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Is Your Fitness Tracker Lying to You?

Have you ever felt frustrated at the end of a workout because you forgot to set your fitness tracker going? That feeling that exercise only ‘counts’ if your wearable has recognised it, is all too familiar to many of us! How about looking at your smartwatch at the end of the day to see you’ve fallen short of your step target, only to walk up and down the street a few more times to nudge it over the edge? I’ve seen people literally get up from the dinner table at social occasions to shamble about, because their watch it telling them they’ve been sedentary for too long! This prod of motivation to get a little more movement into our day can be hugely beneficial to some, helping them achieve the minimum (albeit arbitrary) recommended 10,000 daily steps. But are we relying too heavily on these pieces of kit that are inherently pretty inaccurate?

Independent research into wearable fitness trackers shows them to vary in their accuracy calculating data, but also consistency. Some aspects of tracking appear to be more accurate overall than others, and the type of technology the device contains will make a big difference...

Let’s Start With Step Counts

In order to estimate steps, devices use accelerometers, gyroscopes and altimeters to collect data, and combine them with algorithms to formulate a step count. Of course, we move in all kinds of ways during our day and some devices are better at differentiating between incidental movements and actual steps. Manufacturers also use different sample data and algorithms, so two wearables would report different step counts, even if worn together. Anecdotally, in my experience moving from a Fitbit to a Huawei device, I saw a drop in step count with the latter. I have also read that devices generally are less accurate at recording steps when you’re moving slowly, or if you have an unusual gait… not particularly inclusive.

If you use your tracker for runs or walks and want more accurate splits, my advice is to get a tracker with GPS either built in, or at least with connectivity to your phone (and don’t forget to take your phone with you!). This is shown to at least increase the accuracy of distance travelled, so you can compare your pace. Devices without GPS are just estimating distance, so really aren’t a good choice for you.

Calories (Burn, Baby Burn!)

When we look at calories burnt through exercise, unfortunately the overall accuracy further decreases. When you first set up a device it asks for vital stats such as height, weight and age. It’s important to input your personal data honestly in order to give the device a fighting chance. It then uses these details, along with research data and the measurements it’s collecting from you such as heart rate and distance travelled, to formulate the number of calories burnt.

As we all know, the human body is a complex and highly individualised thing. Some people are highly efficient metabolic machines, conditioned to an exercise and therefore use less energy in completing it. Others are not. Energy expenditure is so nuanced, it’s not surprising to hear that fitness trackers are anywhere between 9.3% - 23.5% inaccurate in this area. Realistically that means that if your device says you’ve burnt 300 calories, this could actually be 230 calories, 371 calories or anywhere in between. This becomes a problem if you’re then using this data to dictate how many croissants you’ve ‘earned’ as a result of your workout, potentially leaving you in a calorie surplus despite your best efforts.

I’ve understand that trackers find calculating calorie burn for slower exercises particularly difficult, so there’s probably no point in even reading the data for weight training sessions, or the majority of exercise classes. Remember, your device is probably not consistent in its inaccuracy, so you shouldn’t even use the calorie burn data to compare one session to another. My best advice is to set the screen so it doesn’t display calorie burn. Instead, monitor more accurate data such as heart rate, and what your rate of perceived exertion is (how hard you feel you’re working, using a scale of 1 to 10 perhaps).

Be Picky for Better Results

Great advice is to buy the product best suited for the task you want it to track. For example, some of the most accurate devices for step counting are clip-on pedometers worn at the hip (including your smartphone when worn in a hip pocket). The location of the device negates the issue of incidental arm movements muddying the step count. Or, if you’re specifically looking to measure running splits, devices which focus on accurate distance measurements (such as those by Garmin) are a good idea to seek out. Maybe sleep patterning is your interest. In that case, perhaps a monitor that straps to the chest is really what you should consider.

Take the Long-View

It’s not all doom and gloom for that fitness tracker you chose because of it’s jazzy strap! So long as you’re not wedded to the data it churns out, using your device to highlight trends can be super-handy. I have a number of clients that keep an eye on their resting heart rate week to week, and notice it trending down as a result of their exercise programme. This is a fantastic indication that their general health is improving, and serves as welcome positive feedback. Problems arise when we use the data as gospel, become fixated on the numbers and obsessive about improving them, or disheartened by our device to the point it affects our mental health. Use the calorie counter as a fun estimate of how much energy you might have used, keeping in mind that the numbers could be 23% higher or lower than given. And if you’re a numbers orientated person, grab the best device you can find for the job, and use the data to identify trends over time.

Tips For Success!

Apart from buying the wearable best designed for your focus, there are a few key points you can apply to any device:

- Wear tightly for most accurate heart rate measurements. The device should feel snug, but not uncomfortably tight.

- Wear watches on your non-dominant wrist to avoid arm movements muddying the data.

- Input as much additional personal information as you can, accurately (weigh yourself and adjust on your app if you change weight for example). Some platforms also allow you to input individual specifics such as stride length, vastly improving the accuracy of data. So it’s worth checking out exactly how customisable your system is.

In short, your fitness tracker is not so much lying to you as being creative with the truth!


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