In January 2005, the U.S. government released a new set of dietary guidelines essentially telling us that as Americans get bigger, so does the length of time we need to be physically active.

While it's a little more involved than that, the guidelines from the Department of Agriculture and the Department of Health and Human Services indicate that at least 30 minutes of daily physical activity is required to reduce the risk of chronic diseases in adulthood. And for some, that's only the beginn...