22 million. That's how many fitness trackers were sold last year. You might even own one of them. Think that's a staggering number? Try this one - it is estimated that 130 million more will ship out by 2018. Sales of wearable devices are expected to top $50 billion PER YEAR by then.

With numbers that like that on the table, wearable fitness accessories are clearly becoming a huge business. Interested parties are currently looking for ways to incorporate them into the healthcare industry. And we featured them in a recent article here on the CFS blog. That's how you KNOW you're going places! ...Right?

The Ki Fit MonitorOn the surface, all of this fitness wearable love sounds like a really great thing. Wouldn't the world just be a better place if everyone kept track of their exercise (or lack thereof)? It used to be that to track your workouts, you had to write down notes, check mapquest for distances, and math out the results to see just exactly how many twinkies you'd burned off. Now your fitness wearable handles it all with GPS and motion detection. If you wanted advice on how to go about your routine, that used to require talking to a personal trainer - or at least doing a google search. Now pre-programmed routines are syncronized into your tracker and smartphone.

A couple of questions arise, however. First, are these devices really accurate? Who is testing these things? And secondly, how effective are fitness wearables in helping their owners lose weight and get in shape?

Fitness Wearable Accuracy: Rough

Anna Magee, editor of women's health magazine Healthista, decided to put several fitness wearables to the test.

It started off innocently enough - Anna typically wears a Nike Fuelband during her workouts, but she had recently gotten a Misfit Shine to review. One day without giving it much thought, she took off on her 30-minute circuit workout wearing both of them at once. The results were slightly alarming, and sent her off on a multiple-device testing spree.

"After doing these activities, I noticed some 250 calories’ difference in the number the Nike FuelBand said I burned and that recorded on the Misfit Shine," says Anna, "While the Nike Fuelband claims to only measure ‘active burn’ that done while being active and the Misfit Shine measures all calories burned, I still had no idea which one to believe."

"People buy these activity monitors assuming they work.."

Gregory Welk, a professor of kinesiology at Iowa State University, also launched a barrage of fitness tracker tests as a research project in June of 2014, citing a lack of published data regarding their accuracy.

"People buy these activity monitors assuming they work, but some of them are not that accurate or have never been tested before. These companies just produce a nice-looking device with a fancy display and people buy it," says Welk.

His results showed that some trackers calculated calorie burn up with up to a 23% margin of error. To put that another way - if your daily calorie expenditure is 2000 calories, 23% is over 400 calories of potential error.

Anna contacted both of the companies that created her trackers - Nike and Misfit Shine - requesting copies of their studies and research proving that the trackers are accurate. Neither company provided any documentation. So naturally the next step was to collect as many different trackers as she could get her hands on and test them all!

Her selection included a number of big names: Jawbone UP, Fitbit Flex, Ki Fit Monitor and Garmin Vivofit to name a few.

"I’d wear them all at once for a few days to see how big a difference – or not – they would show in calories burned, the main thing most of us are worried about when it comes to tracking activity," says Anna, "There was a 2-500 calorie range between them with the Misfit Shine saying I had burned 1841 calories and the Garmin VivoFit stating I’d burned 1393 calories."

500 calories' difference is quite a large gap. Too large to simply shrug off. Unwilling to stop there, Anna proceeded to open a can of science on her pesky trackers.

The Indirect Calorimetry (IC) Machine

Anna hooked up to IC in the lab at University of Bath - with all her trackers along for the ride.In the science of movement field, the gold standard for measuring calorie burn is a machine called Indirect Calorimetry. It's not as sexy as Anna's collection of fitness trackers - the jogging-while-wearing-a-snorkel look went out in the 80's (and that's saying something) - but the IC machine has been used as the end-all be-all of caloric measurements for over 100 years.

"My experiment involved doing four activities, walking on a treadmill, cycling on a stationary bike, typing and packing groceries and comparing the calories burned on the IC machine to the different devices I was wearing and seeing how they stacked up."

Her results were less than stellar. For one thing, exercises like typing registered higher than reality because the trackers on her arms picked up a lot more wrist motion. Meanwhile the trackers had little at all to say about the cycling, as this involved a lot of lower body motion while the arms and wrists stayed relatively stationary.

Another issue of course, is the fact that our bodies burn calories differently depending upon gender, body type, and a host of other variables that extend beyond the simple "height and weight" calculations most trackers run on.

When it comes down to it, any fitness wearable that can stay within a 10-20% margin of error is doing well.

Anna's final results for some of the trackers came in significantly worse than that. She has posted details in her write-up on the experience, as well as some recommendations. It's a good read, and will give you a lot more insight into how these gadgets actually work.

What About Willpower Improvement?

Wearing a fitness tracker does more than just keep tabs on your "approximate" calorie burn. It also serves as a reminder that you are, in fact, burning calories. One of the big selling points for fitness wearables is that they provide you with an instant-gratification sort of reward for your healthy activities. But now that there are a host of them on the market, have their wearers shown any appreciable average health benefits?

Well, "wearers" may be a trick question. Studies have shown that more than half of buyers stop using it - a full third of those within the first 6 months.

A study published earlier this month by Dr. Mitesh Patel with the University of Pennsylvania targeted this very line of questioning, and picked up on a number of things to seriously consider if you're in the market for a fitness gadget.

The first - and perhaps most obvious - point is that to use a fitness wearable device, you must actually WEAR the device. Before you scoff, think it over - every extra step you must take each morning as you start your day is another potential source of failure. While it may be second-nature to carry your smartphone, snapping on a fitness tracking bracelet isn't on the same level of priority. And it's also liable to end up in the back of your glove compartment, beneath the cushions of your couch, or on the floor of the locker room at the gym - to name just a few likely places.

Second, and on the same topic – simply making sure you wear your snazzy new device is the easy part. Next, you’ll need actually GO to the gym – or at the very least, increase your daily activity levels – if you want to see any real health improvements. That makes two new daily requirements to see any benefit from the fitness wearable. Most people who buy one – honestly – aren’t going to hold up their end of that deal.

What Have We Learned?

What it all really boils down to is exactly the point we made when we covered a variety of fitness trackers last time – having the data at your fingertips can help you stay motivated, even if that data isn’t always spot-on accurate; but ultimately the success or failure of your fitness plan relies on your decisions and your commitment to it – not the particular brand of tech you use to track your progress.