Can fitness trackers be trusted?

Keep­ing your­self in good phys­i­cal shape is nev­er easy. But the mod­ern user has a lit­tle help for this. Fit­ness track­ers and smart­watch­es remind a per­son to move, count steps, mea­sure heart rate, cal­cu­late calo­ries burned and, in gen­er­al, help to mon­i­tor their phys­i­cal activ­i­ty in a famil­iar and under­stand­able dig­i­tal form.

But how accu­rate are these devices? Answer to this ques­tion Dig­i­tal Trends giv­en by Lisa Cad­mus-Bertram, pro­fes­sor of kine­si­ol­o­gy (the sci­ence of mus­cle move­ment) at the Uni­ver­si­ty of Wis­con­sin-Madi­son. “The short answer is dif­fer­ent. Long — fit­ness track­ers are accu­rate enough to be use­ful for most peo­ple in most tasks. But their accu­ra­cy depends on what exact­ly you are try­ing to mea­sure.”says Pro­fes­sor Cad­mus-Bertram.

Almost all fit­ness track­ers count steps and dis­tance trav­eled, many mea­sure heart rate. Some mod­els allow you to cal­cu­late the num­ber of calo­ries burned and mon­i­tor sleep. By the way, many smart watch­es also have such func­tions. Let’s take them in order.

Step counting

The sim­plest task for a fit­ness track­er is to count the user’s steps. There is a pop­u­lar the­o­ry that for opti­mal phys­i­cal fit­ness you need to walk 10 thou­sand steps a day. Users who try to fol­low this norm try to keep count with smart bracelets. Unfor­tu­nate­ly, they do not always show the truth.

“Step count­ing is gen­er­al­ly pret­ty accu­rate. But there are a cou­ple of excep­tions — peo­ple who move too slow­ly or have a non-stan­dard gait may notice that their steps are not count­ed by the device”, says Pro­fes­sor Cad­mus-Bertram. Accord­ing to her, if you put on a cou­ple of dif­fer­ent fit­ness track­ers and acti­vate a pedome­ter on your smart­phone, then all three devices will show dif­fer­ent results. And the smart­phone in your pants pock­et will be the most accu­rate. This is because the devices on the user’s leg count the steps best.

“The hip is the best place to mea­sure steps and most types of phys­i­cal activ­i­ty. A smart­phone in your pants pock­et needs to cal­cu­late your steps very accu­rate­ly.”says Cad­mus-Bertram.

Alas, despite the accu­ra­cy, a smart­phone in a jeans pock­et is not very suit­able for sports — it sim­ply gets in the way. A smart bracelet on the wrist will inevitably record unnec­es­sary move­ments, but from the point of view of com­fort of use, it is the best option. In addi­tion, plac­ing the gad­get on the arm allows you to use oth­er sen­sors in addi­tion to the pedome­ter, such as a heart rate sen­sor. This gives a more com­plete pic­ture, but there are nuances here.

Heart rate measurement

“Devices that mea­sure heart rate can be quite accu­rate when it comes to rest­ing mea­sure­ments. But they show a very incon­sis­tent result dur­ing phys­i­cal activ­i­ty.”says Cad­mus-Bertram.

When you exer­cise, the track­er read­ings can devi­ate great­ly from real­i­ty. On sweaty skin, the sen­sor may miss shocks, show­ing an inac­cu­rate result. This also applies to smart watch­es — the more intense the phys­i­cal activ­i­ty, the less accu­rate the mea­sure­ments. Accord­ing to Pro­fes­sor Cad­mus-Bertram, at any giv­en moment, read­ings can devi­ate by 20 beats up or down. How­ev­er, with suf­fi­cient­ly long mea­sure­ments, the aver­age result will be close to real­i­ty.

In gen­er­al, the accu­ra­cy of a fit­ness track­er or smart watch depends on what the mea­sure­ments are for. Even the lat­est Apple Watch with its new sen­sor can­not match the qual­i­ty of mea­sure­ments with a full-fledged elec­tro­car­dio­gram made on pro­fes­sion­al equip­ment. But still, the watch is able to catch signs of a poten­tial prob­lem and rec­om­mend the user to see a doc­tor.

In gen­er­al, if you’re run­ning a marathon and want to keep track of your heart rate, a fit­ness track­er won’t help you. In this case, it is bet­ter to use more pro­fes­sion­al heart rate belts attached to the chest.

Counting Calories Burned

When it comes to count­ing calo­ries burned, the result is extreme­ly dif­fi­cult to eval­u­ate. Typ­i­cal­ly, fit­ness track­ers with this fea­ture mea­sure phys­i­cal activ­i­ty and com­bine this infor­ma­tion with the user’s height, weight, gen­der, and age. Some­times track­ers offer the host to answer a few ques­tions about their lifestyle. In any case, the result is very approx­i­mate.

“The prob­lem is that the track­er can’t know cer­tain things about your body. For exam­ple, it only assumes the ratio of fat to mus­cle in the body, although this para­me­ter direct­ly affects ener­gy expen­di­ture”explains Cad­mus-Bertram.

Recent jour­nal research Sports Med­i­cine con­firmed that all exist­ing fit­ness track­ers give very inac­cu­rate results, espe­cial­ly when it comes to slow activ­i­ty, like nor­mal walk­ing. How­ev­er, they can still be used as a use­ful tool. Accord­ing to Cad­mus-Bertram, this requires the track­er to be cal­i­brat­ed.

For cal­i­bra­tion, the pro­fes­sor rec­om­mends wear­ing the track­er for a month, and at the same time enter­ing data on every­thing you eat into it. By know­ing how many calo­ries you’re con­sum­ing and how many you’re los­ing, you can cor­re­late that infor­ma­tion with changes in your body weight and cal­cu­late how wrong the track­er is. Know­ing this error, in the future the device can be used for its intend­ed pur­pose.

Also, do not for­get about the sim­ple psy­cho­log­i­cal effect. When you see a visu­al result in the form of num­bers, you begin to work on your­self a lit­tle more active­ly.

How to choose a fitness tracker?

First of all, you need to pay atten­tion to com­pat­i­bil­i­ty with a smart­phone. If you have an iPhone, it makes sense instead of a sim­ple track­er to buy an Apple Watch that has all of these fea­tures. But with an Android smart­phone, the choice becomes more diverse.

Even if you buy a cheap track­er, it is worth stop­ping at mod­els with a heart rate sen­sor. This sen­sor may not be very accu­rate as a heart rate mon­i­tor, but its pres­ence real­ly affects the oper­a­tion of the pedome­ter. As tests show, track­ers that simul­ta­ne­ous­ly ana­lyze infor­ma­tion from the accelerom­e­ter and heart rate sen­sor pro­vide more accu­rate data on the user’s phys­i­cal activ­i­ty.

Pro­fes­sor Cad­mus-Bertram does not rec­om­mend spend­ing too much mon­ey on a track­er. “I would rec­om­mend stick­ing with the cheap­est mod­el that has a heart rate sen­sor. Of course, you can pay twice as much, but you will not get any sig­nif­i­cant addi­tion­al fea­tures”she says.