Endurance, the amount of time you can stay active, is a big part of staying in shape. Building your endurance by working out and pushing yourself can put you on a path to health and fitness for the future. Cardio training--whether running, biking, or swimming--is one of the best ways to build endurance and get a great workout. Learn about safety during cardio workouts, as well as how you can make a plan for cardio training--and stick to it!