How do professional tennis players stack up against the world's greatest athletes?

When sports fans get together over a couple of beers and talk about the world's greatest athletes, the conversation usually centres around the slam dunk, the 97-m.p.h. fastball, or, maybe in an Olympic year, the 100-metre dash. But rarely does the discussion involve the serve, the return, or the topspin forehand.

It should.

"Tennis is one of the most demanding sports," says fitness trainer David Donatucci, who has worked with players like Tommy Haas and Jelena Dokic as well as athletes in many other pro sports. "There are incredible challenges placed on the body, and there's a huge mental aspect, too."

In other words, tennis is no sissy game. But will barflies ever get it? Will they raise a pint in honour of Agassi's return or Serena's speed?

Maybe this will change their minds: We took a few of the common denominators in various sports and compared top tennis players to some of the world's best athletes.

Power: Pete Sampras vs Randy Johnson: Both of these players can bring it — a 100-m.p.h. fastball and a 130-m.p.h. serve are equally scary. Well, it's Johnson who's really scary. The guy's not afraid to throw some chin music or even plunk a batter. But while we wouldn't say it to his face, we will say it behind his back: Johnson's bit of a wimp. He'll rarely throw more than 125 pitches in a game. And after that he won't throw a baseball in anger for another five days. OK, we realise that pitching is harder on the arm than hitting a ball with a racquet, but contrast Johnson's workload with Sampras'. During his championship run at last year's U.S. Open, Pistol Pete hit an average of 158 serves per match. He played seven singles matches, including the semis and final on consecutive days. Do the math: Over the course of two weeks, Sampras served 1.110 times — more than a month's worth of work for Johnson.

Reaction Time: Andre Agassi vs Barry Bonds. It's a clich�: Hitting a baseball is the toughest thing in sports. But a case can be made that Bonds and Agassi have more in common than shiny domes. According to Howard Brody, Emeritus professor of physics at the University of Pennsylvania, a 95-m.p.h. fastball reaches the plate in about four-tenths of a second, while a 130-m.p.h. serve reaches the baseline in a half a second. So the necessary reaction time is pretty similar. What isn't similar is the response time needed to hit the moving object. Bonds stands in one spot when he's swinging, while Agassi has to move to the ball. Of course, unlike a pitch, a serve bounces, and Bonds has to make contact with a thin stick of wood as opposed to a 10-square-inch head. But Agassi wins the battle of geometry: He defends a 13 �-foot-wide service box, whereas Bonds covers a 17-inch-wide dish.

Speed: Serena Williams vs Marion Jones: Williams is a lot of things, but faster than Jones? Uh, no. Speed on a court, though, isn't the same as speed on a track. In tennis, you pivot in a microsecond, run hard, and then stop on a dime and shuffle back into position. "Imagine running two miles, but you're doing it in five-yard sprints with direction changes in between, says Paul Roetert, managing director of USA Tennis High Performance for the USTA.

Endurance: Andy Roddick vs Kobe Bryant: NBA players are among the world's best-conditioned athletes. And there's no denying that Bryant is in great shape. But he's got four other guys helping him excel. Roddick? He's on his own. An NBA game has 48 minutes of action, while a five-set match can take five hours. And Bryant plays every game in a controlled environment — it's never too hot, never too cold. Tennis players have to adapt to playing outdoors, indoors, and in cold weather and extreme heat.

Mental Toughness: Jennifer Capriati vs Lennox Lewis: This may be no contest. After all, Lewis kept his cool when he climbed in the ring with the Hannibal Lecter of boxing, Mike Tyson. But here's more food for thought. Both boxing and tennis are individual sports; it's one-on-one with nowhere to hide. But when Lewis goes back to his corner between rounds, he's got a trainer peppering him with advice. On changeovers, all Capriati's got is a towel, a cold drink, and whatever doubts may be rattling around in her head. And last but not least, in tennis there's no clock. If Capriati gets tired while she's ahead, she can't dance through the last few games to close out a match. — Allen St. John