Hiit (High Intensity Interval Training)

High-intensity interval training (HIIT) or sprint interval training is an exercise strategy that is intended to improve performance with short training sessions. HIIT is a form of cardiovascular exercise which is beneficial to burning fat in a short and intense workout. Usual HIIT sessions may vary from 9–20 minutes. The original protocol set a 2:1 ratio for work to recovery periods. For example, a runner would alternate 15–20 seconds of hard sprinting with 10 seconds of jogging or walking.

A HIIT session consists of a warm up period of exercise, followed by six to ten repetitions of high intensity exercise, separated by medium intensity exercise, 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. The goal is to do at least six cycles, and to have the entire HIIT session last at least fifteen minutes and not more than twenty.
HIIT is considered to be an excellent way to maximize a workout that is limited on time.

Studies have explored the effectiveness of this method compared to traditional endurance training methods. One such study demonstrated 2.5 hours of sprint interval training produced similar biochemical muscle changes to 10.5 hours of endurance training and similar endurance performance benefits. According to another study HIIT increases the resting metabolic rate (RMR) for the following 24 hours due to excess post-exercise oxygen consumption, and may improve maximal oxygen consumption more effectively than doing only traditional, long aerobic workouts.

Long aerobic workouts have been promoted as the best method to reduce fat, as fatty acid utilization usually occurs after at least 30 minutes of training. HIIT is somewhat counterintuitive in this regard, but has nonetheless been shown to burn fat more effectively. There may be a number of factors that contribute to this, including an increase in RMR, and possibly other physiological effects.

An effective method for burning fat when you are doing cardiovascular exercise is to use interval training workouts. This workout incorporates short high-intensity bursts with lower overall effort which keeps the body burning calories long after working out.[citation needed] Interval training is also beneficial for people who play sports because of the "start-and-stop motions with periods of sprinting or close-to-sprinting speeds followed by light jogging or rest."

High-intensity interval training has also been shown to improve athletic performance. For already well-trained athletes, improvements in performance become difficult to attain and increases in training volume can potentially yield no improvements. Previous research would suggest that, for athletes who are already trained, improvements in endurance performance can be achieved through high-intensity interval training.
Ina recent study it has been shown that two weeks of HIIT can substantially improve insulin action in young healthy men. HIIT may therefore represent a viable method for prevention of type-2 diabetes.