They are going down like bowling pins, sprawled out on the courts of the USTA National Tennis Center in various positions. They stick out their backs, their elbows or their ankles for treatment until they hurt so much they have to stick out their hands for a shake of resignation at the net. They are the players of the U.S. Open. And they are in pain.

"I cannot move on the side -- nothing, not at all," said Magnus Norman, the latest victim of the injury rash that has swept through this tournament. "Obviously, it's a shame because I'm playing the best tennis of my life at the moment. I really felt like I had an opportunity today."

Norman had 1997 French Open champion Gustavo Kuerten down a break in the first set of their fourth-round match, but somewhere between the baseline and the net, Norman wrenched his back going for a drop shot. He struggled through a few more games before retiring with Kuerten leading, 7-6 (7-4).

As the fifth-seeded Kuerten moved to the quarterfinals, Norman became the seventh player to retire from the men's draw with an injury, tying a tournament record. That figure does not include top-seeded Pete Sampras, who herniated a disk in his back before the tournament began; last year's finalist, Mark Philippoussis, who had to pull out with ankle and knee injuries; or Slovakia's Karol Kucera, who could not play with an injured wrist.

The often-injured Todd Martin has managed to stay healthy, gutting his way tonight through his fourth-round match against No. 9 Todd Rusedski, 5-7, 0-6, 7-6 (7-3), 6-4, 6-4. Rusedski served for the match in the third set and led 4-1 in the fifth, only to have Martin win 20 of the final 21 points.

"I thought I was done," Martin said.

Two players in the women's draw have retired with injuries, while others struggled during their matches. Mary Joe Fernandez was beating Venus Williams before she strained her thigh at the beginning of the second set. She finished the match but lost, 2-6, 6-2, 6-2. Eighth-seeded Jana Novotna blamed the ankle she sprained earlier this summer for her loss to Anke Huber Friday and Corina Morariu fell ill during her doubles match with Lindsay Davenport today. Anna Kournikova missed the tournament with a stress fracture in her foot.

Former Wimbledon and U.S. Open finalist Cedric Pioline, who is unseeded, also advanced today. His 6-4, 7-5, 6-3 upset of No. 14 Tommy Haas was without medical incident, although Pioline witnessed the phenomenon first-hand earlier when two-time defending champion Patrick Rafter retired from their first-round match with a shoulder injury.

"It's always a long season and this is the last part of the season," Pioline said. "The hard courts in the United States are usually very hot, and we are playing since three or four weeks ago. We get tired, and it's a difficult surface for everyone."

Several players say they believe the injuries are due to more than just the conditions. French Open finalist Andrei Medvedev blasted the ATP Tour schedule after he lost to No. 2 seed Yevgeny Kafelnikov on Monday, saying the constant travel puts too much wear and tear on the players' bodies.

Right now, players compete on the hard courts of Australia, Europe and the United States from January through March and then switch to the clay-court season, which runs through the French Open in June. After a short grass-court season, culminating at Wimbledon in early July, it's back to the hard courts through the U.S. Open. In the fall, many players participate in the indoor tournaments held all over the globe. "I would much rather see the ATP Tour be broken into two parts," Medvedev said. "I think it's necessary to have a break of, let's say, three weeks, right in the middle of the season.

"The season is just too hard. We are changing balls, changing surfaces. The guys are fitter to be sure, but there are no Supermens. Everybody gets injured, even the most fittest players."

While Medvedev thinks breaking up the season would be the smartest way for the Tour to protect its players, he is not waiting around for it to happen. Each event already scheduled churns out money for the tour, its sponsors and the individual sites, and he said he doesn't believe anyone will agree to anything that would cut revenue.

"I can tell you, it's not going to happen while I'm playing because there is so much money involved," he said. "If you ask me, the tennis will go down this way, because there is so [many tournaments.] The players become like robots. There is not enough emotions, there is not enough heart in the game. Maybe that's what will hurt tennis in the long run, and that's what's hurting tennis right now."

But not everyone agrees. Sampras, who had been hoping to earn a record 13th Grand Slam title here, said many of the injuries -- such as his -- are flukes, not the culmination of too much stress on players' bodies. Sampras tore a small area of cartilage in his lower back when returning a serve in a practice session the weekend before the Open began.

"I've only played 10 tournaments this year, so I haven't overplayed," Sampras said, noting that players get to decide for themselves which tournaments they play each year. "When you play a lot and for many years, you're just going to have some different injuries. Injuries are a part of sports."

U.S. Open

When: Through Sunday.

Where: USTA National Tennis Center, Flushing Meadows, N.Y.

TV: USA network, 11 a.m., 7:30 p.m.

Defending champions: Patrick Rafter, Lindsay Davenport.

Top seeds: Pete Sampras, Martina Hingis.

Yesterday's results: Men -- Gustavo Kuerten (5), Brazil, def. Magnus Norman, Sweden, 7-6 (7-4), retired; Cedric Pioline, France, def. Tommy Haas (14), Germany, 6-4, 7-5, 6-3. Todd Martin, United States, def. Greg Rusedski, Britain, 5-7, 0-6, 7-6 (7-3), 6-4, 6-4. Women's quarterfinals -- Martina Hingis (1), Switzerland, def. Anke Huber, Germany, 6-2, 6-0. Venus Williams, United States, def. Barbara Schett, Austria, 6-4, 6-3.

Today's featured matches:

Men's quarterfinals -- Yevgeny Kafelnikov, Russia, (3) vs. Richard Krajicek, Netherlands (12); Andre Agassi, United States (2) vs, Nicolas Escude, France. Women's quarterfinals -- Monica Seles, United States (4) vs. Serena Williams, United States (7); Lindsay Davenport, United States (2) vs. Mary Pierce, France, (5).