The truth about fitness trackers: are you running an extra eight miles?

If you’re a long-distance runner, you may find yourself relying on fitness trackers to track your progress. However, you could be seriously underestimating the distance you have run – by up to 32%! A recent Which? study earlier this year, ahead of the London Marathon, revealed that some of the most trusted brands may not be recording your distance as accurately as you think…

Why is it important that a fitness tracker is accurate?

Well, if you’re training for a marathon (26.2 miles) 32% of the distance is 8 miles. Imagine you ended up training to run more miles than you actually needed to. Or likewise, were led to believe that you were running the correct distance only to find out on the day you weren’t training to run far enough. The time and energy put into this, all for nothing. The assumption that some of the biggest names in the fitness tracker industry will be reliable may be wrong and price doesn’t always mean accuracy.

Fitness trackers either use motion tracking or GPS to track your distance.

Those that rely on GPS will either be GPS-enabled or use the GPS on the phone it’s been paired with. In the Which? study it was found that trackers that used GPS were the most accurate. It seems logical that GPS will track distance more accurately, after all it can track your exact location.

If your tracker isn’t GPS enabled or doesn’t use the GPS on your phone, then it will track your steps using motion sensors. The number of steps you take will then be multiplied by an estimated stride length, calculating your distance. The massive problem with this is that we all have different stride lengths. Someone who stands at 5’4” will travel a much shorter distance per stride than someone who is 6’2”.

Which fitness trackers are the most accurate?

The Which? study found that the most accurate tracker was the Apple Watch Series 1 with only a 1% inaccuracy. Another reliable choice is the Huawei Watch 2 Sport with, again, only a 1% inaccuracy. For both of these trackers, at the 26.2-mile mark it would show you had run 26.5 miles. The Garmin Vivoactive HR comes in third, underestimating your distance by -2%. The tracker would read 25.7 miles when in reality you had actually run 26.2 miles.

The worst performing fitness trackers include the Misfit Ray and the Garmin Forerunner 35. Both have a -32% inaccuracy between the distance run and the distance displayed on the tracker. When wearing these trackers, if you had run 26.2 miles the tracker would only read 17.8 miles. This is a massive inaccuracy and would definitely affect your training. You’d be disheartened to read that it was taking you far longer than expected to run the marathon distance and you’d be pushing your body harder and further than it realistically needed to go. All for the sake of your watch reaching 26.2 miles, even though you smashed that a long time ago.

Which fitness tracker brands are the most accurate?

Looking at a number of fitness trackers per brand, Which? were able to create the following table highlighting overall brand averages and inaccuracies (based on the average for models tested by the following brands):

Interestingly, Garmin has appeared in both the most and least accurate trackers. Garmin is a well-known,  trusted brand but it is interesting that there is such a difference in two of their fitness trackers. If you are in the market for a new tracker you should not only compare different brands but also trackers within the same brand.

There’s a fantastic infographic provided by Which? at the bottom of this post, highlighting how various fitness trackers would read if you were to run a marathon.

So, should we just stop using fitness trackers?

In short: no.

There are many advantages to using a fitness tracker, assuming you do you research before purchasing. As mentioned before, GPS fitness trackers work much better than those that rely on motion sensors.

If you do purchase one that relies on motion sensors, there are still many advantages but it’s worth using them as a guide alongside other methods, increasing your accuracy and ensuring you’re meeting your targets.

What we’ve seen with some is that it encourages them to be more fit and healthy than they’d normally be. Many fitness trackers give the user daily goals and they make it their mission to complete them. This might be getting up and moving about more often than they normally would, walking somewhere instead of driving, or even making a point of working out when they may not normally.

Companies such as Vitality have offers in place that allow you to track your steps and fitness with your fitness tracker in order to earn points each week that translate to free cinema tickets & coffee, as well as towards discounts and even cashback at the end of the year. If that encourages someone to be more fit than they normally would, it can’t be all bad!

If you’re interested in an honest review of the Apple iWatch Series 3, Shannon wrote one for Jogger earlier in the year.