That depends on what you rate as a physically fit person; is it some one who can swim 50 laps of a 50 meter swimming pool non-stop, or is it someone who can swim the 50 laps at the same pace as an Olympic swimmer? I (Michael Jenkins) would have a lot of trouble swimming 50 laps of an Olympic pool non-stop. Clocking my skating speed using my Garmin 405 GPS, in traffic, including stopping at intersections, I usually have a moving average of 15kph on Chariot Skates. Without traffic it is 20kph, but I have been at speeds of over 35kph with a strong tail wind. I usually overtake recreational cyclists. Over a 4 km course, my moving average on inline skates is around 15kph while on Chariot Skates it is around 20kph... and I know I’m not especially fit because there are younger, fitter skaters getting far better speeds on their inline skates.