Well, I don't know, apparently married life also makes people fatter. So maybe it does have an impact.
Federer has been married for a while, though, I think? Did not seem to bother him before? Then it's true that Rafa, Andy and Nole are all unmarried.
Could it be that they decide to get married when they start caring a little less about tennis? That could explain it. But in truth I have no idea...
Ferru had better wait a little before he marries Marta, then
Though in his case being with the right person definitely helped a lot... While breaking up with the previous one had an immediate and devastating effect.