[wasmitnetzen]

How can you know this "as a matter of fact"? Because your not-a-healthcare-device sportswatch tells you so?

[vbarrielle]

Not running, but in cycling we have power meters, and some workouts (eg 2 x 20' threshold) will definitely burn in the range of 800 calories in an hour. The energy measured by the power meter for this workout is 800 kJ for me (my threshold being around 260W). Now it turns out the conversion factor from kJ to calories is 1/4, but the body is only 25% efficient when producing calories for cycling, meaning one has to burn 4x the amount measured by the power meter. So that's 800 calories for this kind of workout, for me. I wouldn't be surprised if runners of similar fitness doing similar workouts had the same energy expenditure.

[wasmitnetzen]

I'm not arguing that your body burns that much energy, that follows from the first law of thermodynamics.

But whether that means that your body will have a calorie deficit of that same amount, that is much harder to prove.