High-intensity interval training (HIIT), also called high-intensity intermittent exercise (HIIE) or sprint interval training (SIT), is an enhanced form of interval training, an exercise strategy alternating periods of short intense anaerobic exercise with less-intense recovery periods.
HIIT is a form of cardiovascular exercise. Usual HIIT sessions may vary from 4–30 minutes. These short, intense workouts provide improved athletic capacity and condition, improved glucose metabolism, and improved fat burning
The HIIE induces a number of significant changes including:
- weight loss (average loss 1.5 kg)
- fat loss (average loss 2.0 kg)
- a reduction in ‘visceral’ fat (fat found in and around the organs that is particularly strongly linked with chronic diseases such as heart disease and type 2 diabetes)
- a reduction in waist circumference
- an increase in fat-free mass (mainly muscle)
- increased fitness
- increased power output
- reduced carbohydrate metabolism
- increased fat metabolism (average increase of 13 per cent)
A HIIT session often consists of a warm up period of exercise, followed by three to ten repetitions of high intensity exercise, separated by medium intensity exercise for recovery, and ending with a period of cool down exercise. The high intensity exercise should be done at near maximum intensity. The medium exercise should be about 50% intensity. The number of repetitions and length of each depends on the exercise, but may be as little as three repetitions with just 20 seconds of intense exercise.
There is no specific formula to HIIT. Depending on one’s level of cardiovascular development, the moderate-level intensity can be as slow as walking.