As for the idea that the tendency to sit still might be genetic, he said that no "lazy genes" had been identified and added, "I personally believe in self-determination over detrimental biological predisposition."

Dr. Jules Hirsch, an obesity researcher at Rockefeller University, said studies in the 1950s first suggested that obese people were less fidgety than thin ones. One study, of young women playing tennis, showed that although fat and thin ones played equally well, fat ones wasted less motion hitting the ball. They were seemingly more efficient, and probably burned fewer calories.

Hirsch said some people were probably born with, or developed at an early age, a "greater efficiency at caloric storage," from eating more or moving less.

"This phenomenon helps store energy but is a great risk factor for the development of obesity," he said. But until it is understood better, he said, "we're not apt to understand the overall obesity problem any better."

Levine of the Mayo Clinic said that the study findings had inspired him to redesign his office. His computer is now mounted over a treadmill, and he walks 0.7 miles an hour while he works.

"I converted a completely sedentary job to a mobile one," he said.

The walking is addictive and "terribly good fun," he said, adding that he has had 30 or 40 requests from colleagues at Mayo for treadmill desks like his.

Has he lost weight? He does not know.

"I'm a relatively lean bloke," he said. "I never weigh myself. You'll think I'm a bad nutritionist. I don't recommend people weigh themselves all the time. It's not a healthy thing to do."