MIKE PERRY, a 31-year-old rower, trained by himself in Ann Arbor, Mich., for six years while his wife attended medical school. Now he is a member of the United States rowing team and hopes to be selected in a couple of months to compete in the Summer Olympic Games.

These days, he works with a coach and a team, and for the first time he is also going to a gym twice a week and lifting free weights for his upper and lower body, and doing a lot of core exercises, he said. His coach insists upon it. Mr. Perry, though, said he cannot tell whether weight lifting is...