Exercise fads are big in America. We love the novelty of hot yoga one minute and Zumba the next.  The whole industry has evolved so much over the last 70 years when presidents Eisenhower and Kennedy made physical fitness a spoken priority.  In truth, however, only 20 percent of Americans exercise regularly and America seems to the naked eye to be overwhelmed with the issue of obesity in both children and adults.  So how is it that each New Year more people resolve to get in shape but so few do?  In some sense the pressures of everyday life get in the way for many people just trying to keep basic family responsibilities together with little time for anything else; while others have no access to gyms, good recreational areas or even enough room in their homes in which to put a treadmill.  It’s a fascinating history as to how we got here and it is brilliantly documented in “Fit Nation: The Gains and Pains of America’s Exercise Obsession” by our guest, Natalia Mehlman Petrzela.  I share my workout history.  That alone is a reason to listen in.  It may surprise you.