Caroline Wozniacki pushing it to the limit

NEW YORK -- It was past 9 p.m. on Friday. The U.S. Open was to start Monday. And where were Caroline Wozniacki and Elena Dementieva? Heading deep into the third set of their semifinal at the Pilot Pen Tennis tournament in New Haven, Conn.

Wozniacki was playing her seventh match in 10 days. After a washed-out weekend at the Rogers Cup in Montreal, she completed her semifinal and final matches on Monday before heading to New Haven to begin her title defense Wednesday.

Dementieva was into her eighth hour of play that week. She went more than three hours in both her first two rounds and was about to hit the 2-hour mark in the semifinal.

Any player, knowing that the year's last major was just around the corner, might have concluded that the sensible thing to do was take a few big swings and finish the match quickly one way or another.

Not these two. They slugged it out in long, entertaining but draining rallies. Wozniacki, who was struggling with a stiff back all week, fought back after losing the first set 6-1 and again when Dementieva served for the match at 5-4, challenging a call early in the game to show she was still fighting tooth and nail. Dementieva, in turn, saved triple-match point in her next serve game before finally succumbing in the deciding tiebreaker.

Was it courage or madness? It was hard to decide.

That's not all. After winning her semifinal against Dementieva, Wozniacki returned less than 18 hours later to take the final against Nadia Petrova in three sets. She's clearly playing some of her best tennis, but how much more of it does she have left?

The 20-year-old from Denmark begins her U.S. Open campaign Tuesday against American Chelsey Gullickson, a wild card. Wozniacki is the tournament's top seed thanks to Serena Williams' withdrawal. A finalist last year, Wozniacki will try to win her first Grand Slam title as well as reach No. 1 for the first time. She also will try to do something rather unusual in tennis -- play for four consecutive weeks without being defeated. A day off between matches will help, but a tough draw that includes the likes of Maria Sharapova and Svetlana Kuznetsova in her quarter will not.

John McEnroe gave the age-old topic of scheduling a bit of a buzz factor last week by saying that the women "shouldn't be playing as many events as the men." Around the same time, the WTA Tour released the latest in its series of Roadmap reports, tracking the effect of its overhaul of the schedule at the beginning of last year. Player withdrawals are down 35 percent, the tour reported, and top players are meeting their tournament commitments 84 percent of the time.

Both are something of a red herring: McEnroe's statement because of its provocative phrasing, and the tour's because of the potential semantics involved in the vaguely phrased measurements. More concrete is the litany of injuries the top names have suffered at some point during the past year.

What's more, the average number of tournaments played by the top 10 currently stands at 19, not appreciably different from the past five years. The average number for the top 50 is 22, again similar to the past five years.

But it is noticeably different from 1996, the last year the WTA had rankings that took the average of a player's ranking points per tournament rather than adding up her best results. That year, both the top 10 and top 50 played an average of only 17 events. And by all accounts, the power and physical impact of the game has increased significantly since then, with a resulting increase in wear and tear.

"Women's tennis has become so intense and powerful and strong, and I think obviously we also have to work harder outside of what we do on the tennis court," said defending U.S. Open champ Kim Clijsters, who returned to the tour last season after a two-year retirement. "We did running, but now it's the little details. Every little detail makes a difference, and I think we have to become fitter, faster, stronger."

At the same time, having the big names present at the big events is vital for maintaining the sport's profile and the prize-money increases that tournaments promised in return for better fields under the Roadmap.

The Roadmap has reduced the number of events that top players are required to play but gives players less choice about when and where to play. Some players, including Wozniacki and Victoria Azarenka, have publicly said they have played while injured this season to avoid the fines and penalties imposed for missing tournaments.

Tour rules do not require players to play hurt, only to show up at certain events and do some publicity to avoid fines. But not playing does cost the big names a share of their bonus-pool money at the end of the year.

Clijsters, who played a heavy schedule during the first edition of her career but is now much more selective because of her commitments to her 2-year-old daughter, Jada, likes the new structure. "I have to say the new system is a lot more player-friendly," she said. "You don't have to play every week but give yourself 100 percent when you can be out there."

She wants her colleagues to take more responsibility for their schedules. "It's a player's discipline and professionalism to know when to play or how many tournaments am I able to play," Clijsters added. "I think that's something that is really important, is listening to yourself and not worrying a lot of times about points or about money. Because in the long run, if you're fresh, all those things will get there, and you'll play better and your points will come."

Working out a sensible plan and managing one's body correctly are the keys to getting through the season in one piece, says Mark Wellington, a trainer who has worked with Sharapova and Azarenka in the past.

"The biggest problem in women's tennis at the moment is that people don't schedule their year right -- everybody's chasing points, everybody's chasing a few dollars," he said in an interview earlier this month. "It's not rocket science, but it is a science, you know, and it does need work.

"More of these girls need to listen to their team and get good trainers and do the schedule fitting in rest weeks, training weeks and recovery weeks in with the tournaments.

"With the correct training program it is very possible to get through the whole season unhurt.

"If they really believe they can win Grand Slams and they're really big players, you don't have to play 30 events a year. You peak three or four times a year, you go deep in the big ones."

Playing with injuries is a recipe for trouble, he added. "I think it's very naive to play with injuries, because there's very few injuries that can't be fixed if you just take the right time off," Wellington said.

"Look at [Dinara] Safina last year, she was chasing the No. 1 ranking in the world, and she almost crippled herself doing it. She had a back problem in the middle of the year, but she carried on playing because she was determined to be No. 1. And is it worth it? She sat out earlier in the year, and now she's free-falling at the moment."

When Azarenka injured her knee by catching it in a hole on a clay court before the French Open last year, Wellington advocated cutting back on practice time.

"I told Antonio [Van Grichen], the coach, that she can barely hit every day and we can play [the tournament]. He trusted me, and Victoria wasn't happy with it, but we literally did 10-15 minutes every day until she played," Wellington said. "Then she made quarterfinals [and] she made the quarters of Wimbledon a couple of weeks later. She probably would have missed that whole block if she had trained every day before the French Open started."

The top of the game seems increasingly divided into two camps -- players who play as much as they can (e.g., Wozniacki, Jelena Jankovic, Agnieszka Radwanska) and those who play a limited schedule built around the big events (Serena Williams, Henin, Sharapova, Clijsters). Without question, the latter group has been more successful in the Grand Slams and other large tournaments, but it's not clear which comes first. Do they have the luxury of playing selectively because they're capable of winning Grand Slams, or do they win because they focus their energies on preparing for them? The capability is naturally the most important, but the preparation is also a key enabling factor.

Each player is also different -- some need more match play than others -- so there is no one schedule that fits all.

And playing styles are clearly a factor. Ironically, it's the selective players who have suffered freak injuries forcing them to miss Slams -- Serena at the U.S. Open with her foot (although off the court), Henin at the U.S. Open with an elbow injury caused by diving on the court and Clijsters at the French Open after suddenly hurting her foot when planting it during a match. At the same time, those taking part in tournament after tournament often have proved surprisingly resilient, although they lack the biggest trophies.

Wozniacki hopes to change that during the next two weeks, but it's the impact of the past two weeks that could greater illuminate what the limits of competitive endurance are these days.

Kamakshi Tandon is a freelance tennis writer for ESPN.com.