How to extract maximum value from fitness trackers despite inaccuracy

Once upon a time, a humble pedometer underwent a transformation. These days, wearable technology market offers gadgets of all shapes and sizes and keeps evolving at a rapid speed. Or so it seems. More fitness trackers than ever are collecting dust in their owners’ drawers, abandoned for broken promises of leaner, healthier body and never-ceasing motivation. But before condemning them useless, consider your demands are you simply asking the wrong questions?

When Polar has filed its patent for the first wireless, portable heart rate monitor in 1980, it was a significant breakthrough. But 1980 wasn’t the year heart rate training was born – trainers and sports researches relied on the manual way: a pen, a pencil, a stopwatch and a finger on the vein. Early mornings, before they rolled out of bed, athletes all over the world were counting their heartbeats while staring at the seconds hand of a plain wristwatch or an alarm clock, then logging their resting heart rate down. Fluctuations in numbers provided crucial data: resting heart rate is a key metric for recognising how much strain the body could take. Their coach would have a hawk’s eye on it – to manage optimal training load and prevent overtraining.

Technological advances make data collection a breather. No more pen and paper, no more forgetting to log your exact go-to-bed and wake up times. Technologically, we have never been at better times to improve our health, drive our performance and prevent injuries. Yet, there is a significant problem: a lack of education on what to do with the data collected.

In this article, you will learn how to use trackers to their maximum capabilities and how to select the ones that will serve you longest.

24/7 Fitness Trackers

There are many curious trinkets designed to make your life better. Fitness trackers are the Jack of all trades among wearable tech. They can provide plentiful stats on sleep, heart rate, activity levels and, sometimes, even recovery. A single tracker that suits your needs can cover all your data collection bases. However, there are a few things to consider:


No other topic has sparked more controversy than the accuracy of a given tracker. It doesn’t help that manufacturing companies keep throwing marketing claims that sound like a creative variation of “the most accurate tracker”. You may be already familiar with fire-blazing debates on how much error is acceptable. And some individuals are rock-solid that if the data is not accurate, it’s useless.

I don’t believe that inaccurate data is useless. The old-school tracking methods of paper, pen and a stopwatch all have a significant margin of error, especially during high-intensity exercise when the heart rate is high. They were used because they were accessible and because deciding based on this data was better than deciding based on nothing. Moreover, the same human tends to be more or less consistent with the way they measure. Similarly, the same device has its own tracking patterns – it is the dynamics that provide most insight, not the one-off numbers.

Let’s take a closer look at the factors that influence both the quality and consistency of the measurements:


This refers to the quality of build and sensors. Medical and research-grade devices boast solid accuracy (but they too have a margin of error) in large due to the quality of parts and construction. And the cost reflects it – it would be prohibitive for the general folk (3000$ tracker, anyone?). The truth is, most trackers you can lay your eyes on have almost identical quality of build, very similar sensors (accelerometres coupled with an optical heart rate sensor), as well as excellent chances to be assembled on the same factory somewhere in Shenzhen. Whatever sweet, sweet marketing songs you may hear, there is no point worrying about hardware.


Once the sensors collected the raw data, it’s the algorithms’ job to translate it into meaningful numbers you can see on the screen or the phone app. Unlike hardware, some companies do have better algorithms than others. However, since all of them are proprietary, patented and otherwise top-secret, it is somewhat difficult to establish whose ones are more accurate. When asked for advice, I suggest looking at trackers produced by companies who cater to athletic clientele rather than non-athletic consumers – Polar, Garmin and the likes. Unlike Fitbits and Apple watches, they have been in the game of sports technology innovation many decades before the competition and had substantial time and research to fine-tune their algorithms.


This is the ultimate point of tracker’s accuracy, which can be identified by anyone. The further away from the centre of the body the tracker is worn, the less accurate it will be, no matter the hardware or algorithms. It’s physiology. No amount of innovation will ever overcome it. The smallest margin of error among portable devices belongs to those worn closest to the heart – yes, chest straps. Then follow the devices worn on the bicep strap. Then, the forearm. Then, the wrist, where the majority of trackers are worn nowadays. Then, finally, the ring-type trackers of all sorts. Just like how doctors suggest to people over a certain age to use an upper-arm-type blood pressure monitor instead of the wrist-type one due to accuracy concerns, the same principle applies for fitness trackers: the further away from the centre of the body, the more unintended movement it will be picking up and the wonkier the heart rate measurements will be.

Wristband trackers still do an acceptable job when you are not exercising. But if you are planning to use them to track your workouts, the best option is to pick the one that can either be paired with a chest strap or can be moved to the upper arm for better accuracy.

