An inside look: physical activity tracking

A source

Scientists have one small weakness - to set up experiments and analyze the results. I set a couple of experiments dedicated to monitoring physical activity for 24 hours. Details, measurement technique, comparison of the results of the number of heartbeats are presented under the cut for two days with low and high levels of physical activity.

opening speech

Fitness tracker in my life appeared relatively long ago - almost two years ago. It was an ordinary bracelet, which counted the number of steps, then a chest strap for measuring the pulse was already purchased. At that time, it seemed that one had only to start wearing this miracle of scientific and engineering thought, follow the advice of a soulless program on the phone, which impartially monitors physical activity and the highway to healthy life is open. However, life has put everything in its place.

Even on Habré and GT there are a lot of articles devoted to a bright future of telemedicine and "cloud" doctors , who can do that and make a diagnosis according to "human telemetry". There are even reports that fitness trackers can save a person’s life by recognizing any heart disease or can determine the source of an earthquake better than the geological service.
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On the other hand, doctors still do not know or are “not sure” of the applicability of data from fitness trackers for a “personalized” approach to medicine. Where to store this amount of information? Fitness tracker measures pulse every 5 seconds, giving out more than 10,000! points per day, it is about 0.5 MB in a two-column CSV, 200 MB per year. But you also want to accumulate statistics, see the dynamics in the context of 5-10 years. How to handle? Over 300,000! points per month, not every program for plotting such a master. And most importantly, why?

There you can add some more questions: to what extent are the data obtained by recurrent fitness trackers? What is the error and probability of error?

In general, it turns out that there are more questions than answers, so below I will describe a full-scale experiment and summarize some obvious and not very good results. I will also try to answer the question: who are they, fitness trackers - a useless toy or a valuable tool that allows you to collect a huge array of data for personalized medicine?

Types of heart rate monitors

Today, there are two fundamentally different schemes for measuring heart rate or heart rate (HR), or HR for short (heart rate).

The first and most popular of them, perhaps, is the green laser. From the manufacturer to the manufacturer and from model to model, only the position of the sensor and the number of LED lasers around it change.

The principle of operation is simple. In the blood there is heme (hemoglobin), which dyes the blood in a bright red color, this hem intensively absorbs in the green part of the spectrum. The blood, even in the smallest vessels, pulses with the same frequency as the heart, which provides blood flow. We direct the laser to the skin and measure the pulsation of the reflected green light, from where we calculate the pulse.


The principle of operation of the laser heart rate monitor. A source

Another type of heart rate monitor works on the principle of ECG , with the only difference that instead of a dozen electrodes only two are used.

A pair of electrodes is fixed on the chest (as my practice shows, you can not even wet it). The potential difference, which corresponds to heartbeats, is recorded using a separate mini-computer that transmits data to external devices via BlueTooth.

NB: It is interesting that, for example, some simulators support the HR function via the BT channel, so during training the data is automatically displayed on the display. Below is an example of how it looks on Concept 2 rowing machines:


A source

The reader will ask the question, what is better? To give a direct and unequivocal answer is difficult.
If there are no diseases of the cardiovascular system and accurate measurements are needed only during exercise (athletes, for example), then a bunch of just a bracelet and a sensor on the chest would be the best choice. If the task is to monitor the pulse around the clock (for example, due to heart problems), then choose a bracelet with a built-in sensor. Full comparison with the analysis of certain aspects in English is given here .

Literally two words about the reliability of the data. On the same site Wareable.com there is an interesting article dedicated to testing the accuracy of the data obtained by different sensors. It turns out that the laser sensor produces "reproducibility" of about 85% at ± 5 beats / min, while the chest strap allows you to reach 91%.

From myself I’ll add that my heart rate monitor specifically measures the pulse every 5 seconds, that is, if there were 5 beats in 5 seconds, then HR will be calculated as 60 beats / min. In the relaxed position, the hand-measured pulse was 60 beats / min, and the chest strap gave values ​​from 58 to 63 — quite acceptable accuracy.

But back to our sheep ...

Part experimental

To monitor the pulse, I wore a chest heart rate monitor in conjunction with a fitness bracelet for several visits with breaks for recharging and unloading data: working day + evening time at home and separately - night. Bracelet with heart rate monitor are synchronized via Bluetooth.

In order not to spoil and avoid accusations of advertising, I’ll bring specific models here (who needs to open and look).


Next, we will break apart the usual “office” day (thanks to the thesis, there were quite a few of them) and compare it with the day when we had to endure much of the time “on our feet” (she works in the laboratory). As a bonus to this article there will be pulsograms from a gym workout and a mountain hike.

Office Day

In order not to torment, I will immediately give the general picture, which is presented in the figure below. In fact, this is a 24-hour pulsogram of a typical “office hamster”.

Looking ahead, I will say that any physical activity has a long trace of “relaxation” when the pulse returns to “normal” for 30–40 minutes. A "rise" of the pulse around 9-30 and 12-00 is two cups of coffee.

But let's take a closer look at it ...

