Running in marathons has become so popular in recent years that race organizers in some cities are being forced to limit participants through lottery systems. We look at what it takes physically and mentally to run a marathon, and why the sport is growing.
Dean Karnazes, ultra-marathon runner and author of "RUN! 26.2 Stories of Blisters & Bliss"
Anthony C. Luke, associate professor of clinical orthopaedic surgery at the UCSF School of Medicine, director of the UCSF Human Performance Center (HPC) at the Orthopaedic Institute and founder of the RunSafe injury prevention clinic