Purpose and goal setting

This where the proverbial rubber meets the road, as well as where the good majority are using their trackers wrong. The biggest mistake is treating the numbers displayed as absolute truth – they are not. And it’s OK.

Understanding the limitations of trackers and how you can still use this imperfect data will help you separate the essential from useless, stop wasting money in search for the perfect one and finally get the body, sleep and other things you’ve been promised.

Now, it’s time for a fundamental question:

“What outcome did I hire this techy guy to do for me?”

You paid for it, after all. I bet you had some reasonably detailed ideas about what exactly it should do for you. It may be one thing. It may be a few. This clarity will help you answer the second fundamental question:

“Is the outcome I hired this techy guy for actually happening?”

And, in case it is anything but a resounding “yes”, there is the final one:

“What needs to change?”

Why it is a terrible idea to use fitness trackers for calorie tracking

With the popularity of calorie counting, buying a fitness tracker to advise you on how many heat units you incinerate and compare those against your meticulous MyFitnessPal inventory may seem like a wise idea, except that the number you see on any given tracker is not the number you actually burn in real life.

It may be off by a whopping thousand. Yes, a thousand. Perhaps, more. There are way too many variables in the human body to measure calorie burn with acceptable accuracy without lab settings and a gas mask on your face. Still, there is a way to use the calorie estimation feature to help you with nutrition adjustments:

If you are hitting a consistent amount of calories on your tracker throughout your days (say, around 2000 every day), you will know that you have almost consistent daily activity output.

If you know you have a consistent daily activity output but seem to be getting heavier by scales, wider by tape and fluffier on photos, you can adjust the amount of food you eat and see what happens. If you are lighter by scales, narrower by tape and leaner on photos, you can, likewise, adjust the amount of food to suit your needs. By doing this, you eliminate a major variable (inconsistent activity levels) and reduce the potential problem-solving to the amount of food you eat and how well you sleep. And to do that you don’t even need to count any food calories, you can just eat a little bit more, a little bit less, or the same way, depending on your goals.

I need to move more

Trackers are excellent devices to help you increase your activity levels and even standardise them across your days. For this goal, two metrics can be use

  • Daily Steps
  • Daily Calories

Daily calories estimation is a suitable metric for those who train on a regular basis. Most weight training, naturally, doesn’t involve any steps. You can set yourself a daily calories target, and most devices will display a neat percentage of goal achieved throughout the day. You will likely find yourself standing up from your work desk, trying to sneak some extra activity, as a single gym session will get you puny 30% at best. Maybe, you will even volunteer to wash the dishes in an attempt to nail your very last few percents.

Daily steps is a solid activity metric for those who don’t purposefully exercise yet. Walking is a superb exercise by itself, and an excellent place to start. Just like with daily calories, you can set yourself a daily steps goal. Likewise, you are more likely to take a short walk during your lunch break. And when it gives you a digital pat on the back when you hit that 100 %, it feels incredible! You almost wish humans did that a little more often.

Some trackers will even buzz you when you sit longer than one hour, telling you to stand up and move. My Polar A360 (discontinued, they have A370 now) will go as far as giving me inactivity stamps if I ignore it and choose to remain implanted in my work chair. But I owe it to him, and I didn’t have back pain for a very long while.

I need to know my heart rate during exercise

The two most common ways to measure heart rate during exercise is by using a heart rate transmitter (chest strap) or pulse oximetry (optical sensor). Most of wristband fitness trackers have a built-in optical sensor, but it is unlikely the best option for your needs.

Chest straps, when good quality and properly used, provide nearly ECG-level accuracy. Optical sensors, despite claims by some companies, do not. This is where the question of what is the acceptable accuracy for beginners comes in. After all, recreational exercisers aren’t professional athletes, and less accuracy is fine, right?


It is the beginners and the recreational exercisers that need the best HR accuracy they can get their hands on. Why? The reason is simple: awareness. Most professional athletes and dedicated enthusiasts have developed their body awareness to an extent where they can “feel” their heart rate within 2-3 beats off the actual ECG accuracy. Professional athletes and long-term exercisers can easily tell when the number on their HR monitor is off or when the electrodes on the strap are not wet enough. They will undoubtedly feel it if their heart rate will start creeping up to risky levels, not to mention that their cardiovascular systems are so well-trained that very few things can spike their hearts to the danger zone anyway.

