There have been several people, men and women who run a marathon every day for months or even years on end. In that sense there is no upper limit, but those people almost certainly all have a genetic mutation which most people don’t that prevents lactic acid buildup.
“Fastest” does not mean the best endurance. You would be looking at the “longest”.
There have been several people, men and women who run a marathon every day for months or even years on end. In that sense there is no upper limit, but those people almost certainly all have a genetic mutation which most people don’t that prevents lactic acid buildup.