Comment by lebuin

I think OP may be referring to the idea that the total number of calories burned in a day doesn't meaningfully change under a workout regime. Working out does burn calories, but after a few session your body starts to compensate by burning less calories in other areas (e.g. immune and reproductive system). The net result is close to zero, except in very demanding workout regimes.

I don't have the background to fully evaluate how true that is. I read "Burn" by Herman Pontzer, which at least makes a very good case for it.