Paul Rider runs on Mulholland Drive in Los Angeles, March 25, 2011. Researchers say a moderate running regimen is actually beneficial for the joints of people with healthy knees. Dennis J. Provost for NPR hide caption

itoggle caption Dennis J. Provost for NPR

Five-year-old Andy Villatoro plays with a toy he received with a Happy Meal at a San Francisco McDonald's last year. David Paul Morris/Getty Images hide caption

itoggle caption David Paul Morris/Getty Images