Begin facing a line with your feet hip width apart and toes behind the line.  Maintain a slight bend in the knees and keep your weight on the balls of your feet.  Begin by stepping forward over the line with one foot and then the other and then stepping back over the line with the lead foot and then the other.  Follow this pattern leading with the same foot for the entire designated time.  Lead with the opposite foot during the next repetition.  Move as quickly as possible while maintaining control and staying off the line.