With all the leaked photos going on with the iCloud (no, this is not a post announcing my affiliation with a leaked celebrity nudes website), I saw a post that piqued my interest: “Fitbit Charge Fitness Tracker Revealed in Leaked Images.” The post was from “Mashable,” but I think the other place that posted it was from “You Have to be Seriously Bored With Your Life To Read Our Articles dot com.”
The battle between Fitbit, Apple, and Google for fitness tracking devices shows the demand for these fitness trackers among the public, and makes me raise an eyebrow for it’s demand. I’ve always wondered how accurate these trackers are, and in this week’s blog I’m going to dive in deeper and find just that.
Because these fitness trackers are multifunctional (tracking statistics like sleep duration, sleep quality, calories burned, steps taken, and activity time) I am going to break this down category by category for easy digestion. I will ,however, only break down what I believe are the two most important and popular trackers: sleep and calorie burn.
Please note that I DO NOT, nor have I ever, owned a fitness tracker, and am purely writing this from a research based stance from what’s available in the literature.
Sleep (Duration and Quality)
What the fitness trackers say: Measure how long and how well you sleep.
How does this work? Using a built in accelerometer, the fitness tracker senses any movement that takes place during the night, and notes that any movement taking place puts you closer into the “poor sleep” category.
What the research on sleep duration says: The gold standard for sleep duration and quality is a lab test called polysomnography. Compared to this test, the accelerometer is EXTREMELY juvenile. The accelerometer is very easy to trick. In a 2011 study, the authors found that the Fitbit overestimated sleep duration by an average of 67 minutes. In another study on children done in 2013, the tracker had the opposite effect, underestimating sleep duration by an average of 109 minutes.
What the research on sleep quality says: The fitness trackers rely on movement to translate into sleep stages. However, sleep stages are influenced solely on brain activity. Common measure of brain activity is the EEG, which measures your brain waves. Also, muscle tone and eye movements also measure REM sleep. The fitness trackers also state they can measure levels of REM sleep using the heart rate monitor, when in fact heart rate is not the same as brain waves. Sure they can influence eachother, but to use solely this measure is misleading.
Calories Burned (Caloric Expenditure)
What the fitness trackers say: Measure how many calories you’ve burned.
How does this technology work? Using an estimated basal metabolic rate (calories burned without activity) that is taken from height, age, weight, and gender, combined with estimated calories burned during physical activity, the fitness trackers are able to find calories burned during the day.
Just how accurate are these estimations? While height, age, weight, and gender do have effects on caloric expenditure, the acceptable resting variance among practioners is + or – 10%. This could be the difference of 100-400 calories, which is quite a bit. There is also strong evidence suggesting body composition is a much better determiner of resting metabolic rate (or calories burned without activity) you can read in the literature HERE (), HERE (), and HERE (). Other determinants of your resting metabolic rate include genetics (research HERE), amount of muscle mass (research HERE), thermic effect of feeding (calories burned through your food choices) (research HERE), hunger, meal size, and daily caloric intake (research HERE).
Calories Burned During Physical Activity: There wasn’t a whole lot of research on the subject, most likely because it was too tough to hook someone up to a metabolic rate measuring machine such as “The MedGem” to measure your metabolic rate during physical activity. However, intensity directly influences calories burned during activity suggested in this article HERE (https://sites.google.com/site/compendiumofphysicalactivities/corrected-mets), and intensity is a very subjective experience. This will cause a large amount of variation because what is “hard” for you may be considered “moderate” for someone else. Further, in fitness tracking software such as My Fitness Pal, the option of selecting intensity isn’t even available.
So Are Fitness Trackers Worth It?
For sleep quality and duration, I would say no. For calories burned, it depends. If you are trying to just be more active because you are extremely sedentary then yes, using ballpark markers to track your levels would be great. If you are serious about your goals, a high level athlete, or very type A, I would say don’t waste your time. The variation is just not worth the headache. I would, instead, use your body as an experiment and try out different caloric intakes with different volumes of physical activity. Based on whether you gain body fat or lose body fat, you can adjust accordingly.