Extreme sports and extreme music are the order of the day in Roztoky u Prahy, when the fourth annual Dirt Jump competition goes off-road and airborne July 31.About 40 riders, divided into two competition categories - mountain bike and BMX - will throw out their best tricks in pursuit of a 15,000 Kč ($765) grand prize.And extreme sports aren't so extreme without the tunes to match, so an array of DJs will entertain before, during and after the competition.

Each year, the experience is always different," said Jan Kolář, aka DJ Tazz, the competition's organizer. "It all depends on the atmosphere created by the audience, having a good announcer, good riders and, of course, the weather."Dirt jumping is the practice of riding bicycles over mounds of dirt or soil with the goal of launching one's self into the air. The key is to launch high enough to perform tricks while airborne - and the more the better. Then, of course, there is the all-important landing.

In Roztoky, competitors in both categories must participate in four qualifying rounds, each consisting of three jumps. "The eight best riders in the qualification rounds go to the final," Kolář said. A panel of judges scores each jump based on precision, difficulty and overall style and impression.

"When all the rides are finished, the scores are added up, and the one with the highest score wins," Kolář said.

Ondřej Mladý won last year's competition in the mountain bike category. At age 14, Mladý changed his hobby from conventional biking with his parents to dirt jumping. That was 10 years ago, and he has no plans to give up the sport anytime soon. Mladý called his 2009 victory "a great competition," but the challenging nature of the sport has taken its toll on the biker, leaving a repeat victory in doubt.

"I have medical problems, so I don't know yet whether I will be able to compete this year," Mladý said. "But I hope to return."

The show takes place at the same location as last year, but the course and the spectator areas have seen some upgrades in the past 12 months. The course, Kolář said, was built five years ago by a group of local riders but is now poised to welcome some of the best riders in the Czech Republic - or, as Kolář said, "Anyone who has courage can take part in the competition."

Kolář clarified his remark, however, perhaps foreseeing a spate of lawsuits in his future: "The track is difficult, and thus only Czech riders who have a lot of experience compete." The conclusion of the day's riding will include a best-trick contest.

Entry to the competition is free. Practice rides begin at 10 a.m., before qualification launches at 1 p.m. The Best Trick Competition is expected to take place around 4 p.m. The after-party kicks off at 6 p.m. at the nearby Tropic Bar, when the day's other stars, the DJs, take center stage.