There are various versions around. The most popular is interval training, but there are also strength workouts based on doing complex movements to include as many muscle groups as possible, ab workouts consisting of very advanced core exercises and loads of others.
Although it’s a current fad, interval training was developed in the 1930s to help professional athletes improve their speeds. Any type of training which mixes bursts of high intensity with recovery periods can be classed as interval training. At the moment it is being promoted on the basis that it can burn far more fat in less time than straightforward aerobic training. (This is a complete turnaround from the 90s, when we were being told we had to do low intensity aerobic exercise to stay in our “fat burning zone”.) Interval training works on the principle of pushing the body to work as hard as it possibly can, at a level of intensity which means that oxygen supply to the muscles can’t keep up with demand. That’s why the recovery phase is needed, so that the body can “catch up” and get rid of the carbon dioxide which has built up in the blood stream.
Not only can working at this intensity be a strain on the cardiovascular system, it can also lead to injury in untrained individuals. People who don’t do a lot of exercise tend not to have good exercise technique – their posture and movement control is poor, especially when working at high intensity. This means that they will put excessive strain on joints and muscles (particularly if they are overweight) and are therefore at risk of injury.
The problems with exercise technique and control also apply to high intensity strength and core workouts. You should only do complex moves with weights or advanced core exercises if you are an experienced exerciser and have good technique. Otherwise, you will do it badly, won’t get the full benefit and may well injure yourself.
To gain a fitness instructor’s qualification you have to show you understand some basic principles. These include: the importance of proper warm-up and cool-down, appropriate exercise prescription for the person’s fitness levels and abilities, sensible progression of intensity of exercises over time, assessment of whether an exercise is safe and effective and importance of quality of movement. High intensity short workout training throws all of this out the window and has overweight, inexperienced exercisers jumping in at the deep end doing unsuitable exercises in an unstable way with inadequate warm-up and cool-down.
It’s a craze which is making a lot of money at the moment, which is why people who should know better are promoting it. But advanced exercise is only advisable to those who are a healthy weight, are used to physical activity and are looking to challenge themselves further. It’s not for beginners, the overweight and definitely not those whose bodies are recovering from pregnancy and birth.