Just about everyone and his mama has heard about High Intensity Interval Training, or H.I.I.T. for short. H.I.I.T. has been found to have various advantages over other forms of exercise for both fat loss and retaining muscle mass. It seems everyone has jumped on the H.I.I.T. bandwagon and regularly talk about how they do 40 minutes or so of H.I.I.T. and so on. The problem is, most of the people who claim to be doing H.I.I.T. are not. A quick hint: if the person was doing true H.I.I.T., they would not be able to do 20 minutes of it, much less 40!

Many, if not most, people seem to confuse H.I.I.T. with regular interval training. H.I.I.T. is in fact a form of interval training, but not all interval training is H.I.I.T.. Put simply, Interval training is a varying of intensities within the same workout, where you alternate a low intensity bout with a higher intensity bout. That’s the general nature of interval training, but it aint H.I.I.T. training folks. H.I.I.T. training, is a low intensity/no intensity bout alternated with a maximal intensity bout. By maximal, I mean 100% effort, which of course, no one can achieve for more then 20-30 seconds at a time.

There are various ways to perform H.I.I.T., but all have that in common, and what most people think they are doing for H.I.I.T. is really just old fashioned interval training. For example, the other day I did 4 minutes of walking on a treadmill at 3.5mph hour followed by 1 minute of running at 8.5mph (which for my short legs is pretty fast pace!) and repeated the cycle 5 times, which meant I was doing a 1:4 run/walk that lasted about 30 minutes including warm up and warm down. Was that H.I.I.T.? No, it was not. It was interval training, which is effective and productive training, but it’s not H.I.I.T..

ManTReadmillRunThere are many ways to perform H.I.I.T. training, from Tabata protocols (the most intense form of H.I.I.T.) which may only last 4-5 minutes to other versions. For example, my current H.I.I.T. protocol goes like so: after a brief warm up – 5 minutes or so on the treadmill – I will use a stair stepper type machine and will do 1 minute low intensity followed by 30 seconds all out, and repeat. I will do that for 10 minutes, which is literally all I can stand. When I say “all out” I mean 100% intensity, nothing held back, as fast and as hard as my legs can move me, similar say to a full sprint on a track.

I like the stair stepper because it’s non-impactive on the joints and it’s easy to speed up and slow down quickly, but there are many ways to do H.I.I.T. training. The fact is however, most people claiming to do H.I.I.T. are not. H.I.I.T. is not for everyone. It requires a higher level of fitness, and many people are better off starting with various interval programs similar to what I wrote above vs. H.I.I.T.. Done too often, and or combined with other forms of high intensity exercise (e.g., weight lifting, etc.) H.I.I.T. can and will lead to over training and or injury, or as James Krieger concludes in his excellent review on the topic below:

“H.I.I.T. carries a greater risk of injury and is physically and psychologically demanding, making low- and moderate-intensity, continuous exercise the best choice for individuals that are unmotivated or contraindicated for high-intensity exercise.”

Don’t gloss over that part.

Personally, I do H.I.I.T. training no more then once per week when combining it with weight training and will usually do the interval training outlined above, or something like it, and keep the H.I.I.T. to once per week, and as part of the Hybrid Training program I developed, is very taxing and intense. I will also take time off from the H.I.I.T. for a time, and then add it back in for a few months at a time. What follows is a nice review of the science of H.I.I.T. worth reading, but keep in mind the realities of H.I.I.T. training.

High-Intensity Interval Training: The Optimal Protocol for Fat Loss?
By James Krieger

As exercise intensity increases, the proportion of fat utilized as an energy substrate decreases, while the proportion of carbohydrates utilized increases (5). The rate of fatty acid mobilization from adipose tissue also declines with increasing exercise intensity (5). This had led to the common recommendation that low- to moderate-intensity, long duration endurance exercise is the most beneficial for fat loss (15). However, this belief does not take into consideration what happens during the post-exercise recovery period; total daily energy expenditure is more important for fat loss than the predominant fuel utilized during exercise (5). This is supported by research showing no significant difference in body fat loss between high-intensity and low-intensity submaximal, continuous exercise when total energy expenditure per exercise session is equated (2,7,9). Research by Hickson et al (11) further supports the notion that the predominant fuel substrate used during exercise does not play a role in fat loss; rats engaged in a high-intensity sprint training protocol achieved significant reductions in body fat, despite the fact that sprint training relies almost completely on carbohydrates as a fuel source.

