion.

What About The Floors You Have Climbed

Some devices have an altimeter for measuring your altitude, something that can come in handy if you want to know how many flights of stairs you’ve climbed in a day, how intense your walk up and down the hills of San Francisco was or how high your climbed on that last hiking trip your took. Altimeters are no different from most modern-day technologies in that they were also developed for military use and later on commercial planes.

How They Know So Much About Your Heart

One of the seemingly most enigmatic features trackers have these days is heart rate measurement, which is achieved in two different ways. Most trackers have an optical sensor that illuminates the capillaries in your skin and measures the amount of light either reflected or absorbed, which differs with the changes of blood volume during the cardiac cycle. This method is called photoplethysmography (PPG) and was first used and in fact still is widely applied in medicine to gauge cardiac activity.

A different method, used, for instance, in Jawbone UP3, is bioimpedance, the measurement of skin’s electrical conductivity, also known as galvanic skin response, or GSR. Even though this abbreviation may not ring any bells with you, we are all familiar with GSR from lie detectors or polygraphy. Think of how you often see patients in hospitals with a clip attached to one of their fingers - that’s also measuring GSR.

What Is Still Missing

To make any use of all these different sensors fitness tracker manufacturers develop algorithms to combine all the separate readings and give you the actual heart rate, calories burned, steps taken, miles covered, stairs climbed and hours slept.

Now let’s recap... there are sensors to take all possible readings and there are algorithms to turn them into some real numbers. Although it may seem perfect, there is still no way for you to know what those numbers mean on a deeper level and what all those readings add up to on a long-term scale and whether you should be worried about something and go see a doctor.

One might say that creation of fitness trackers was a fit of taking technologies used for any number of non-commercial purposes and making them accessible to the public. What still seems to be missing from this not-yet-perfect circle of creation is depth and real value, which could, in fact, be achieved simply by adding a dab of medical insight and expertise into this medley of data.

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