Spain's Rafael Nadal speaks with Switzerland's Roger Federer during a group photo ahead of the ATP World Tour Finals in London in this November 19, 2010 file photo. [Photo/Agencies]

More physical

"The sport has become a bit tougher. It's much more physical than say 10 years ago," Soderling, who overpowered Federer in the French Open quarterfinals this year and plays Andy Murray in the opening singles at the ATP World Tour finals, told Reuters on Friday.

"It takes a couple of years to build up your body to be able to compete with the style of tennis now.

"I played my first ATP final when I was 18 or 19, but it was tough to cope with the demands week in, week out."

Roddick, who won the 2003 US Open as a 21-year-old but is still to add another Grand Slam title, believes there are several factors involved - one of them being the slower court surfaces which turn matches into wars of attrition.

"I think when I was coming up the conditions were a little faster and you could rely less on your body," the 28-year-old American told Reuters.

"It's a tough ask of an 18- or 19-year-old to play the kind of tennis we have today 40 weeks a year.

"I weigh more than I used to and everyone is now bigger and stronger, making it so much harder for younger players."

Roddick said qualifying for his eighth ATP Finals despite an injury-hit year had been one of his most satisfying achievements but hoped the ATP would help the leading players by agreeing to shorten the calendar.

"I honestly believe the powers that be are working towards giving us at least some relief, even if it's not perfect," he said. "Because it's getting tougher.

"When I first started this whole thing, if you played somebody ranked 70 or 80 you felt pretty comfortable. Now it's anybody's game on a given day."

Reuters