Double the calories?

Question regarding calories burnt report.
I have a Suunto Sport Spartan. After each workout, the calories burnt form the Suunto are always (about) double than those reported by TR.
Example: I did Garfield - TR reports: 599 KJ, Suunto: 1213

It’s consistent across all my workouts. I know my setup (weight/height) is correct on both.


BTW, I do think that the TR numbers are more accurate, but how do I really know that?

If you are using a true power device then the TR number is more technically correct.

Heart rate based measures can be off by a very long way. I’ve always found the firstbeat system used by Garmin devices is close enough… Or at least closer than any other guess.

Note that an accurate HR calorie estimate is dependent on having a good idea of your true HRMax (the default 220 minus age formula is the average for the population as a whole, but is #$%^ at predicting the maximum for any one individual).

My understanding is that HR-based caloric expenditure is not really all that useful, as caloric expenditure is more a function of work done than how hard it was for you to do that work. That is, to put out 300 watts (or to squat X pounds, or any other fixed unit of work) will require basically the same caloric effort for all people, regardless of how hard it happens to be for them. This ignores the concept of “efficiency”, but my reading of the research shows that the efficiency factor is pretty small overall.

As power = work done / time, when you are training with a power meter you get a pretty accurate calculation of the energy expended in a workout. Although there is still some variability in efficiency between people, generally you power related calorie count will be a lot more accurate than other estimated calculations.

Rule of thumb:

Calories = average power/hr * 3.6.

i.e. 222w avg (1hr) * 3.6 = 800 calories.

Take your average power with a pinch of salt if it’s VP or the credibility is questionable/not true power.