We'll start with a wake of about 7-30 and a race to the train, where I usually get to work. After waking up, the pulse jumps from 60 (so to speak healthy sleep) to 80-90 beats / min (charges and moving around the house). Then a light jog to the train and the pulse goes above 120 beats / min. Then the rest time in the train, 40 minutes - nothing happens and the pulse returns to 80 beats (work on the computer, view the news on the phone). And, of course, the arrival and walk to work is relatively calm step, and all the bursts - staircases.

Next, the first half third of the working day and lunch, the pulse in a calm state is between 70 and 80 beats / min. Trends for tea / coffee and to the printer look like short-term bursts of up to 90-100 beats / min. At about 11:30 am to 12:00 pm, lunch time comes and the pulse rises slightly to 90.

The second half of the working day - without changes, around 70-80, periodically the bracelet reminds that it is time to show some physical activity - you have to obey the mindless piece of iron on your wrist and walk around the office.

The end of the working day. It is necessary to get to the train, the pulse jumps again to 90-100 beats / min (I usually leave at the very last moment). And again, 40 minutes of sitting mode. Then a long and long climb to the mountain, dinner and some household chores.

The most interesting thing happens at night. As you can see in the graph below, at night the pulse remains relatively stable - 60 beats / min, sometimes jumping up to 70. But on the pulsogram, “spikes” are clearly visible - a sharp but not prolonged increase in the pulse. On these spikes, one can actually track the activity of a person during the nighttime and predict when it is easiest to wake him up. It is on this principle that work: a) wristbands with wake-up function and b) sleep applications.



We have analyzed the main stages of the “office hamster” day cycle, now let's turn to the cycle of an employee who spends most of his time on his feet, in movement and work with his hands.

Laboratory Day

It is clear that at night there will be no cardinal differences, but during the day everything is completely different. Due to the fact that you constantly have to move, do something with your hands, walk from one room to another, the average pulse is 10-15-20 beats / min higher than with a sedentary lifestyle.

To make it a little more visual, let's build both graphs in the same coordinates:


The same graph, if you add averaging

The main conclusion, the most obvious, of course: move more at work, even if the work is sedentary, then you just have to come up with a lesson that will make you walk every hour or one and a half.

Oh, sport, you are the world!

The first thing I want to tell you about is, of course, rocking or fitness - as you like. The pulsogram below shows my typical workout for about 1.5 hours. In the beginning - a warm-up, some simple exercises that help bring the muscles into a tone, then a rowing machine to get warm, a little rest, and about 30-40 minutes of standard exercises with free weights and / or other simulators.

It is worth noting that this particular training "consumes" about 1050 kcal, which is equivalent to approximately only 2-3 Snickers 50 grams. Here you can write a whole treatise on heart rate zones and so on, but I will not, just leave a screenshot from the program.



We also love to go to the mountains with friends and colleagues, so the pulsogram and a map of one of these trips are presented below. Interestingly, a constant rise up raises the lower bar of the pulse to about 95-100 beats / min, and the average heart rate for the entire route is about 125 beats / min, which is very good for burning extra calories.


Pulsogram at mountain hike. Easily guessed lunch and photo-halt


Map, speed and elevation for clarity. For some reason, the height scale is not displayed: the maximum mark was 2380 m, the minimum - 1130m


And a small sammari

Conclusion and conclusions

First , you need to move more and more often, no matter how trite it sounds. Many need a weighty argument to begin to engage in themselves, go to the gym, relax in nature and just move more. I hope that in this article I was able to clearly demonstrate that even an ordinary walk around the office for a glass of water or a cup of coffee makes the heart beat faster by at least a third more 20-30-40 minutes after returning to a comfortable chair. The more and more often it is reduced, the more calories are burned in the body.

Secondly , a person of modern "sugar" civilization consumes too many calories from food. Hence, the legs grow in a variety of problems: from diabetes to heart disease. At the same time, it is almost impossible to refuse products with a sugar content even at 10–15 g per 100 g (read the fine print on packages). There is only one way out - to burn calories yourself. In my opinion, the insane inscription on the wrist - “it's time to move!” - is an excellent occasion to once again recall the food eaten for all snacks during the day and go to the fitness center.


Thirdly , a fitness tracker with the ability to measure heart rate is a great tool for doctors to monitor patient health and predict "problem" events. To date, the main difficulty lies in how to accumulate and process such a data array automatically, giving the doctor only a squeeze / prediagnosis.

Fourth , unfortunately, security problems are the flip side of the advantages of fitness trackers. In fact, as I showed in the article on the pulsogram, you can track a lot of information about a person: the duration and nature of sleep, daily routine, work style ("office hamster" and the person "in the fields") and much more. In fact, it is a hidden spy agent on the wrist.

But back to the question posed at the beginning of the article: so who are they fitness trackers? In my opinion, fitness trackers are definitely a useful tool for monitoring your if not health, then daily activity, which indirectly affects health. If they were able to collect data on blood sugar and oxygen levels, they would become an indispensable “horse” of personalized medicine and sporting achievements.

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