It is not the case for the average population, working seated jobs, driving cars and barely, if ever, training their hearts. They need a reliable heart rate reading to ensure the exercise is safe and to let their trainer adjust the workout intensity properly. With time and accumulated experience, they will also develop the skill to “feel” their heart rate.

Chest straps are not uncomfortable, and no choking deaths were reported, although, admittedly, I only used the ones by Polar. All straps I have are very soft on the skin and get softer with use. A chest strap has a pair of electrodes that need to be wet to conduct electrical impulses and slips comfortably underneath a bra band. You do not feel it during exercise.

Chest straps, despite better positioning, however, are not fail-proof. The hardware matters, the quality of electrodes matters. Also, with the recent swimming-friendly straps, the signal can be impaired due to lack of moisture – tap water just runs off the silicone electrodes. There is a solution: water-based conductive gel, also known as ECG gel. You can get it in sports stores and pharmacies. If you prefer to go old-school or forgot the conductive gel at home, saliva works too.

Optical sensors used in the bicep area can also be a fairly reliable choice. To use them, your device needs either the ability to pair with the external bicep strap or an option to move the device itself to the bicep or the forearm area.

Trackers with only wrist-based optical HR tracking available are not ideal as heart rate indication is often delayed and can be off by ten beats or more. If knowing your heart rate during exercise is the outcome you hired such tracker for, it will not deliver.

I need to sleep better

I haven’t yet met someone who, after a few nights of using a tracker, wouldn’t utter a variation of:

“Whoa! Never thought I sleep so little!”

The time opportunity you give yourself to sleep (which starts from the moment you pull over the blanket and ends with a shrieking alarm clock) does not equal to the time you actually sleep.

The well-known recommendation of about eight nightly hours of zzzz refers to the time you actually sleep. But most people don’t even spend that long in bed, and implications are dire.

If a tracker can trigger such a powerful insight, it has already done half the job. The second half is to make you act, and, ultimately, get the sleep quantity and quality you need. That is, establish a sleep routine that works for you.

Back in the days, the in bed and waking up times were logged manually. Modern trackers eliminate this need – they record this without you needing to press the button. Thanks to accelerometres, they sense how much you toss and turn, and based on that estimate the time you spend sleeping. They can also somewhat estimate the amount of deep sleep (restores body, dreamless) and REM sleep (restores mind, that’s when you dream).

In lab conditions, REM (stands for Rapid Eye Movement) and deep sleep amounts are measured by observing the activity of brainwaves. The numbers on your tracker, estimated from movement and, sometimes, resting heart rate are exactly what they are – estimations. But you can observe fluctuations and compare them to what you have done differently on a particular day. You may notice changes (or absence of thereof) based on:

  • Amount of stress during the day
  • Time when you go to sleep
  • Alcohol consumption (time of the day and amount)
  • Activity levels and types (time of the day and amount)
  • Caffeine-containing drinks consumption (time of the day and amount)
  • Exposure to sunlight and artificial light

All bodies are different. For some, three mugs of strong tea before bed won’t do a thing. For others, a few sips will spark off insomnia. Know thyself. The better you do, the better the decisions you will be making.

If a tracker can make you go to bed early and consistently wake up at the hour you want without feeling like you’ve been run over by a tractor, it’s doing its job.

I need to estimate my recovery

Recovery has always been a tricky thing to estimate. There are many factors to recovery, with sleep being a ginormous one, but trackers are learning to implement other factors.

Fluctuations in resting heart rate have been used to evaluate training capacity for generations. The old-school way to estimate recovery included a combination of the athlete’s sleep log, resting heart rate log, self-reported wake-up energy levels, as well close observations of how the body behaved during warm-up and cool-down.

Most trackers provide automated sleep logs. Some also provide the daily resting heart rate. However, technological advances give us another metric that was not available in old-school tracking: the heart rate variability (HRV).

The heart rate variability, in essence, is almost imperceptible time variance between your heart beats, a metric that indicates how resilient your nervous system is and how well is it capable of adaptation. The higher it is, the more strain (from exercise and daily challenges) it can take. Low HRV is often present in individuals with chronic conditions, overtrained athletes and beyond stressed hard workers. As with the previous metrics, we are looking for trends: if HRV is getting higher, notice what you are doing differently and do more of it. If it is going down, you may notice a correlation with some decisions that don’t serve recovery – late time to bed, new exercise regime or poor food choices (perhaps, that three-days outdated yoghurt wasn’t such a great idea after all).

Trackers measure HRV by means of either a chest strap or an optical sensor. The accuracy variables based on hardware, software and position apply here. HRV is a little tricky for optical sensors, but the recent generation seems to do the job.

