Lance Armstrong announced Thursday that he will not be racing the Leadville Trail 100 mountain-bike race in Colorado.

"Lance had a scheduling conflict come up and he regrettably cannot participate in the event," said Mark Higgins, the seven-time Tour de France champion’s manager.

Armstrong's successor as Tour champion, Floyd Landis, also has expressed interest in racing the Leadville 100. But the event carries a NORBA sanction, which means Landis would not be able to compete should he be suspended for a positive testosterone test at the 2006 Tour, unless organizers decide to proceed without the sanction.

The course starts at over 10,000 feet of elevation and peaks at 12,600 feet. Armstrong’s longtime coach, Chris Carmichael, raced the 2006 edition and finished in 9 hours, 18 minutes.

For more information on the event, see www.leadvilletrail100.com.