WASHINGTON — Cancel the cozy days at Camp David, Md. Put away the underused running shoes. When it comes to weekend enjoyment, all President Bush seems to need is some winding trails and a helmet.

And his mountain bike.

Bush recently has been logging scores of miles on a secluded spread in Beltsville, Md., and the rolling hills of Quantico, Va., far from the White House.

"He's become a biking maniac," said Mark McKinnon, his media adviser and frequent cycling companion.

What began as a way for the president to stay fit, after three decades of running ruined his knees, is now his passion.

Besides burning calories at a 1,000-per-hour clip, cycling gives Bush an emotional rush that sometimes surpasses the one he got from running.

"He's obsessed with it," McKinnon said. "He now likes to do nothing but work out on his bike, and he does it with a frenzy that is reserved for people like Lance Armstrong."

Bush's face lights up at the mention of biking, a heart-thumping release from the stress of his job.

"Prayer and exercise are what keeps me going," he told a Great Falls, Mont., man who asked what brand of bicycle he rides.

His penchant for the messy, sometimes-dangerous sport captured media attention when he took a face-battering spill from his Trek bicycle — reportedly a $3,100 carbon-frame model — while riding it through the hills of his Crawford, Texas, ranch last year.

"We got thrills, spills — you name it," Bush quipped to an Associated Press reporter who accompanied him on a ride during which the president sailed over his handlebars, crashed to the ground, and then promptly hopped back on his bike.

For Secret Service agents and others who have ridden with Bush, it can be a perilous experience. At least one agent has broken several bones trailing the president.

It also can be demoralizing — he is famous for leaving stragglers behind — but seldom boring.

Bush isn't the first to slip a workout into a demanding presidential schedule.

Harry Truman favored brisk, early morning walks. Herbert Hoover tossed a 10-pound medicine ball with Cabinet members. Jimmy Carter and most of his successors were avid joggers — as was Bush, until doctors advised him last year to quit.

But perhaps no president since Teddy Roosevelt, who combined harrowing horseback rides in Rock Creek Park with subzero skinny-dips, has relished so risky a hobby.

That may be why Bush likes it.