I have always been a sprinter, as I tend to work fast and tire early.
I can push myself to work longer but my normal working pace stays the same and, as a result, I can burn out and need a longer recuperation period.
My typical workday in the shop lasts about six hours now. There were much longer days in my younger days, but that was then.
I'm finding that I have to pace myself much more than I used to. More breaks, lower gears, actually stopping for lunch and sitting down to eat it. It can be distracting because if you are not having to concentrate on working sensibly", you can focus entirely on the job at hand.
But, as my wife points out, not crashing into the wall is part of the job at hand, like it or not.