Grenoble, France ? For Lance Armstrong and his Tour de France challengers, the true test begins now – in the thin air of the Alps, on snaking climbs lined by screaming fans.

“The mountains put everyone back in their place,” Armstrong’s team manager, Johan Bruyneel, said Monday as the 175 riders left after week one of the three-week race enjoyed their first rest day. “I can’t wait to see what will happen.”

Only by keeping rivals at bay on the relentlessly long and steep ascents can Armstrong retire at the finish July 24 in Paris with a seventh consecutive victory. And only by taking the fight to the six-time champion can his challengers hope to break his record streak.

Armstrong heads into today’s first Alpine stage from a village near Grenoble to the ski station of Courchevel with a sizable but not invincible lead over his main rivals – Jan Ullrich, Alexandre Vinokourov and Andreas Kloeden of the T-Mobile squad, and Italian Ivan Basso of Team CSC.

“Lance is sitting pretty and licking his lips,” said Basso’s American teammate, Bobby Julich.

To win, challengers must put pressure on Armstrong and his Discovery Channel squad by riding hard in the Alps and in the Pyrenees, which follow at the end of the week. Sitting back and hoping the American suddenly collapses is unlikely to be a winning formula: His bad days at previous Tours have been few and far between.

“If you want to beat Lance, if you want to win this Tour, you have to attack, not just follow,” Team CSC manager Bjarne Riis said.

Texan Lance Armstrong, leader of the Discovery Channel cycling team, trains during a rest day at the Tour de France. Armstrong and the rest of the Tour cyclists took Monday off - but they did do a little training around Grenoble, in the French Alps. The Tour resumes with the 10th stage today between Grenoble and the Alpine resort of Courchevel.

The 119.6-mile route to Courchevel includes two major climbs, including a long uphill finish, that likely will show which of the main riders truly are in top form and start separating pretenders from genuine contenders for the Tour crown.

Today’s 10th stage was meant to start in the city of Grenoble. Instead, it will begin 7.1 miles away in the village of Brignoud to allow a demonstration by farmers angry over wolf attacks on their sheep and cows, Tour organizers announced Monday after meeting livestock rearers.

Riders will be held up for a few minutes. Initially, farmers had planned to block the race. The compromise means the stage will be raced over 112.5 miles, instead of the 119.6 miles originally planned.

Armstrong used the mountains in previous Tours to power away from rivals, putting a grip on the race that he kept to Paris. An exception was 2003 – when he struggled, but still found a way to win and match the then-record of five Tour victories.

There was no ambiguity about his record sixth victory last year. He won all three Alpine stages as well as one of two in the Pyrenees and topped off his domination by taking the final time trial. That left him free to sip champagne in the saddle as he rode into Paris to claim the winner’s yellow jersey.

This year, the Texan appears determined to confound those who wonder whether he is too old or jaded at 33 to win again. He rode to a second-place finish in the opening time trial, building big time gaps over Ullrich, Basso and others.

“That was scary,” Julich said. Such a strong starts shows that “he’s ready to rock some cages in the mountains.”