• Ana Bailoni

Can you trust your FitBit?

A member of the our gym, Karen, arrived for her class last week after being absent for several days. Like every good coach, I expressed how much we missed her, to which she quickly replied: "don't worry! My FitBit told me I was the most active last week when I didn't even come to the gym!" It was her birthday the week before and she had all kinds of celebrations, including a night full of libations and tearing it up on the dance floor.

Karen was joking, but she really did want to know: "was I really being healthy if I was drinking and eating like never before, but my activity tracker told me I also burned calories like never before and I got triple the steps from my normal days? I certainly didn't feel healthy, but I was getting non-stop CONGRATULATIONS ON YOUR FITNESS! messages from my wrist watch. Ana, do those numbers really count?"

Do the numbers my FitBit track really matter?

Sounds like a job for... #RioInvestigates!

Are wearable activity trackers accurate?

Activity trackers are gaining more and more popularity, and they're really fun to use, but he truth is there is very little published research demonstrating the validity of these devices, so it's hard to say definitively whether or not they're giving you correct measures.

Here's what we do know.

Steps - pretty accurate: most high quality devices count your steps pretty accurately, up to about a 10% error rate. Arm movements and variation in strides and speed may change these counts, but generally they're accurate enough.

Daily calorie burn - nope, don't trust it: this is where we run into trouble. In the studies done, the error rate for daily energy expenditure was from 27% to 93%! That's quite a large margin for you to deposit your calorie intake on. The reason for this is the nature of the variable being measured: daily energy expenditure (calories burned) is a very complex phenomenon that depends on hundreds of factors, including age, sex, height, weight, muscle mass, body fat percentage, hormone cycles, nutritional state, activity level, aerobic conditioning, and many many others. It's not a straightforward variable that can be easily calculated by an algorithm.

Heart rate - really accurate: this one has an error margin of only 5%! In other words, it's accurate 95% of the times when compared to findings from an electrocardiogram. That's pretty trustworthy! It kept that margin for heart rate at rest and at steady state activities like walking or running. It starts getting complicated, however, if you're trying to track high intensity acitivities or athletic type training, mainly because of the position of the tracker on the writs. For those types of activities, you're better off wearing a chest strap heart rate monitor.

You can read more about these studies here, here, and here.

What do you mean by "fit" and "healthy"?

Now that we've established that we need to take those numbers with a grain of salt, let's answer Karen's question: do those numbers really matter?

Steps: there seems to be a lot of misconception around the idea of "getting in my steps." I saw a video on Facebook of this woman going on a rant in her car because she forgot her FitBit at home and she refused to go into Target without it. She was in her car, in the parking lot, waiting for her husband to bring her her FitBit. That's a patient man right there. Ok, this is an extreme example, but don't you kind of identify with that woman?? There's a game-like compulsion with hitting those goal numbers, ins't there? But is there any real fitness and health value to "getting in those steps"?

Is there a fitness threshold that you reach when you hit 10,000 steps a day? Not at all. That number is quite arbitrary, actually. It's become the convention because when step counters were first being sold in Japan back in the 1960s, they were marketed with the name "mango-kei," which literally means 10,000 steps. For some reason, that number stuck, and almost 60 years later we're still doing laps around the house to hit the 10,000 milestone.

Honestly, it's inconclusive. There seems to be a general consensus that when it comes to steps, more is just more, not necessarily better. A person who consistently walks 15,000 steps a day is not necessarily healthier than one who only walks 8,000 steps. However, if you work a desk job and are lucky to get 4,000 steps in a day, increasing that to 6 or 7 thousand is a good thing mainly because you'll be sitting less and taking more breaks - which are generally good things mentally and physically.

Second, step count doesn't take intensity into account. Intensity is crucial for aerobic conditioning and other healthy adaptations of the body. Getting yourself out of that comfortable breathing pattern is necessary for physical fitness changes to occur. You can hit 16,000 steps a day and never once break a sweat - you'll be burning slightly more calories than you would in a 10,000 step day, but not enough to put a dent into your calorie deficit, and certainly not enough create the metabolic chaos necessary for body composition change.

Finally, steps don't taken into account other activities that don't involve taking steps, like swimming, biking, and strength training. I love this study by the Harvard School of Public Health on the health benefits of strength training as compared to cardiovascular training. In a sample population of 10,200 adults, the study showed that participants who did 20 minutes of strength training gained less visceral fat - a nasty, nasty kind of fat that's liked to heart disease and premature death - over 12 years than those who participated in the same amount of time of cardiovascular exercise alone.

So, do steps really matter? Not in the sense of having a specific number to hit. But if you increase your steps, no matter where you're starting, you are adding movement and blood flow to your day which can be generally beneficial. Will you torch tons more calories to get that lean, sculpted physique? Not at all. Go lift some heavy stuff and get yourself out of breath if that's what your'e after.

Heart Rate: Your resting heart rate is a great indicator of improvements in your physical conditioning. Generally, your resting heart rate should be about 55-70ish, the lower the better. When you're sedentary and become physically active, over time your resting heart rate will slow, indicating a better adapted heart.

Some people have naturally higher heart rates than other, and that's perfectly normal. Find your baseline, and look for improvements by checking to see if that number lowers over time.

Daily Calorie Burn (energy expenditure): this is the number to watch out for, and the one that will answer our friend Karen's question. You ever wonder why lean 22 year old guys who practice sports can eat whatever they want and still have a six pack? It's because their metabolism is crazy high and even though they're eating upwards of 4,000 calories, it's still not matching what they're body is burning just to exist. Go ahead and say it: jerks. (There are some other factors, like testosterone and growth hormone oozing out of their ears, but those just support lean muscle mass which leads to the fast metabolism. In the end, it's all metabolism.)

Anyways, Karen, probably didn't feel healthy because alcohol is a toxin and it generally makes you feel like garbage the next day, both physically and mentally. But she did burn a lot of calories by dancing and jumping around the dance floor with her friends. Was she in an energy balance? In other words, did she burn as many calories as she took in? Or did she burn more than what was in all the sugary drinks and late night pizza?

We'll never know. Unless she tracked every sip and bit in an app like My Fitness Pal, and we measured her metabolic rate with a very reliable lab-worthy metabolic analyzer, we'll never know if she danced enough to off set her calorie intake.

Overall, was she healthy and fit that night just because her device told her she was? I wouldn't say so. But will it kill her to have a one night extravaganza with her friends? Not at all, party on, Karen! But if she makes it a lifestyle, however, then the conversation changes.

Should I Stop Caring About The Numbers My Device is Tracking?

I wouldn't go so far as to say that. Binary thinking is the enemy of long-term health and fitness.

Binary thinking is the number one enemy of long-term health and nutrition.

When it comes to the diversity of human biology, behavior, and culture, there is rarely an absolute right and an absolute wrong. There are usually multiple factors that make sense only within a context.

Activity trackers are one of them - they need to be evaluated within a context. I believe these devices are a great acquisition! It creates awareness where there was none, and where there is awareness there is space for choice.

If you move a little more than you did before because your FitBit made you feel bad about sitting so much, you're winning, even if you're not beating your friend's 17,894 steps.

If you move a little more than you did before because your FitBit made you feel bad about sitting so much, you're winning, even if you're not beating your friend's 17,894 steps.


  1. The numbers surrounding our health and fitness don't define our health and fitness. They're just tools for creating awareness and empowering change.

  2. Technology is limited. Take the information with a grain of salt, and always within a context.

  3. There is no ONE thing (not a food, not a magical number of steps) that will make us fit and healthy. Only the sum of habits will create our fittest, healthiest selves.


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