Gretchen Reynolds, author of The First 20 Minutes: Surprising Science Reveals How We Can Exercise Better, Train Smarter, Live Longer, explains how you can change your life in just twenty minutes a day:

The first 20 minutes of moving around, if someone has been really sedentary, provide most of the health benefits. You get prolonged life, reduced disease risk — all of those things come in in the first 20 minutes of being active.

Two-thirds of Americans get no exercise at all. If one of those people gets up and moves around for 20 minutes, they are going to get a huge number of health benefits, and everything beyond that 20 minutes is, to some degree, gravy.

That doesn’t mean I’m suggesting people should not exercise more if they want to. You can always do more. But the science shows that if you just do anything, even stand in place 20 minutes, you will be healthier.

I haven’t read Gretchen’s book, but I am putting her philosophy to use in 2012. My advice: start at just five minutes a day and build up to twenty (or more). It might seem like an insurmountable obstacle in the beginning, which is understandable, but you’ll get there with practice…