 What is interval training? Interval training is a controlled period of intense max effort running followed by a recovery or an interval which is then repeated. You can measure your interval by time or distance or a mixture of the two. So you might do 800 meters hard effort with a 200 meter recovery or you might do one minute of hard effort and one minute interval. You could also do 400 meters at hard effort with a one minute interval. These hard efforts need to be in zones four or five of your heart rate that's almost anaerobic effort. Running fast intervals helps to increase your VO2 max and that's the amount of oxygen that your blood cells can store. The more oxygen your blood cells can store the more is available to your muscles to run quickly. Interval training was popularized by Emil Zatopec in the 1950s. He did almost exclusively interval training however I want you to do intervals once or twice a week and no more.