Do you understand that what you're describing is anomalous behaviour and ability. In Europe we have legislation to protect people against being forced to work for more than 12 hours at a time because this has been seen to be detrimental to health. I see no reason why your reported lack of external coercion makes it healthier.
With 3 hours of sport (what sport would that be?) you're describing a day of 17+ hours. 2 hours for meals seems pretty reasonable. Commuting, eg to the location where you do your sport would be extremely unlikely to be less than 30 mins. That leaves you < (!) 4½hrs for sleep, toilet, washing, keeping house, family/friends (except sport and eating with them), entertainment ... you don't tell us how many days a week but "keep that up indefinitely" sounds like you don't bother with weekends?
Another great example of how people don't realize how cognitively impaired they are is hypoxia, just look at how passionate the guy becomes trying to put square shapes in square holes, so passionate he believes he no longer needs an oxygen mask to survive. https://www.youtube.com/watch?v=ZpLi67NdD4w
How do you know this? Are you sure you aren't extrapolating your own energy levels and assuming everyone else feels as you do?
I know plenty of people with phenomenal drive, focus and energy who are extremely productive for much longer work days.
My own situation is a counterexample. I am at my desk at 6:30am most days, can easily work 14+ hour days virtually without a break, never sleep more than 5 hours a night, and can keep that up indefinitely. I also fit in 2-3 hours sport a day, which is also technically very demanding and needs full concentration. My body may get physically exhausted but somehow my brain just keeps going.
To be fair, the friends of mine who work such extreme hours are all passionate about their jobs, and are the ones in ultimate control of their working hours. They do it out of choice, not because their boss tells them to. If they didn't like their work, they'd find it hard to stay focused for 8 hours too.