PARIS -- Justine Henin-Hardenne, all of 57 kilograms soaking wet, plays a big game. It's only when she reaches the semifinals of the Grand Slam events, that her diminutive size -- 5-foot-5, 126 pounds in U.S. currency -- leaves her vulnerable.

	Justine Henin-Hardenne is working at putting on muscle.

And that is where the No. 4 seed finds herself after handling Chanda Rubin 6-3, 6-2 in Tuesday's quarterfinal match.

Lurking in Thursday's semi is top-seeded Serena Williams, who is listed at 5-8, 130 pounds but is, by consensus, closer to 160. Even if Henin-Hardenne manages to win, she would probably face No. 2 seed Kim Clijsters, a fellow Belgian who goes 5-8 ½, 155 pounds, in the final.

"I know that if I want to play long matches and long rallies with players like that, I need that muscle, so I had to work in that direction," Henin-Hardenne said. "I think it was absolutely pivotal for my game. We are seeing the results since the beginning of the year, but I still need to improve that."

Against the No. 8-seeded Rubin, whose modest frame is similar to Henin-Hardenne's, size did not matter. In a 66-minute match, Rubin never really pressured her.

Henin-Hardenne lost her serve to open the match but won the next four games. Rubin had a chance to get back in the match with Henin-Hardenne serving at 4-2, but a loose forehand (a moonball that sailed long) and an ace that clipped the line down the middle sent Henin-Hardenne on her way.

"I was a little bit nervous this morning," she said. "When I finally got on the court, I said, 'OK, just play point after point.' I think I played pretty well today, especially on important points. I played a lot with my forehand. It's true that it became the best shot in my game for sure. My serve, I was pretty happy. If you play only with your second serve, you can't be aggressive enough to beat them."

Said Rubin: "I've beaten her before. We've had some tough matches where I haven't won. Maybe this surface she prefers, but I felt like I had a really good chance, just a few times where if I had just been a little more solid, I think it would have been a different story."

Henin, who celebrated her 21st birthday on Sunday with a victory over Patty Schnyder, has been all over the Grand Slams for the past three years. She broke through with a semifinal appearance at Roland Garros in 2001, then reached the final at Wimbledon three weeks later. Last year it was the quarterfinals in Australia and the semis at Wimbledon. This year she lost to Venus Williams -- all 6-1, 160 pounds of her -- in the semifinals of the Australian Open.

Since then, she's won three tournaments -- Dubai, Charleston and Berlin -- and accrued confidence along the way.

In Charleston, she ended Serena Williams' 21-match winning streak with a 6-3, 6-3 victory. It was her first win ever over a player ranked No. 1.

Rubin doesn't think it will happen again.

"Serena's looking really tough, and she obviously wants it again this year," Rubin said. "That's the biggest thing on clay, I mean, who wants it the most and who's willing to pay the price.

"I think if you're a betting person, you'd have to bet on her again."

Greg Garber is a senior writer for ESPN.com.