Some research suggests that high-intensity exercise is more beneficial for fat loss than low- and moderate-intensity exercise (3,18,23,24). Pacheco-Sanchez et al (18) 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. Bryner et al (3) 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. An epidemiological study (24) 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. After a covariance analysis was performed to remove the effect of total energy expenditure on skinfolds and WHRs, a significant difference remained between people who performed high-intensity exercise and people who performed lower-intensity exercise.

Tremblay et al (23) performed the most notable study which demonstrates that high-intensity exercise, specifically intermittent, supramaximal exercise, is the most optimal for fat loss. Subjects engaged in either an endurance training (ET) program for 20 weeks or a high-intensity intermittent-training (H.I.I.T.) program for 15 weeks. The mean estimated energy cost of the ET protocol was 120.4 MJ, while the mean estimated energy cost of the H.I.I.T. protocol was 57.9 MJ. The decrease in six subcutaneous skinfolds tended to be greater in the H.I.I.T. group than the ET group, despite the dramatically lower energy cost of training. When expressed on a per MJ basis, the H.I.I.T. group’s reduction in skinfolds was nine times greater than the ET group.

A number of explanations exist for the greater amounts of fat loss achieved by H.I.I.T.. First, a large body of evidence shows that high-intensity protocols, notably intermittent protocols, result in significantly greater post-exercise energy expenditure and fat utilization than low- or moderate-intensity protocols (1,4,8,14,19,21,25). Other research has found significantly elevated blood free-fatty-acid (FFA) concentrations or increased utilization of fat during recovery from resistance training (which is a form of H.I.I.T.) (16,17).

Rasmussen et al (20) found higher exercise intensity resulted in greater acetyl-CoA carboxylase (ACC) inactivation, which would result in greater FFA oxidation after exercise since ACC is an inhibitor of FFA oxidation. Tremblay et al (23) found H.I.I.T. to significantly increase muscle 3-hydroxyacyl coenzyme A dehydrogenase activity (a marker of the activity of b oxidation) over ET. Finally, a number of studies have found high-intensity exercise to suppress appetite more than lower intensities (6,12,13,22) and reduce saturated fat intake (3).

Overall, the evidence suggests that H.I.I.T. is the most efficient method for achieving fat loss. However, H.I.I.T. carries a greater risk of injury and is physically and psychologically demanding (10), making low- and moderate-intensity, continuous exercise the best choice for individuals that are unmotivated or contraindicated for high-intensity exercise.

More on H.I.I.T.


