Tiny Accessory, Big Brain

You see someone with an almost boxy shaped bracelet on their wrist, what would you call it? A tracker, a pedometer, a watch? My guess is that you would most likely call it a Fitbit. Fitbit has become the eponym of step trackers around the world. If you don’t know what a Fitbit is, it is a “new device that contains a 3D motion sensor that accurately tracks your calories burned-steps taken-distance traveled and sleep quality.” There are many brands fighting to be worn on you wrist but Fitbit is the most well known. The Today Show tested out the most popular fitness trackers (Fitbit, Garmin, and Jawbone), and Fitbit was the most successful in tracking steps. How is this possible if the Fitbit is only 5.5”-8.9” in length and the smallest width is .44”?

Well, it all starts with Fitbit’s 3-axis accelerometer (keep this in mind because it will be brought up later on). An accelerometer is a little gizmo that measures forces. The forces can be something like the force of gravity, or a physical movement force. Accelerometers track the forces that cause your Fitbit to move or vibrate. And because it is a 3 axis accelerometer instead of your average single-axis pedometer your Fitbit is far more precise in activity and measurements. These measurements, of course, are your movements and from the measurements on the accelerometer your Fitbit notes the frequency, duration, intensity, and distance of each measurement/movement. Each movement you take is put into an algorithm to determine if the movement has met a required intensity to be considered a step. If you don’t know what an algorithm is it is a “small procedure that solves a recurrent problem.” In this specific case the problem is if the intensity of a movement is equivalent or even superior to the intensity of a step. Then all of the steps and information that was put onto your Fitbit that day will be transferred over to your phone/the Fitbit app.

a diagram of an accelerometer measuring movement

A Fitbit is virtually useless without downloading the app. When you first log into the app you log your gender, height and weight. By logging in your gender and height, the app is able to estimate two sizes of stride lengths, the walking stride length and the running stride length. With this information Fitbit multiplies “your walking steps by your walking stride length…” and then multiplies “your running steps by your running stride length.” This multiplication process is used to determine the distance of your run and/or walk. These mathematical equations are only used if you do not use the GPS tracker on your device though. When you track your distance through GPS it is connected through your phone and “if you begin moving before you get a GPS signal, the tracker will calculate distance using steps and stride length…until a GPS signal is found” (Fitbit).

Your Fitbit can figure out how many calories were burned during your movements as well. Based on the data that you physically logged into the app (weight, gender, age, and height) and the exercise/movements you have made that day how Fitbit assumes your BMR. Your BMR is your basal metabolic heart rate, this means that it is an estimate of how many calories you’d burn if you were to do nothing but rest for 24 hours. It represents the minimum amount of energy needed to keep your body functioning, including breathing and keeping your heart beating.”

Fitbit even measures the movements in your sleep to determine your sleep quality for each night. Usually in a sleep study researchers use polysomnography. In a typical sleep study researchers record “your brain waves, the oxygen level in your blood, heart rate and breathing, as well as eye and leg movements” while you sleep. Since Fitbit is unable to figure out brain waves, and oxygen levels, it uses the next best thing — actigraphy. Actigraphy is “the continuous measurement of activity or movement with the use of a small device called an actigraph,” so it is far less intrusive than a polysomnography. A Fitbit can be considered an antigraph because an actigraph is “usually a device worn on the wrist that tracks movement while you’re sleeping. Software then translates those movements into periods of sleep and wake.”

Some Fitbits when tapped fast and frequently are put to sleep, and will track your sleep activity from the time of when you put your Fitbit to sleep until the time where the accelerometer measures enough strong and constant movement to assume you’re awake. If you have not moved for an entire hour and not put your Fitbit to sleep, it will assume you are asleep. The only issue, for those couch potatoes who wear their Fitbits, is that if you don’t move for an hour and you are not asleep, you can always go back into your sleep log and change your data. Based on the measurements of your movement from the accelerometer in the Fitbit your sleep cycle can be determined. From the measurements it can be decided when you go from “light sleep to deep sleep, back to light sleep, and then into REM sleep,” which is the most common sleep pattern for the average person (Fitbit).

All this information in such a tiny bracelet, ‘What happens if it is lost?’ you may find yourself asking, ‘If I lose my Fitbit, will I lose my information?’ The answer is no. For such a “tiny bracelet” it has quite the big memory If you have synced your phone with your Fitbit you information will be kept on your phone. Fitbits themselves can only hold up to 7 days of “detailed minute-by-minute data.” But it will keep up to thirty days of summary data. Which means your daily steps, calorie burning, distance, are all kept for thirty days. You won’t be able to see how many steps you took every hour, how many calories you burned every hour, and how many miles you’ve walked every hour after thirty days. Therefore, don’t lose your Fitbit because your summary data is far less detailed than the data that is recorded after 7 days.

So next time you aimlessly pace around your room worrying about the amount of work you have to do, think about all the technology that goes into counting those pointless steps. How many steps did you take? How many calories did you burn? How strong were your movements? Did the Fitbit recognize them as steps? Well when you look on your Fitbit to see the number of steps, number of calories, intensity of your movements, now you know how the little bracelet on your wrist is able to tell you all this otherwise difficult information. But what you choose to do with this data is entirely up to you.