* Nadal moves well as he hammers Federer
* Says he is surprised by early results (Writes through after Nadal beats Federer)
INDIAN WELLS, California, March 14 (Reuters) - Rafa Nadal might reflect fondly on days when post-match chatter was of shot-making and title-runs. These days it consists mainly of arthroscopes and surgeons.
The Spaniard, then, must be mightily satisfied his left knee -- the most scrutinized body part in men's tennis -- passed a high profile examination on Thursday when he swept aside great rival Roger Federer to reach the semi-finals in Indian Wells.
The attention foisted on Nadal at the BNP Paribas Open this year, his first hardcourt tournament in almost a year, has been extraordinary, even for a man who has been one of the biggest names in the game for almost a decade.
Though the left-hander has made a noteworthy return to his favoured clay courts in recent weeks, the hard courts of Indian Wells were always likely to provide his toughest test on a surface where his counter-punching style has often been least effective.
Following a second-round exit at Wimbledon last year, Nadal was sidelined for seven months by an injury to that knee. The tennis world has closely monitored his recovery and progress ever since.
The 26-year-old has progressed smoothly at Indian Wells, though, winning his first two matches with one walkover before thumping long-time rival Federer 6-2 6-4 in the quarters.
He has shown no visible signs of discomfort, with the knee taped throughout his matches, and said he was especially pleased with his movement while taking advantage of Federer who was struggling with his own back niggle.
"My movement tonight was much better than yesterday," 11-times grand slam singles champion Nadal told reporters.
"I played longer than yesterday. I played a fantastic first set, in my opinion.
"Sometimes I am not able to play all the shots with my forehand that I used to because I am not that fast yet to do it. That's why the backhand today is very important for my game.
"But it is a big surprise for me to have these results, that's the truth ... because I really was not able to practise a lot. I was able to practise just a little before the comeback."
While world number five Nadal has eclipsed his own modest expectations at Indian Wells, his fans and some of his peers remain worried about the prognosis going forward.
Serbian world number one Novak Djokovic, a long-time rival and friend of Nadal, is well aware of the toll paid by the Spaniard because of his ultra-physical playing style.
"He really suffers on the hard courts," the Australian Open champion told Reuters. "He loves to run around the court and do a lot of dynamic strong movements that eventually can hurt him, as they did in the last seven months.
"But being so long off the tour, I'm sure that he has taken his time and has been very patient ... and now it has resulted with a great comeback."
Ross Smith, a keen tennis fan and perennial visitor to the Indian Wells event, encapsulated what many Nadal fans fear.
"It does concern me, especially what we have heard about his knee injury and how long he has been off," he told Reuters. "You kind of think, 'How long can this guy last playing this kind of tennis?' I don't think he's going to be able to keep it up personally. He's 26 and it's just that impact on his knee with all his rigorous tennis.
"It's just insane for these athletes to continue performing at that top level during a long tennis season, and especially the way that Rafa plays."
It certainly made sense for Nadal to return to the circuit last month on clay. He flourished in South America, competing in three smaller claycourt events -- winning two of them having reached all three finals.
Perhaps no player understands better than Juan Martin Del Potro what Nadal is going through, the towering Argentine having missed eight months in 2010 due to wrist surgery.
While Del Potro has been hugely impressed by the smooth nature of the Spaniard's ATP comeback so far, he believes the mental aspect of Nadal's recovery will be crucial.
"It's very important to be strong mentally," 2009 U.S. Open champion Del Potro told Reuters. "For me, in the end, I was completely recovered from my wrist injury but in my mind it was still there and I couldn't play because when I hit some balls my mind is saying to me, 'You are still injured.'
"And then I would get an MRI or see the doctor and be told that my injury is gone. I don't have anything more in my wrist. But I think Rafa is working very well mentally, he is so strong as he shows in every match."
Del Potro, who played just three tournaments in 2010 because of a lingering injury to his right wrist, said a no-risk strategy would be vital for Nadal to follow closely.
"He has really to be safe with his new problem, and on the hard courts here at Indian Wells that's a matter of how far he is going in this tournament," the 24-year-old from Tandil said.
"The big challenge for him is playing healthy, not feeling any pains and being ready to play tennis again.
"He has this tournament, maybe Miami, and then the clay season comes again so he needs to be smart to play these tournaments, not put his knees at risk. If he is still feeling painful, it's going to be a tough moment for him for sure."
The crowd-pleasing Nadal, who has been given an electrifying welcome by fans so far at Indian Wells, has relished the support but has repeatedly said he does not expect too much too soon on the hardcourt surface.
"I go day by day as I did all my life, and that's not gonna change," the Spaniard said on Thursday.
"If the things are not working well, so change, but if the things are working well don't change, no?
"Important thing is be healthy. And if that happens and I'm able to practise as much as I can, as much as I want, probably the comeback will be a little bit less difficult, no?" (Reporting by Mark Lamport-Stokes; Editing by Frank Pingue/Ossian Shine)