Yep, it is a DAY, thus the 23 1/2 hours. Thanks for pointing that out. In the study he mentions that... Lack of exercise or low fitness is the strongest predictor of death.

So now, think about how we can all utilize our time in the ATL airport to get that 30 minutes of walking in... skip the Plane Train, and even that Porsche ride! OK - Take the Porsche ride but be sure to walk later.