He plays a lot of tennis, but for the rest he says himself he's a bit of a lazybone. I know Marisa said last time the Chinese media were reporting he was spending much more time in the gym than the other players, but I was surprised because he and his physical trainer Paul Quétin both say in interviews he doesn't want to work on his condition during the tournaments. Gilles also meant in the video interview after Bercy he just goes jogging a couple of times a year during the off season.
But his former coach Potier probably used to stress that too much in the past, he was really poking fun at him, he had also hung a poster at the entrance of Roland-Garros saying "Gilles, the gym is that way ->", etc. So Gilles had a terrible reputation in that regard, that's why he often stresses now he does train hard! And I don't doubt he does to have the results he has, but I don't think he is a hardworker à la Robredo & Co.
A guy after my own heart, I knew there was a reason why I liked him