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.

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Contributing: Associated Press