High-intensity interval training (HIIT) or sprint interval training is an exersise strategy that is intended to improve performance with short training sessions. HIIT is a form of cardiovascular exersise which is beneficial to burning fat in a short and intense workout. Usual HIIT sessions may vary from 9–20 minutes. The original protocol set a 2:1 ratio for work to recovery periods. For example, a runner would alternate 15–20 seconds of hard sprinting with 10 seconds of jogging or walking.