Do not even dream of winning both the Giro d'Italia and the Tour de France - unless you are Superman or Alberto Contador.

Contador, Andy Schleck and Lance Armstrong are sitting out this year's Giro, the podium finishers in last year's Tour de France opting to save themselves for the world's greatest stage race.

"Cycling as a whole is much more specific than it was 30 years ago," Garmin-Transitions manager Jonathan Vaughters told Reuters.

"Thirty years ago, all top riders would take part in all the races and it was eventually a competition of endurance. If you do this today, you're up against rivals who are 100 per cent fresh and you can only be mediocre during the entire season.

"Cycling is going the way of other (individual) sports. You don't compete 120 days a year."

Many riders ride the Giro and Tour in the same year but they cannot expect to win both races.

"The only one I can think of is Alberto Contador," said Vaughters.

Twice Tour champion Contador took part in the 2008 Giro -- and won it -- only because his Astana team had been left out of the Tour de France because of their doping record.

Last year, seven-times Tour de France champion Armstrong started the event in his comeback year, but only to prepare for the Tour.

Italian Marco Pantani was the last rider to achieve the Giro-Tour double, in 1998.

"With all the repercussions a Tour victory can have, it is hard for a rider to take the chance to lose out on a Tour title for a Giro win," Astana manager Yvon Sanquer told Reuters.

Fausto Coppi, Jacques Anquetil, Eddy Merckx, Bernard Hinault, Stephen Roche and Miguel Indurain were the only other riders to achieve the Giro-Tour double.

"Only a great champion can do it," said Sanquer. "But it takes a great leader and also a great team to back him on those two races."

With only a month between the end of the Giro and the start of the Tour de France, recuperation is a major problem.

"You can think about it, dream about it but the organisation needs to be perfect," Sanquer explained. "It is extremely demanding, psychologically and physically, more than before."

Russian Denis Menchov went for the double last year. He won the Giro but quickly dropped out of contention in the Tour de France and finished 51st overall.

"Riding a Giro-Tour double is one thing, to win both is another," said Sanquer.

But the Giro remains a great challenge with tough climbs and beautiful surroundings, according to those involved in the three-week race.

"Winning the Giro d'Italia is never easy whatever the group of riders. This year the race won't be lacking in champions even without Contador, Armstrong, Andy Schleck, 2009 winner Menchov," Italian Damiano Cunego told Reuters.

"It's enough to think of world champion Evans, Sastre, Wiggins, Basso, Bruseghin, Garzelli, Scarponi.

"Whoever is at the Giro will still have great motivation and for this reason I believe the level of the race is still very high."

Stay tuned to Roadcycling.com for our complete 2010 Giro d'Italia coverage, which will include video highlights from each stage of the Giro. Also, check out www.universalsports.com/cycling for full video coverage of each stage.

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