High intensity interval training (HIIT) describes exercise that is characterised by short bursts of vigorous effort followed by periods of rest or low intensity exercise. High intensity interval trainingis an extremely variable mode of exercise with sessions altered by intensity, duration and number of intervals as well as the duration and activity chosen during the rest period. High intensity interval training has been shown to be an effective alternative to traditional endurance training so often used in exercise interventions. It has also been suggested that High intensity interval trainingis more enjoyable than moderate intensity exercise. These findings are important because lack of time and lack of enjoyment are two of the most commonly quoted barriers to regular activity.