Begin facing a line with one foot in front of the line and the other behind it.  Maintain a slight bend in the knees and keep your weight on the balls of your feet.  Moving as quickly as possible, switch the position of your feet.  Be sure to stay off the line and move your arms along with your legs.  When the right leg comes forward, your left arm should swing forward as if performing the running motion.  The opposite occurs when the left leg comes forward.  Maintain control while moving as quickly as possible for the designated time.