HIIT is short for High Intensity Interval Training, which is a form of cardiovascular exercise that involves doing several repetitions of high intensity with periods of low intensity in between, for example sprinting for 15 seconds and then walking for 60 seconds, and repeating several times.
There are multiple ways of doing HIIT, for example running, cycling and jumping rope.
This form of training has several advantages over regular low intensity exercise, research has shown that HIIT can increase natural hgh production (human growth hormone) and fat burning for up to 24 hours after a workout.
HIIT workouts are also typically shorter than their lower intensity counterparts and 15-20 minutes are considered sufficient to get a good workout.
For these kind of workouts to be effective, you need to exceed the lactate threshold because lactate in the muscles acts as a stimulus to increase growth hormone production.
This happens when your muscles need to release a lot of energy in a very short time, and the cardiovascular system can’t keep up feeding the muscles oxygen.
When your muscles need to continue releasing energy, but aren’t getting enough oxygen, they start turning glucose into lactate as a form of short term energy release. This is also known as anaerobic exercise.
In a standard HIIT workout, the lactate threshold is exceeded several times, with a short time for recovery in between.
The picture on the right is of Usain Bolt, the world champion at both 100m and 200m sprint. As you can see, he is muscular and has a very low bodyfat. Take a look at this picture of Haile Gebrselassie for comparison, the Marathon world record holder.
His bodyfat is very low also but his muscles are small and he looks weak.
These two pictures don’t prove anything, but this is a common sight. Sprinters are muscular and long distance runners are not.
HIIT exercise causes a much greater increase of natural hgh than low intensity exercise and according to one study, low intensity training did not raise growth hormone above baseline at all (1).
Patients with McArdles disease are unable to produce lactate, and a study shows that these patients do not have increased levels of growth hormone after exercise, suggesting that lactate is the main stimulus for its production (2).
Growth hormone has multiple positive effects on the body, including enhanced fat burning.
HIIT enhances Excess Post-Exercise Oxygen Consumption (EPOC) more than low intensity exercise (3), suggesting that metabolism is elevated for a while after training.
Another study suggests that after high intensity weight lifting, this effect can last for up to 38 hours (4).
Research comparing two groups, one doing high intensity intervals and the other doing endurance training, showed that the HIIT lost three times the subcutaneous fat as the endurance training group, measured by body fat calipers, despite using less energy during the actual workout (5).
This suggests that HIIT is much more effective for fat loss than low intensity training.
There are many research studies displaying the superiority of high intensity exercise with regards to fat burning, in addition to positive effects on health and physique.
These kind of exercises can also be done in a much shorter time period than with low intensity cardio. People who have health issues may want to take this slowly or talk to their doctor before incorporating this into their exercise program.
It is not a good idea to do this many times per week, once or twice being an absolute maximum. This form of exercise is very taxing on the body and may lead to exhaustion if proper rest is not taken between workouts. It’s not recommended to do HIIT at the same day you do another kind of workout.
Some sports, such as crossfit, soccer and gymnastics, automatically include some form of HIIT training into their programs and should therefore automatically increase natural hgh production.