Scientists say staring at the computer for hours rather than hoeing the fields means we are all burning fewer calories a day than we did 50 years ago.
Researchers say this has resulted in two thirds of U.S. adults now being overweight or obese.
Fifty years ago, about half of private industry jobs in the U.S. involved some kind of physical activity: things such as farming, mining, construction and manufacturing.
Researchers say that now that number is less than 20 percent.
