Though running is a great way to build fitness, going from couch potato to marathoner in 60 seconds or less is an excellent way to burn out or injure yourself. Better instead to do some research and find out how to ease your way into training and build up your time and endurance each week. Complete running has an excellent list of the top 10 questions beginning runners ask, including a training chart based on alternating walking and running to build fitness. Whether your dream is to run a 5K, 10K, a marathon, or just making it around the block, they've got all the answers you need.