Talking of facts, or lack of...
This might be a made up statistic but I'm sure it was said David Beckham would run up to 15km in a match and presumably more in training. Nearly a half marathon every week could be considered as running quite hard.
I wonder if it is more to do with the amount of sports science and personal doctors applied to sports such as cycling, swimming or long distance running that more athletes are picked up with having this whereas footballers, tennis players et al just get on with it?