CRAWFORD, Texas — The most powerful man in the world is also a heck of a mountain bike rider.

And that has nothing to do with the fact that he's followed on his rides by a military attache with the secret codes for unleashing nuclear Armageddon.

George Bush invited me and a few other reporters for a mountain bike ride on his 1,600-acre ranch Saturday. His escapades on the bike have been well-documented: an over-the-handlebars crash here at the ranch and a wet-pavement wipeout in Scotland that hurt a pedestrian policeman.

But the truth about this 59-year-old mountain biker is that the man can really ride. Over the course of a two-hour Tour de Crawford, Bush humbled every rider in Peloton One with a strong and steady pace over hot paved roads, muddy creek crossings, energy-sapping tall grass and steep climbs on loose and crumbling rock.

"This is not a race," he insisted at the start of the ride. "This is a chance for me to show you a little slice of heaven, as far as I'm concerned. You know, some guys go on their ranch and ride horses — I like to ride my ranch on a mountain bike."

But there is one rule: don't pass the president.

No problem. Keeping up with Bush — whose fitness level was recently rated in his annual physical as being in the top 1 percent of men 55 to 59 — was as difficult as any race I've entered.

I started out riding next to him at the beginning of the ride, but when we left the dirt trails and hit the rolling asphalt the pace accelerated to more than 20 mph, which is pretty good for road bikes but absolutely blazing for heavier, knobby-tired mountain bikes. And did I mention that the only factor mitigating the mid-80s temperatures was a very strong headwind?

"I like speed," says Bush, who wore a red-white-and blue helmet and a Western-style bike jersey, complete with pearl snap buttons. His loose-fitting black shorts bore small rips from his crash in Scotland. "There's something exhilarating about heading down a hill at 35 mph on a mountain bike — or trying to grind up a hill at 9 mph."

The president does prefer the speed zones to the technically difficult traverses up and over loose limestone and mud, but his abilities in that area are increasing rapidly.

He began riding just two years ago when a knee injury ended his running routine, but his skills already are quite advanced.

"I love the outdoors," he says, straddling his $3,000 Trek Fuel bike. "If I'm not exercising here, I'll be fishing over there. If I'm not fishing, I'll be working with the chainsaw. I really enjoy being outside, and mountain biking is a way for me to spend a fair amount of time — four or five days a week — outdoors.

"I love exercise. Prior to learning about mountain biking, I was a jogger. And then, like a lot of baby boomers, my knees gave out. I believe that mountain biking is going to be an outlet for a lot of people my age. I'm 59, and people are going to realize you get as much aerobic exercise — if not more — on the mountain bike without being hobbled."

His observation is borne out by the experts. According to Freddie Fu of the University of Pittsburgh Center for Sports Medicine, one of the nation's leading orthopedic surgeons, boomers are suffering knee and other leg injuries brought on by years of pounding the pavement. Fu recommends that they take up soft-contact sports, such as cycling. Fu even sponsors his own cycling team.

"Riding a bicycle gives the cardiovascular benefits of running without the impact," Fu says.

Chris Carmichael, who coached Lance Armstrong to seven Tour de France wins, says the president is doing the right thing.

"He's a shining example of the benefits of having an active lifestyle," Carmichael says. "If you stay fit for all of your life, you can switch sports and also maintain a high level of performance."

Carmichael is familiar with the trend: more than half of the athletes who use his online coaching service are age 40 or older.

"The president is wise to emphasize his aerobic training: Heart disease is the leading killer of American men. That should come before resistance (weight) training."

Bush's physical exam also showed that mountain biking has been beneficial for him in several areas. His resting heart rate was 47 beats a minute — the adult male average is about 68, and pro racer Armstrong clocks in at 32.

During the Saturday ride, Bush's heart rate will average 139 beats a minute, with a maximum of 177 on one of the hill climbs. He will burn about 1,500 calories — enough to erase a McDonald's Big Mac, large fries, milk shake and apple pie.

But you won't find those items on his personal menu. He weighs 191.6 pounds, 8 pounds less than a year ago. His body fat percentage is 15.79, down from 18.25 and well below the "normal" range of 16.5-to-20.5 for his age group.

"Baby boomers who were exercise folks are beginning to realize that there's got to be a better way to get exercise than running, because we are pounding ourselves," the president says. "And I'm hurt — not terribly, I don't limp — my right knee. The doctor said, 'I can fix it for you, and then you can run again. And then I'll replace it.' And I would rather not, at the age of 60, have a knee replacement."

The president recently began using so-called "clipless pedals" that attach a rider's bike shoes to the pedals with a mechanical system similar to ski bindings. The downside is a steep learning curve that can be brutal when the rider can't release out of the pedals.

"They told me that I could be 15 percent more efficient with them," he said. "I was a little nervous at first — you know, kind of being stuck to the pedals made me worried, since I had fallen before."

Despite the seemingly flat Central Texas terrain, he took Peloton One on a very scenic route that included a secluded waterfall and eight creek crossings. He seemed to take particular delight in announcing his pet names for each spot.

Achilles Hill, for example, is a rugged ascent where he once crashed and gashed the back of his ankle on his bike's chain rings.

Balkan Hill, another climb on Saturday's route, got its name because, "That's where Condi Rice gave me and Laura a lecture on the history of the Balkans."

The president acknowledged that there are those who feel his time should be spent on more pressing issues. A few miles from where we rode, peace activists were demanding that he speak with Cindy Sheehan, whose son was killed in the Iraq war.

"I think it's important for me to be thoughtful and sensitive to those who have got something to say," he says. "But it's also important for me to go on with my life, to keep a balanced life.

"The people want the president to be in a position to make good, crisp decisions and to stay healthy. And part of my being is to be outside exercising . . . ."

Armstrong told ABC's "This Week" on Sunday that he'll travel to Crawford Saturday to ride mountain bikes with the president.

Contributing: Associated Press