Calculation of Burned Calories

Calculating the burned calories during a workout is a common challenge for everybody who performs strength training. This is because there is no straightforward and reliable way to accurately calculate the burned calories in a strength training workout. The non-scientific, quick explanation here is that - during a strength training workout - you perform different exercises, in which you use several different muscles, which in turn have different effects on your energy consumption. Because of this, it is impossible to accurately determine the burned calories mainly on a factor such as your body weight or your heart rate.

In the industry, it is common to calculate the burned calories based on a formula and some key parameters of the workout. GymBook calculates the total calories burned in your strength training workout by using a gender specific formula provided by the Journal of Sports Sciences.


(Age x 0.2017 — Weight x 0.09036 + Heart Rate x 0.6309 — 55.0969) x Duration / 4.184


(Age x 0.074 — Weight x 0.05741 + Heart Rate x 0.4472 — 20.4022) x Duration / 4.184

When saving a workout to the Health app, GymBook uses the formula above to calculate the total burned calories and add them to your workout. The burned calories can only be calculated if all the needed parameters are available (see the table below). If any of the needed parameters is not available (for example, if you are working out without a heart rate sensor), the workout will be saved to the Health app without an indication of the burned calories.

AgeYour age at the time of the workout.Calculated based on the date of birth stored in the Health app.
Your weight at the time of the workout.Retrieved from the saved weights in GymBook. If there is no weight from the date of the workout, the most recent weight will be taken.
Heart Rate
(beats per minute)
Your average heart rate during the workout.Calculated based on all available heart rates inside the Health app during the workout period.
The duration of your workout.Estimated based on the duration of the first log and the time difference between the first and the last log.

Please keep in mind that the calculated value provided by GymBook is only an approximation to give you an idea of how many calories you might have burned, and is by no means intended to be used as an accurate indicator.