The Australian men's road cycling team felt the full sapping effect of Beijing's humidity and smog as they trained on the Olympic course.

Cadel Evans, Stuart O'Grady, Michael Rogers, Simon Gerrans and Matt Lloyd did four laps of the tough 23.8km loop at the Great Wall, north west of Beijing, which forms the critical part of Saturday's 245km men's road race.

A thick haze hung over the finish line area and the conditions were muggy.

The day one event could yield Australia's 400th Olympic medal and the Australian Olympic Committee will also watching closely to see what effect the weather conditions have on competitors in such a gruelling event.

The race starts in Beijing and travels about 80km before the hilly loop, which the men must complete seven times.

"You make an effort and you really pay for it in your breathing - when you make a 100 per cent effort, you pay for it," O'Grady said.

"Your body is drained really quickly.

"You're sweating incredible amounts. I've been in probably more humid conditions than this, but just the heat and smog all mixed up, it makes it pretty difficult."

O'Grady said the loop was straightforward, but race tactics would have to be executed carefully.

"It's a pretty hard course, it's going to be draining, the climb is about a half hour in length, it's not a really exciting, technical course, that's for sure," he said.

"It's pretty straightforward - quite a hard, long, drawn-out uphill and just a big, long (descent) down the highway to the finish.

"It's going to be a bit weird.

"It's going to suit most of our riders, but we're just going to have to be smart, it's a bit into the unknown."

Evans was only confirmed for the Olympic team only on Monday, after the knee injury he suffered when he slipped at a post-Tour de France party.

He also did four laps of the course and reported no ill effects.

Asked how he felt after finishing second in the Tour last month for the second year in a row, Evans replied: "It's the stupid knee injury that's been causing me a fair bit of stress lately.

"No worries, no worries - it's going to be seven laps on Saturday, it's going to be a different story."