Think you burned 500 calories during spin class?
You may have to think again.
Research from Stanford University and the Swedish School of Sport and Health Sciences found that if you’re measuring calorie burn using a wearable heart rate monitor and fitness tracker — such as the Apple Watch or Fitbit, Garmin Watch— the calorie feedback is likely way off (1).
Though six of the seven devices tested produced accurate heart rate readings (within 5 percent), even the most accurate tracker was off by anywhere from 27 percent, the worst up to 93 percent when it comes to measuring energy expenditure!!! For activities like walking and sitting, the results are more accurate than for more intense pursuits, like spinning and running.
The point is, you’re not burning as much as you think you are.
This is backed up by a systematic review that looked at 158 publications and 9 different brands of wearables and concluded that "For energy expenditure, no brand was accurate" (2). They also stated that "Commercial wearable devices are accurate for measuring steps and heart rate, at the current stage of technology that is it."A further comparative study concludes "at present, mainstream devices are able to reasonably reliably measure heart rate, number of steps, distance, and sleep duration, which can be used as effective health evaluation indicators, but the measurement accuracy of energy consumption is still very inadequate. (3).
Why do we want to stress this so much?
Because we would hate to see your weight loss efforts to go to weights by you "eating your calories back" (the calories that you didn't actually burn).
Or you feeling like you need to 'work off' any food that you ate, feeling guilty and gross about yourself.
Why are these devices so off?
Well mostly, because every body and everybody's body is so different.
Plus, these devices don't know if this is your very first time running those 5 miles or if you do that every day (adaptation), they don't know your dieting history (are you a yoyo dieter or not), your body fat percentage (at least most of them don't) and so on...
and all these things do play a big role when it comes to the energy that you are expanding for physical activity.
Does that mean you should not pay attention to calories at all?
We still very much believe in the value of calorie awareness - mostly when it comes to food intake (since it is so much easier done to overeat 300 calories than it is to burn 300 calories) - but we are also aware that it is indeed very important to take your overall activity level into consideration when it comes to assessing your maintenance calories/ calorie deficit or surplus.
However, we prefer to give you
equal calories regardless of where you exercised that day or not (you may have refeed days from time to time which has nothing to do with 'calories burned during exercise')
simply taking your overall activity level into consideration (frequency, duration, intensity, history...).
Should I not bother with an activity tracker then?
We still believe activity trackers have value for the exact points mentioned above: tracking steps, heart rate (on occasion) and sleep (if your tracker can do that).
Steps not for the 'energy burn sake", but for the sake of staying somewhat active even with a sedentary job and for keeping daily activity more or less the same from day to day, especially in a weight loss phase when unscheduled exercise tends to naturally want to decrease.
Hopefully this encouraged you to be less detached from you fitness tracker, trusting that consistency with training and your nutrition protocol will take care of your goal rather than feeling like you need to adjust things every day or 'out exercise' your nutrition.