T.J. Davenport pulls his way to the top of a 100-foot oak during a recreational tree climbing course at Camp Wyman in Eureka, Mo., last month. Such climbs offer good full-body workouts, advocates say.

What's Your Workout: Tree Climbing Ann Koenig is an urban forester for the Missouri Department of Conservation. In her downtime, she's up in the trees -- as a competitive tree climber.

On a hillock on the campus of Xiamen University, a large eucalyptus tree towers above the bamboo grove. A group of men and one woman look up at the maze of silver branches high above their heads. The ...