By the very nature of the game of Tennis, most of the top players are athletic and have to be in this day and age.
Some of you are correct in mentioning the women. Mauresmo, Henin Hardenne, Venus, Serena, Clijsters are among some of the finest athletes in the history of women's sport.
In the past, Graf and Navratilova are easily up there with the finest ever women athletes like Jackie Joyner Kersee and Heike Drexler.
Sharapova and Petrova have been working hard to improve their movement. Great past players like Sabatini and Novtona were fine athletes. Elena Dementieva and Myskina are great athletes. I feel Kuznetsova could be too but just needs to be a bit more lean to move quicker around the court. She has the power.
Mary Pierce, Lindsay Davenport, Monica Seles covered for their lack of athletic ability with great shotmaking, therefore trying to put their opponents on the backfoot before their opponents put them on the backfoot. Davenport always got frustrated if she couldn't put an athletic player away quickly, and would start making errors as a result.
For the men, again, most of those guys are athletic except Ljubicic. Saampras and Becker and Edberg were the most athletic players of the mid 1980s to mid 1990s. Rafter was also very athletic. Krajicek was a great mover for a guy who was 6 foot 5 inches. Michael Chang of course. Henman is actually very athletic and moves smoothly around the court. Cedric Pioline was also athletic and loved jump smashes. His father played volley ball and his mother was a gymnast. Thomas Muster would run all day if he had to. Pat Cash and Yannick Noah in the 1980s were very athletic. John McEnoroe said in his book that his movement was underated. Lendl was athletic but not explosive, therefore he was always vulnerable to players who have a big game.
Another person I question is Roddick. I've questioned how athletic he really is more than once His movement can be a lot better. He didn't grow up on clay courts but has played well behind the baseline so I question that. Roddick also doesn't employ the classic play for players with great forehands. When Sampras was young, he would love to hit the kick serve to the backhand on the advantage court, get the return and then smack the forehand down the line for a winner. Sampras brought that tactic back into his game in the 02 US Open against Haas and Roddick, it was a good change up to serving and volleying. Federer does it too. To do that you must have excellent footwork to make room on the backhand side to hit the forehand down the line, you have to make quick little skips. Roddick tends to hit the inside out forehand instead, many times straight back to his opponent which means he's vulnerable to the backhand down the line. I've seen it happen to him so many times. So, I'm not sure his movement is top quality consistently.