High Intensity Interval Training involves brief periods of maximal, or near maximal effort with short rests in between. It is now enormously popular, acting as the basis for gym classes and exercise regimes all around the world. This is a recognition of the that this form of training gives good results with a much lower time commitment than traditional, moderate intensity or steady state training.
Although HIIT has really taken off in the last twenty years, with research into it rising almost exponentially, as a form of training it has been around for about a century and was being used by successful Olympians in the 1920s and 30s. When Roger Bannister ran his sub four-minute mile in 1954, he had actually trained for this by performing sets of 400m runs in under one minute with a two minute break between each one.
But the granddaddy of HIIT is the Tabata, named for Professor Izumi Tabata who undertook a landmark study in 1996. His regime was four minutes of training comprised of 8 X 20 second maximum efforts with 10 seconds rest between each one. He showed that 43 minutes per week of training in this way was more effective than 300 minutes per week of conventional training. HIIT was thus established as the way to incorporate an effective training regime into a busy lifestyle.
In fact, research into HIIT is sometimes divided into low-volume training, which is less than 15 minutes long, and high volume which is longer than 15 minutes. If your HIIT session is much longer than this, you are probably not doing it right.
The plethora of research that has been conducted into HIIT shows that it is good for cardiovascular health, reduces the risk of the metabolic syndrome, improves mood, helps prevent falls in the elderly, reduces the risk of breast and colon cancer, osteoarthritis and low back pain. In short, it is very good for you.
Biologically, HIIT improves your V02 max (the maximum rate at which you can consume oxygen) and improves the metabolic efficiency of muscle fibres by upregulating glycolytic and oxidative energy systems (essentially increasing the speed and efficiency with which the muscles can use their fuel).
Why is it more effective than conventional training?
During prolonged, moderate intensity training, the muscles’ demand for fuel and oxygen can largely be met as the exercise continues. Once the exercise stops, the body returns to a resting state and there is not much need for recovery and not much stimulus for adaptation. During HIIT, the aim is to overwhelm the body’s ability to meet the energy demands of the exercise, both at a cellular level (in the muscles) and at a whole system level (for example the ability of the heart to beat fast and forcefully enough, or the lungs to take in enough air). This overwhelming demand stimulates a whole load of adaptive processes in the body to ensure that the body is better able to cope with such demand in the future.