Andy Murray has been burned so often on the issue of drugs in tennis that he is understandably wary of offering too strong an opinion each time the subject comes up.

While preparing for tomorrow's third-round match with Ricardas Berankis of Lithuania at the Australian Open, Murray was planning to watch Lance Armstrong's interview-come- confessional on the Oprah Winfrey Show, as were many players here.

While doping has publicly ripped through cycling over the years, tennis has had only a few high-profile cases of players failing tests.

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Murray's opinion, for what it's worth, is that the sport is largely clean but that improved testing can only be a good thing. "I discussed it at the end of last year and I don't want to get into it again because it caused more questions," Murray said. "But all sports will take note of what has been said and what has happened and improve their doping controls."

Last October, when asked the question at the Paris Masters, Murray said he thought anti-doping was improving but that there should be more blood testing, especially out of competition.

The topic of drugs was rehashed by Australian papers this week, citing comments from the former Belgian player Christophe Rochus that he originally made more than two years ago. Rochus, one of the shortest players on the Tour, said in 2010 that "it is inconceivable to be able to play five hours in the blazing sun one day and still run like a rabbit the next day".

In a Belgian newspaper this week, Rochus repeated his 2010 claims that the ATP, which runs the men's game, wrote to him warning him not to make such allegations, saying he "had no evidence".

Yesterday, Murray said he thought Rochus's "rabbit" allegations were wide of the mark. "I would say that is far from the truth," he said. "Anyone can see the number of hours of training and amount of practice that go into what we do and there are other sports that are far more challenging, endurance-wise, than tennis.

"The guys can't play five or six hours and then come back the next day and run around like a rabbit. When guys play five or six hours in the slams like we often do, we have a day's rest. I was told that after our [semi-final] match last year here, that on the day off, Novak [Djokovic] didn't practise, didn't hit a ball, didn't get out of bed till 3pm."

"Providing you put the work in it doesn't mean it hurts any less when you have to play a couple of days later after a five-hour match, but I would not say it is impossible."

Watching Murray destroy the challenge of Joao Sousa in the searing heat – temperatures peaked at 40.4°C, it was easy to forget that it has taken years of training on and off the court for him to get to his level of fitness.

It has been said that he and Djokovic have taken the sport up another level, no mean feat given the efforts of Rafa Nadal in recent years.

"Rafa was the first one to have that physique that looked like a true world-class athlete across any sport," Murray said. "Tennis players are always in good shape but I think he looked like he could do any sport. The game has changed physically, it's much more demanding, and I have adapted my preparation and training, reducing the number of tournaments I play.

"Spending more time preparing and getting myself ready for events is the best way to prepare. Still not everybody does that, but I believe that's the best way."

As a junior world No.1 in 2007, Berankis was tipped to make it big in the men's game but a series of injuries interrupted his path toward the top. Now fully fit, he is set to break into the top 100 after this tournament and he and Murray know each other well, having practised together on many occasions, including in Brisbane a fortnight before Melbourne.

Murray said Berankis was "a nice guy" and said he is happy to see him doing well but said it was no surprise young players were taking longer to make it these days.

"The average age of the top 100 is 28," Murray said. "I would guess that is a couple of years older than five years ago. The game is changing; it takes guys longer to physically and mentally cope.

"You have to develop mentally much quicker to understand and appreciate how much the game is changing. It will for sure take guys longer to break through unless you get someone who is an incredibly gifted and talented athlete."

Roger Federer cruised past Nikolay Davydenko in straight sets and Juan Martin Del Potro crushed Benjamin Becker while in Murray's eighth of the draw, Gilles Simon and Gael Monfils set up an all- French clash. Monfils served four wild double faults on consecutive match points before finally closing out his match with Lu Yen-Hsun of Taiwan.