If you are into getting in shape, then you have probably heard the term High Intensity Interval Training (HIIT). High Intensity Interval Training (HIIT) is a type of intense fitness training approach in which low to moderate intensity intervals are alternated with high intensity intervals.

While High Intensity Interval Training (HIIT) has become a popular way to burn fat quickly, High Intensity Interval Training (HIIT) is also being usede in gyms and training centers across the country to increase endurance and improve athletic performance in sports where intensity varies constantly (boxing, MMA athletes, soccer players, basketball players, wrestlers’, etc.) and where athletes need the ability to repeat short maximal efforts, with low-intensity recovery periods

High Intensity Interval Training (HIIT) can be applied to several types of fitness training, such as cardio (bike, stair stepper, treadmill, etc.) and weightlifting. When applied top weightlifting, it can also be focused on individual weight training exercises such as squatting.

High Intensity Interval Training Research

Research shows that High Intensity Interval Training (HIIT) can burn adipose (fat) tissue more than up to 50% more effectively than low-intensity exercise and moderate intensity exercise.^{(1, 2,3,4,5)} Bryner et al found a significant loss in body fat in a group that exercised at a high intensity of 80-90% of maximum heart rate, while no significant change in body fat was found in the lower intensity group which exercised at 60-70% of maximum heart rate; no significant difference in total work existed between groups.⁽²⁾ Pacheco-Sanchez et al found a more pronounced fat loss in rats that exercised at a high intensity as compared to rats that exercised at a low intensity, despite both groups performing an equivalent amount of work.⁽³⁾  An epidemiological study by Tremblay et al found that individuals who regularly engaged in high-intensity exercise had lower skinfold thicknesses and waist-to-hip ratios (WHRs) than individuals who participated in exercise of lower intensities.⁽⁵⁾ 

High Intensity Interval Training (HIIT) has also been shown to speed up your metabolism which helps you burn more calories throughout the day.⁽⁶⁾ 

Several High Intensity Interval Training (HIIT) studies show that high-intensity cardio intervals with very short rests, is a very intense workout that maximally stresses both aerobic and anaerobic systems. Intervals with longer rest periods, does not stress both the anaerobic and aerobic energy systems as much, and so more work can be done until fatigue. Longer rests between the High Intensity Interval Training (HIIT) intervals are more effective for anaerobic recovery training, as the body can learn to buffer the acidosis and mobilize the anaerobic enzymes during the rest period.  

High Intensity Interval Training (HIIT) Increases Fat Loss

Without question, High Intensity Interval Training (HIIT) is one of the most effective means available for rapidly losing body fat and improving your cardiovascular conditioning. Not only do you burn many more calories while you're performing High Intensity Interval Training (HIIT), you also stimulate your metabolism to a far greater degree than low to moderate intensity training, which most people still believe is best for fat loss.^{(1, 2,3,4, 5,6)} 

High Intensity Interval Training (HIIT) Raises Metabolic Rate

High Intensity Interval Training (HIIT) burns a larger number of total calories than low-intensity exercise, and more calories burned results in greater fat loss. While engaging in High Intensity Interval Training (HIIT), the majority of calories burned will come once you have stopped finished workout. High Intensity Interval Training (HIIT) works because High Intensity Interval Training (HIIT) increases the body's metaboloc rate.⁽⁶⁾  

High Intensity Interval Training (HIIT) Builds Endurance

High Intensity Interval Training (HIIT) is considered to be much more effective than normal cardio because the intensity is higher and you are able to increase both your aerobic and anaerobic (without oxygen) endurance while burning more fat than before. Improving both aerobic and anaerobic endurance is very important for fitness. Most people understand the need to improve aerobic conditioning, but many people are unaware that the anaerobic energy system is what provides energy for all maximal effort up to 1 minute. Therefore to improve overall conditioning it is also important to improve anaerobic endurance.

People who can Benefit from High Intensity Interval Training (HIIT)

There are several people who can benefit from High Intensity Interval Training (HIIT)

• People looking to burn as much fat as possible during a cutting phase
• People looking to minimize fat gain during a bulking phase 
• People looking to burn more calories
• People looking to increase their basal metabolic rate (BMR)
• People looking to increase aerobic endurance
• People looking to increase anaerobic endurance
• Athletes who participate in a sport where the intensity varies constantly (boxing, MMA athletes, soccer players, basketball players, wrestlers’, etc.) and who need the ability to repeat short maximal efforts, with low-intensity recovery periods
• People looking to break performance plateaus, including those within the gym, will also benefit

Interval training is based on a very simple concept: go fast then go slow. Repeat. It sounds easy, but within this simple formula lies a tremendous number of possible variations and strategies you can employ to take full advantage of the power available to you.  

High Intensity Interval Training (HIIT) can be used with a few different goals in mind. High Intensity Interval Training (HIIT) programs can be designed to focus on fat loss, on strength building, on improving aerobic and anaerobic endurance or even a combination of each. Of course, if the focus it to use High Intensity Interval Training to lose fat, then it must be used along with a diet designed to preserve muscle and lose fat as well.

High Intensity Interval Training (HIIT)  can be performed on almost any cardiovascular machine (including the treadmill, stair machine, stationary bike, elliptical trainer, etc.) as well as almost any type of cardiovascular exercise (such as cycling, running, swimming, etc.).

