Are fitness trackers accurate?

Should I include them in my calories burned and account for them in my food intake?

First of all, your metabolism is way too complex to be captured by your fitness tracker. Secondly, the number of calories that you burn based on your fitness tracker is not likely the number of calories that you actually burned during your workout. There are TOO many variables involved and it is almost impossible to tell how much one actually burns during a workout (unless you are in a metabolic lab).

A study looking at the energy expenditure from fitness trackers across different activities found that the error rate was between 27.4% to 92.6%! That is a pretty huge range! Therefore, if you are eating back the number of calories burned, your progress will likely not go where you want it to. This is a mistake that many of my clients make.

However, your fitness tracker is NOT completely useless. It is still a useful tool. Since these numbers are likely to have the same error rate, you can compare them on a day to day basis. For example, if you burned 400 kcal on your workout today and the next day you burned 200 kcal, you can then assume that you worked out harder the day before. So, you are still using these numbers but not the EXACT number.

Accuracy of your fitness device also depends on the technology (heart rate, heat sensors, accelerometer etc) and the activity being carried out (steady state exercises are easier to capture compared to high intensity exercises).

To sum it up, fitness trackers are a good accountability tool and can help encourage healthy behaviours. But please do NOT factor them into your overall daily calorie intake.

I also don’t like to link exercise with the number of calories burned as exercise is MORE than just that. If you exercise just to burn off what you’ve eaten, you are undermining the importance of exercise and you will soon realise that over time, the math doesn’t add up.

Reference:

1. Shcherbina, A., Mattsson, C. M., Waggott, D., Salisbury, H., Christle, J. W., Hastie, T., … & Ashley, E. A. (2017). Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort. Journal of personalized medicine, 7(2), 3.