1. Bahr, R., and O.M. Sejersted. Effect of intensity of exercise on excess postexercise O2 consumption. Metabolism. 40:836-841, 1991.
2. Ballor, D.L., J.P. McCarthy, and E.J. Wilterdink. Exercise intensity does not affect the composition of diet- and exercise-induced body mass loss. Am. J. Clin. Nutr. 51:142-146, 1990.
3. 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.
4. Burleson, Jr, M.A., H.S. O’Bryant, M.H. Stone, M.A. Collins, and T. Triplett-McBride. Effect of weight training exercise and treadmill exercise on post-exercise oxygen consumption. Med. Sci. Sports Exerc. 30:518-522, 1998.
5. Coyle, E.H. Fat Metabolism During Exercise. [Online] Gatorade Sports Science Institute. http://www.gssiweb.com/references/s0…20000006d.html [1999, Mar 25]
6. Dickson-Parnell, B.E., and A. Zeichner. Effects of a short-term exercise program on caloric consumption. Health Psychol. 4:437-448, 1985.
7. Gaesser, G.A., and R.G. Rich. Effects of high- and low-intensity exercise training on aerobic capacity and blood lipids. Med. Sci. Sports Exerc. 16:269-274, 1984.
8. Gillette, C.A., R.C. Bullough, and C.L. Melby. Postexercise energy expenditure in response to acute aerobic or resistive exercise. Int. J. Sports Nutr. 4:347-360, 1994.
9. Grediagin, M.A., M. Cody, J. Rupp, D. Benardot, and R. Shern. Exercise intensity does not effect body composition change in untrained, moderately overfat women. J. Am. Diet Assoc. 95:661-665, 1995.
10. Grubbs, L. The critical role of exercise in weight control. Nurse Pract. 18(4):20,22,25-26,29, 1993.
11. Hickson, R.C., W.W. Heusner, W.D. Van Huss, D.E. Jackson, D.A. Anderson, D.A. Jones, and A.T. Psaledas. Effects of Dianabol and high-intensity sprint training on body composition of rats. Med. Sci. Sports. 8:191-195, 1976.
12. Imbeault, P., S. Saint-Pierre, N. Alméras, and A. Tremblay. Acute effects of exercise on energy intake and feeding behaviour. Br. J. Nutr. 77:511-521, 1997.
13. Katch, F.I., R. Martin, and J. Martin. Effects of exercise intensity on food consumption in the male rat. Am J. Clin. Nutr. 32:1401-1407, 1979.
14. Laforgia, J. R.T. Withers, N.J. Shipp, and C.J. Gore. Comparison of energy expenditure elevations after submaximal and supramaximal running. J. Appl. Physiol. 82:661-666, 1997.
15. Mahler, D.A., V.F. Froelicher, N.H. Miller, and T.D. York. ACSM’s Guidelines for Exercise Testing and Prescription, edited by W.L. Kenney, R.H. Humphrey, and C.X. Bryant. Media, PA: Williams and Wilkins, 1995, chapt. 10, p. 218-219.
16. McMillan, J.L., M.H. Stone, J. Sartin, R. Keith, D. Marple, Lt. C. Brown, and R.D. Lewis. 20-hour physiological responses to a single weight-training session. J. Strength Cond. Res. 7(3):9-21, 1993.
17. Melby, C., C. Scholl, G. Edwards, and R. Bullough. Effect of acute resistance exercise on postexercise energy expenditure and resting metabolic rate. J. Appl. Physiol. 75:1847-1853, 1993.
18. 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.
19. Phelain, J.F., E. Reinke, M.A. Harris, and C.L. Melby. Postexercise energy expenditure and substrate oxidation in young women resulting from exercise bouts of different intensity. J. Am. Col. Nutr. 16:140-146, 1997.
20. Rasmussen, B.B., and W.W. Winder. Effect of exercise intensity on skeletal muscle malonyl-CoA and acetyl-CoA carboxylase. J. Appl. Physiol. 83:1104-1109, 1997.
21. Smith, J., and L. McNaughton. The effects of intensity of exercise on excess postexercise oxygen consumption and energy expenditure in moderately trained men and women. Eur. J. Appl. Physiol. 67:420-425, 1993.
22. Thompson, D.A., L.A. Wolfe, and R. Eikelboom. Acute effects of exercise intensity on appetite in young men. Med. Sci. Sports Exerc. 20:222-227, 1988.
23. Tremblay, A., J. Simoneau, and C. Bouchard. Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism. 43:814-818, 1994.
24. Tremblay, A., J. Després, 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.
25. Treuth, M.S., G.R. Hunter, and M. Williams. Effects of exercise intensity on 24-h energy expenditure and substrate oxidation. Med. Sci. Sports Exerc. 28:1138-1143, 1996.


About the Author

Brinkzone.comWill Brink, owner of BrinkZone.comis a columnist, contributing consultant, and writer for various health/fitness, medical, and bodybuilding publications. His articles relating to nutrition, supplements, weight loss, exercise and medicine can be found in such publications as Let’s Live, Muscle Media 2000, MuscleMag International, The Life Extension Magazine, Muscle & Fitness, Inside Karate, Exercise For Men Only, Body International, Power, Oxygen, Penthouse, Women’s World and The Townsend Letter For Doctors. He is the author of Priming The Anabolic Environment and Weight Loss Nutrients Revealed. He is the Consulting Sports Nutrition Editor and a monthly columnist for Physical Magazine and an Editor at Large for Power magazine. Will graduated from Harvard University with a concentration in the natural sciences, and is a consultant to major supplement, dairy, and pharmaceutical companies.

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