General High Intensity Interval Training (HIIT) Guidelines

• Get medically cleared. High Intensity Interval Training (HIIT) is not for beginner exercisers or people with cardiovascular problems or risk factors. Before starting any High Intensity Interval Training (HIIT) program, you should have clearance from your medical physician. 
• Start gradually. Because High Intensity Interval Training (HIIT) is physically demanding, it’s essential to gradually build up your training program so that you don’t overtrain or hurt yourself. Before starting any High Intensity Interval Training (HIIT) program, you should be able to exercise for at least 20-30 minutes at 70-85% of your estimated maximum heart rate, without exhausting yourself or having problems.
• Warm up and cool down. Always warm up and cool down for at least five minutes before and after each High Intensity Interval Training (HIIT) session. This will reduce your risk for injuries.
• Feel the burn. Work as hard as you can during the high intensity intervals of the High Intensity Interval Training (HIIT) routine, until you feel the burning sensation in your muscles. The burn is from lactic acid and indicates that you have entered the anaerobic zone. This phase of the High Intensity Interval Training (HIIT) routine is an important phase for building endurance and burning fat.
• Keep the high intensity portion limited to 1 to 3 minutes. It is important to recognize that tests show that elite athletes can only sustain maximum intensity exercise for three to five minutes before they have to slow down and recover, so don’t expect to work longer than that. If you try you are sure to overtrain and diminish optimal results.
• Timing IS everything. Full recovery takes about four minutes for everyone, but you can shorten the recovery intervals if your high intensity intervals are also shorter and don’t completely exhaust your anaerobic energy system. If your heart rate does not drop back down to about 70% of your max during recovery intervals of the  you may need to shorten your work intervals and/or lengthen your recovery intervals.
• Stop if you feel pain. If you experience any chest pain or breathing difficulties during your High Intensity Interval Training (HIIT) workout, cool down immediately. Don't just stop or else blood can pool in your extremities and lightheadedness or faintness can occur.)

Specific High Intensity Interval Training (HIIT) Routines

For specific examples of how to use High Intensity Interval Training (HIIT) to burn fat, and to increase edurance quickly, click here.

High Intensity Interval Training (HIIT) Drawbacks

Like with any workout approach there are positives and negatives involved. The following are potential drawbacks of High Intensity Interval Training (HIIT) training.

Potential Overtraining from High Intensity Interval Training (HIIT)

High Intensity Interval Training (HIIT) is intense, hence the name ‘High Intensity Interval Training’ (HIIT). Because High Intensity Interval Training (HIIT) is an advanced technique, it is possible that using the technique too often and without adequate rest and recovery time could result in overtraining.

Increase Risk of Injury from High Intensity Interval Training (HIIT)

High Intensity Interval Training (HIIT) can increase the risk of injury for several reasons. High Intensity Interval Training (HIIT) leads to a higher risk of becoming injured to those that are injury prone and/or over weight. Because the workout pace is very intense, one wrong movement and you could seriously harm your muscles, tendons, or bones.

Sacrifice in Strength Development from High Intensity Interval Training (HIIT)

When using High Intensity Interval Training (HIIT) for weight training, since it is so intense, muscle failure will typically occur much sooner. While High Intensity Interval Training (HIIT) builds endurance and stimulates different muscle fibers and muscle hypertrophy, High Intensity Interval Training (HIIT) does result in a sacrifice in strength. Additionally, ifHigh Intensity Interval Training (HIIT) is used too often and your body does not get adequate rest to fully repair, you will tire out and your future strength training sessions will also suffer.

Bottom Line on High Intensity Interval Training (HIIT)

There is definitely enough evidence today that High Intensity Interval Training (HIIT) is superior to Steady State exercise for fat loss and for endurance. Therefore incorporating High Intensity Interval Training (HIIT) can be a very effective training approach if your goals include burning fat, burning maximum calories, and increasing conditioning and endurance. Because High Intensity Interval Training (HIIT) can be applied to several types of fitness training, including cardio (bike, stair stepper, treadmill, etc.) and weightlifting and can be adjusted to all fitness levels incorporating, there is no good reason not incorporate High Intensity Interval Training (HIIT) to your wokouts if you goal is fitness success.

References

1. Bryner, R.W., R.C. Toffle, I.H. Ullrish, and R.A. Yeater. The effects of exercise intensity on body composition, weight loss, and dietary composition in women. J. Am. Col. Nutr. 16:68-73, 1997.
2. Chesley A, Hultman E, Spriet LL. Effects of epinephrine infusion on muscle glycogenolysis during intense aerobic exercise. Am J Physiol 1995;268:E127-34.
3. Pacheco-Sanchez, M., and K.K Grunewald. Body fat deposition: effects of dietary fat and two exercise protocols. J. Am. Col. Nutr. 13:601-607, 1994.
4. Tremblay, A., J. Simoneau, and C. Bouchard. Impact of Exercise Intensity on Body Fatness and Skeletal Muscle Metabolism. Metabolism. 43(7):814-818. 1994.
5. Tremblay, A., J. DesprÃs, C. Leblanc, C.L. Craig, B. Ferris, T. Stephens, and C. Bouchard. Effect of intensity of physical activity on body fatness and fat distribution. Am J. Clin. Nutr. 51:153-157, 1990.
6. Bahr, R., and O.M. Sejersted. Effect of intensity of exercise on excess postexercise O2 consumption. Metabolism. 40:836-841, 1991.

About the Author Jeff Behar

Jeff Behar, MS, MBA