Researchers at the Mayo Clinic have built what they called a 'vertical workstation', a desk fitted over a standard treadmill.

The researchers report online in the British Journal of Sports Medicine how they persuaded 15 obese people to work at this treadmill-desk, then measured how many calories they burned.

Professor James Levine and Jennifer Miller found that on average their volunteers burned over 100 calories more every hour while walking slowly, at 1.6 kilometre per hour, than while sitting in a chair.

"If obese individuals were to replace time spent sitting at the computer with walking computer time by 2 to 3 hours a day, and if other components of energy balance were constant, a weight loss of 20 to 30 kilograms a year could occur," the researchers write.