One such tracker on the market that goes by the name WHOOP is designed for recovery purposes only. It calculates daily strain, daily recovery and sleep needs based on 24/7 recording of what you do and how much you sleep. The recovery scores are based on a combination of quality and amount of sleep, resting heart rate and HRV. It also makes you manually report how well you feel after sleep and whether you smoked, consumed alcohol, drank caffeine-containing beverages before sleep or shared your bed. A time-tested combination. Strain scores seem to be based on daily average heart rate and, perhaps, some other metrics. To improve the accuracy of intra-workout heart rate readings and strain score calculations, the device was designed with an option to be worn on the forearm or upper arm. In a way, it does the heavy lifting for you, so you don’t need to crunch the numbers.

My discontinued Polar A360 (current A370 works in the same way) is measuring recovery in a different manner. It requires you to lie still for 5 minutes with the chest strap on, while it measures your resting heart rate and HRV for the duration of five minutes. After that, it will tell you your level of cardiovascular “fitness”. This can be done on a weekly or bi-weekly basis to see if your training schedule is serving you or breaking you. Fairly user-friendly feedback, and, again, no need to crunch the numbers.

Just like with sleep, if the tracker can gather recovery data that breeds insights, it is half job done. The real outcome lies in what actions you take based on that data. If you’ve improved most rituals that influence your performance and are enjoying your training sessions more than ever, who cares if numbers are inaccurate?

Practical advice on selecting a tracker

By now you may have asked yourself the necessary questions and know exact answers as to what outcomes you are looking for. Maybe, you even googled a good bunch of trackers and wonder which one is right for you, as all of them tend to do different things.

Keep your eggs in one basket

It is always better to select a single device that will cover all your bases. You may be tempted to buy a few and switch between them, but this way you will likely end up wearing none at all after a few weeks. Consistency is critical in getting to where you want to be, and it equally applies to tracking methods. Consistent use creates a habit while monitoring on the same device means you will get better consistency in your data readings.

If you want to use your tracker for all the reasons mentioned in this article, you will need to ensure it can get all the jobs done. It must be lightweight and comfortable enough for you to wear it to sleep, what will likely not happen if your tracker is a heavy-duty multi-sport GPS wristwatch capable of sleep tracking. If you plan to track your heart rate during exercise sessions and log them in, it needs to be able to pair with a chest strap, a bicep strap or be able to migrate itself upwards. If you want to track recovery, it needs to have an option for that too. Perhaps, you may want to set up buzz notifications – as reminders if you know you don’t drink enough or if your goal is to wake up at 5 AM and you don’t want to wake up your significant other.

Battery life

It is the most important feature to consider. The less your tracker leaves your wrist, the more consistent data you will have, the fewer hours you will be losing to an unexpectedly dead battery and charging times, and the less you will forget to put it back on.

Consistent optical heart rate tracking eats a lot of battery, and you may need to charge daily. In most cases, this feature serves no purpose for your outcomes. You don’t need it to do what you need to do. Consider trackers with at least a week of battery life or those that can be charged with portable charging packs with no need to be taken off the wrist.


While you probably will not be diving to 50m depths, there will be times when you will forget to take your tracker off when you go shower or jump into the pool. It is better to have at least some waterproofing. Most trackers already have that. There is no particular need to go for the largest available waterproofing score even if you plan to take your tracker to the pool and record your swim sessions. However, if you do that, make sure your tracker can be paired with a chest strap, as optical sensors don’t tend to work that well under water. Also, make sure that the transmitter on your chest strap can record data as Bluetooth connection between the tracker and the transmitter can be inconsistent underwater.

Considerations for sports and lifestyle

While we covered most things relevant to the choice of your trusted digital ally, small details do matter.

Do you have relatively easy access to the service centre? Even the best quality trackers need a battery replacement every few years. You don’t necessarily need to buy a new one once something breaks.

Can you buy extra bracelets? Those things get dirty, and you may want a spare for when you wash the other one. They can also rip and rub off at the edges. Consider silicone or military-grade nylon bracelets – they are less likely to give you a rash.

Do you need to track recovery and one of your sports is martial arts? Then, you can’t have anything on your wrist for safety reasons and may need to hide a heart rate transmitter under a sufficiently padded sports bra or have a contact sport-friendly padded upper arm sleeve compatible with your tracker or the optical heart rate sensor. Your tracker needs to be capable of collecting data under these adjustments.

There are many clever trackers available. The only thing they will never be able to do for you no matter how far the technology advances is to take action in your stead. Choose wisely.

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