Interval training is a method of increase running speed by running repeat sets within a given time frame, taking a recovery jog between each set. Use interval training to prepare for a short race or even a marathon with tips from a running coach and certified sports trainer in this free video on running. Expert: Samuel Harvell Bio: Samuel Harvell is certified through the National Endurance Sports Trainers Association (NESTA) and is an experienced running coach. Filmmaker: Bing Hu