The Fit Runner: Episode 1 - core training Sep 16, 2011 is proud to introduce you to the "The Fit Runner," a new series. The first episode, which covers core training. These workouts will apply to you whether you are already on an elite level or just beginning. For beginners they may serve as an intense workout to build your core muscles. If you're already in shape they are crucial for you to maintain and sharpen that core strength, maximize performance, and to prevent injury by helping you stabilize your movement.