<human>:  I have a question about High Intensity Interval training. How long should I do HIIT for?
<bot>: HIIT is a form of exercise that involves short bursts of intense exercise followed by short periods of rest. The intervals are usually between 30 seconds and 2 minutes. The length of the intervals depends on the intensity of the exercise and the duration of the rest periods. Generally, the shorter the interval, the more intense the exercise and the longer the rest periods. For example, a 30-second interval with a 30-second rest period would be considered a moderate intensity exercise.