HIIT involves short bursts of intense exercise alternated with low-intensity recovery periods. Interestingly, it is perhaps the most time-efficient way to exercise

Typically, a HIIT workout will range from 7 to 30 minutes in duration.

Despite how short the workout is, it can produce health benefits similar to twice as much moderate-intensity exercise

The actual activity being performed varies but can include sprinting, biking, jump rope or other body weight exercises.

For example, a HIIT workout using a stationary exercise bike could consist of 30 seconds of cycling as fast as possible against high resistance, followed by several minutes of slow, easy cycling with low resistance.

Regardless of how it is implemented, high-intensity intervals should involve short periods of vigorous exercise that make your heart rate speed up

Not only does HIIT provide the benefits of longer-duration exercise in a much shorter amount of time — it may also provide some unique health benefits

You can burn calories quickly using HIIT (9Trusted Source, 10Trusted Source).

One study compared the calories burned during 30 minutes each of HIIT, weight training, running and biking.

The researchers found that HIIT burned 25–30% more calories than the other forms of exercise (9Trusted Source).

In this study, a HIIT repetition consisted of 20 seconds of maximal effort, followed by 40 seconds of rest.

This means that the participants were actually only exercising for 1/3 of the time that the running and biking groups were.

Although each workout session was 30 minutes long in this study, it is common for HIIT workouts to be much shorter than traditional exercise sessions.

This is because HIIT allows you to burn about the same amount of calories, but spend less time exercising.

Summary: HIIT may help you burn more calories than traditional exercise, or burn the same amount of calories in a shorter amount of time.

One of the ways HIIT helps you burn calories actually comes after you are done exercising.

Several studies have demonstrated HIIT's impressive ability to increase your metabolic rate for hours after exercise (11Trusted Source, 12Trusted Source, 13Trusted Source).

Some researchers have even found that HIIT increases your metabolism after exercise more so than jogging and weight training (11Trusted Source).

In the same study, HIIT was also found to shift the body's metabolism toward using fat for energy rather than carbs.

Another study showed that just two minutes of HIIT in the form of sprints increased metabolism over 24 hours as much as 30 minutes of running (14Trusted Source).

Summary: Due to the intensity of the workout, HIIT can elevate your metabolism for hours after exercise. This results in additional calories being burned even after you have finished exercising.

Studies have shown that HIIT can help you lose fat.

One review looked at 13 experiments and 424 overweight and obese adults.

Interestingly, it found that both HIIT and traditional moderate-intensity exercise can reduce body fat and waist circumference (15Trusted Source).

Additionally, one study found that people performing HIIT three times per week for 20 minutes per session lost 4.4 pounds, or 2 kgs, of body fat in 12 weeks — without any dietary changes (16Trusted Source).

Perhaps more important was the 17% reduction in visceral fat, or the disease-promoting fat surrounding your internal organs.

Several other studies also indicate that body fat can be reduced with HIIT, despite the relatively low time commitment (17Trusted Source, 18Trusted Source, 19Trusted Source).

However, like other forms of exercise, HIIT may be most effective for fat loss in those who are overweight or obese (20, 21Trusted Source).

Summary: High-intensity intervals can produce similar fat loss to traditional endurance exercise, even with a much smaller time commitment. They can also reduce unhealthy visceral fat.

In addition to helping with fat loss, HIIT could help increase muscle mass in certain individuals (21Trusted Source, 22Trusted Source, 23Trusted Source).

However, the gain in muscle mass is primarily in the muscles being used the most, often the trunk and legs (16Trusted Source, 21Trusted Source, 23Trusted Source).

Additionally, it's important to note that increases in muscle mass are more likely to occur in individuals who were less active to begin with (24Trusted Source).

Some research in active individuals has failed to show higher muscle mass after HIIT programs (25Trusted Source).

Weight training continues to be the "gold standard" form of exercise to increase muscle mass, but high-intensity intervals could support a small amount of muscle growth (24Trusted Source, 26Trusted Source).

Summary: If you are not very active, you may gain some muscle by starting HIIT but not as much as if you performed weight training.

Oxygen consumption refers to your muscles' ability to use oxygen, and endurance training is typically used to improve your oxygen consumption.

Traditionally, this consists of long sessions of continuous running or cycling at a steady rate.

However, it appears that HIIT can produce the same benefits in a shorter amount of time (20, 21Trusted Source, 27Trusted Source).

One study found that five weeks of HIIT workouts performed four days per week for 20 minutes each session improved oxygen consumption by 9% (6Trusted Source).

This was almost identical to the improvement in oxygen consumption in the other group in the study, who cycled continuously for 40 minutes per day, four days per week.

Another study found that eight weeks of exercising on the stationary bike using traditional exercise or HIIT increased oxygen consumption by about 25% (7Trusted Source).

Once again, the total time exercising was much different between groups: 120 minutes per week for the traditional exercise versus only 60 minutes per week of HIIT.

Additional studies also demonstrate that HIIT can improve oxygen consumption (25Trusted Source, 28Trusted Source).

Summary: High-intensity interval training can improve oxygen consumption as much as traditional endurance training, even if you only exercise about half as long.

HIIT may have important health benefits, as well.

A large amount of research indicates that it can reduce heart rate and blood pressure in overweight and obese individuals, who often have high blood pressure (20).

One study found that eight weeks of HIIT on a stationary bike decreased blood pressure as much as traditional continuous endurance training in adults with high blood pressure (7Trusted Source).

In this study, the endurance training group exercised four days per week for 30 minutes per day, but the HIIT group only exercised three times per week for 20 minutes per day.

Some researchers have found that HIIT may even reduce blood pressure more than the frequently recommended moderate-intensity exercise (29Trusted Source).

However, it appears that high-intensity exercise does not typically change blood pressure in normal-weight individuals with normal blood pressure (20).

Summary: HIIT can reduce blood pressure and heart rate, primarily in overweight or obese individuals with high blood pressure.