WSJ states:

The Australian study offers a different take. “It’s not the sweaty type of exercise we’re losing,” says David Dunstan, a researcher at Baker IDI Heart and Diabetes Institute, Melbourne, who led the study. “It’s the incidental moving around, walking around, standing up and utilizing muscles that [doesn't happen] when we’re plunked on a couch in front of a television.” Indeed, participants in the study reported getting between 30 and 45 minutes of exercise a day, on average.