HIIT or high intensity interval training is time efficient, fun and works great to aid fat loss.
Intervals are rest breaks in-between high intensity exercise, of which the duration can change. In simple terms, you have a work period and a rest period. The ratio of work to rest can change depending on the desired outcome of the training or the fitness level of the participant. For example, a common interval I use with clients gives an equal amount of work to rest, this is a known a 1:1 interval. If I had a client who is in good shape potentially we could go to 2:1 so the work period is twice as long as the rest period. Working twice as long as resting obviously makes it much more intense as you don’t have as much time to recover in-between your working sets.
We could go even further with the interval and make it 3:1, this would be very intense so either the total duration would need to be shorter or with sensible exercise selection we could sustain it for longer.
A typical interval session could last anywhere from 5- 30 minutes, depending on the exercises employed and the desired outcome of the session. There are many different ways to perform intervals and that is why they are a great addition to your training.
HIIT has been shown in studies to burn a higher number of total calories than steady state cardio but only just. 30 mins of HIIT only outguns 60 mins of steady state cardio by around an estimated 200 calories or so. It has the advantage of taking less time but the disadvantage of taxing our nervous system to a higher degree and therefore requires more recovery time in-between training.
I would not recommend more than 3 HIIT sessions per week and steady state cardio still has its place to aid fat loss and should not be counted out.