Rafael Nadal's physical style and recurrent knee injuries have made him, at 23, a poster child for the worries of wear and tear on young bodies. In tennis, he is hardly an anomaly. According to several experts, advances in racket and string technology, increased speed and power, and unforgiving hardcourts are taking a toll from the junior to pro ranks.

"The sport has changed tremendously over the past 20 years," says Gary Windler, an orthopedic surgeon who advises the ATP Tour and sits on the USTA's sports science committee.

"Players swing as hard as they can on a large percentage of shots," says Windler, and often from extreme positions, which puts "abnormal loads on the hip, knee and back."

Windler says two-thirds of the injuries on the men tour are overuse injuries as opposed to sudden or acute injuries.

Many of these are in the lower extremities, not unlike Nadal's knee tendinitis. At least anecdotally, hip injuries seem to be on the rise among pros, says Wildner (the ATP and WTA tours are in the process of putting together a systemized recording process to better track injuries).

Time compression has added to the stress. Veteran psychologist and coach Vic Braden says players have about half the time they had two decades ago to react to the ball in baseline rallies — from four seconds down to two.

Braden's research specifically on Nadal has shown that the Spaniard puts 4-6 Gs of force — on his knees when he runs, stops and hits, more than other top players such as Roger Federer, who Braden measured at 3 Gs.

"When we saw it, we predicted Nadal would have knee problems or possibly hip problems or growing problems," Braden says. "The body is not made to withstand 5Gs of force on the turn."

Graeme Lauriston, who overseas the sports therapy center at the IMG/Bollettieri Academy in Florida and has worked with injured pros such as Taylor Dent and Tommy Haas, agrees that Nadal is "a very aggressive mover on court."

"It looks like he is loading the joints more aggressively," says Lauriston who also sees an increasing number of young athletes in all sports at the academy with overuse injuries.

Rest and treatments like ice and anti-inflammatories can speed recovery for many overuse injuries, experts say.

Strengthening the supporting muscles around the knee and D]eveloping good core stability around the pelvis and abdomen are important to lessen stress. Like a pitcher in baseball, a stable foundation allows use of the limbs in more efficient ways.

Scheduling another variable, especially for a physical players like Nadal.

"Definitely the way he plays, having some time to rest before and after tournaments optimizes the chance that tendons will be asymptomatic so he can play his best," says Anthony Luke, a sports medicine specialist at University of San Francisco.

Changing mechanics is another option. Some players —Maria Sharapova perhaps most noteworthy of late — have shortened service motions due to a shoulder problems.

But convincing world-class athletes to make adjustments in their technique that may or may not prevent injuries down the road is a tough sell, especially when they have achieved a certain measure of success, says Windler.

The downside: Players that consciously or unconsciously compensate for chronic injuries can inflict other problems. In tennis, the classic case is shoulder problem that turns in to an elbow injury because of altered mechanics.

Untreated, tendinitis in the knees can morph into patellar tendinosis, a condition in which scar tissue develops on the back side of the tendon that attaches to the knee cap, says Luke, director of the UC-San Francisco's Human Performance Center. That is more serious since scar tissue takes longer to heal and can result in recurrent injuries.

Luke says Nadal is in such great physical shape he can get away with a little bit of scar tissue and still perform at a very high level. "These injuries," says Luke, "are kind of on a spectrum."

Still, careers can also be cut short, especially with the nearly 11-month tennis season and more tournaments on cement, experts day.

The bottom line: "Any player that's having repetitive overuse injuries needs to look at their training regimen and playing schedule and make adjustments accordingly," says Windler.