HIIT: The optimal protocol for fat loss?

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    HIIT: The optimal protocol for fat loss?


    It being close to cutting season and all I thought I'd start it of with an article about my favorite cardio style: HIIT

    <B>HIGH-INTENSITY&nbsp; INTERVAL TRAINING:
    THE&nbsp; OPTIMAL PROTOCOL FOR FAT LOSS?</B>
    James Krieger

    As exercise intensity increases, the proportion of fat&nbsp; utilized as an energy substrate decreases, while the&nbsp; proportion of carbohydrates utilized increases (5). The&nbsp; rate of fatty acid mobilization from adipose tissue also&nbsp; declines with increasing exercise intensity (5). This had&nbsp; led to the common recommendation that low- to moderate-intensity,&nbsp; long duration endurance exercise is the most beneficial&nbsp; for fat loss (15). However, this belief does not take&nbsp; into consideration what happens during the post-exercise&nbsp; recovery period; total daily energy expenditure is more&nbsp; important for fat loss than the predominant fuel utilized&nbsp; during exercise (5). This is supported by research&nbsp; showing no significant difference in body fat loss&nbsp; between high-intensity and low-intensity submaximal,&nbsp; continuous exercise when total energy expenditure per&nbsp; exercise session is equated (2,7,9). Research by Hickson&nbsp; et al (11) further supports the notion that the&nbsp; predominant fuel substrate used during exercise does not&nbsp; play a role in fat loss; rats engaged in a high-intensity&nbsp; sprint training protocol achieved significant reductions&nbsp; in body fat, despite the fact that sprint training relies&nbsp; almost completely on carbohydrates as a fuel source. Some research suggests that high-intensity exercise is&nbsp; more beneficial for fat loss than low- and moderate-intensity&nbsp; exercise (3,18,23,24). Pacheco-Sanchez et al (18) found a&nbsp; more pronounced fat loss in rats that exercised at a high&nbsp; intensity as compared to rats that exercised at a low&nbsp; intensity, despite both groups performing an equivalent&nbsp; amount of work. Bryner et al (3) found a significant loss&nbsp; in body fat in a group that exercised at a high intensity&nbsp; of 80-90% of maximum heart rate, while no significant&nbsp; change in body fat was found in the lower intensity group&nbsp; which exercised at 60-70% of maximum heart rate; no&nbsp; significant difference in total work existed between&nbsp; groups. An epidemiological study (24) found that&nbsp; individuals who regularly engaged in high-intensity&nbsp; exercise had lower skinfold thicknesses and waist-to-hip&nbsp; ratios (WHRs) than individuals who participated in&nbsp; exercise of lower intensities. After a covariance&nbsp; analysis was performed to remove the effect of total&nbsp; energy expenditure on skinfolds and WHRs, a significant&nbsp; difference remained between people who performed high-intensity&nbsp; exercise and people who performed lower-intensity&nbsp; exercise. Tremblay et al (23) performed the most notable study&nbsp; which demonstrates that high-intensity exercise,&nbsp; specifically intermittent, supramaximal exercise, is the&nbsp; most optimal for fat loss. Subjects engaged in either an&nbsp; endurance training (ET) program for 20 weeks or a high-intensity&nbsp; intermittent-training (HIIT) program for 15 weeks. The&nbsp; mean estimated energy cost of the ET protocol was 120.4&nbsp; MJ, while the mean estimated energy cost of the HIIT&nbsp; protocol was 57.9 MJ. The decrease in six subcutaneous&nbsp; skinfolds tended to be greater in the HIIT group than the&nbsp; ET group, despite the dramatically lower energy cost of&nbsp; training. When expressed on a per MJ basis, the HIIT&nbsp; group's reduction in skinfolds was nine times greater&nbsp; than the ET group. A number of explanations exist for the greater amounts&nbsp; of fat loss achieved by HIIT. First, a large body of&nbsp; evidence shows that high-intensity protocols, notably&nbsp; intermittent protocols, result in significantly greater&nbsp; post-exercise energy expenditure and fat utilization than&nbsp; low- or moderate-intensity protocols (1,4,8,14,19,21,25).&nbsp; Other research has found significantly elevated blood&nbsp; free-fatty-acid (FFA) concentrations or increased&nbsp; utilization of fat during recovery from resistance&nbsp; training (which is a form of HIIT) (16,17). Rasmussen et&nbsp; al (20) found higher exercise intensity resulted in&nbsp; greater acetyl-CoA carboxylase (ACC) inactivation, which&nbsp; would result in greater FFA oxidation after exercise&nbsp; since ACC is an inhibitor of FFA oxidation. Tremblay et&nbsp; al (23) found HIIT to significantly increase muscle 3-hydroxyacyl&nbsp; coenzyme A dehydrogenase activity (a marker of the&nbsp; activity of b oxidation) over&nbsp; ET. Finally, a number of studies have found high-intensity&nbsp; exercise to suppress appetite more than lower intensities&nbsp; (6,12,13,22) and reduce saturated fat intake (3). Overall, the evidence suggests that HIIT is the most&nbsp; efficient method for achieving fat loss. However, HIIT&nbsp; carries a greater risk of injury and is physically and&nbsp; psychologically demanding (10), making low- and moderate-intensity,&nbsp; continuous exercise the best choice for individuals that&nbsp; are unmotivated or contraindicated for high-intensity&nbsp; exercise.

    1. <B>Bahr, R., and O.M. Sejersted.</B> Effect of&nbsp; intensity of exercise on excess postexercise O<SUB>2 </SUB>consumption. <I>Metabolism.</I> 40:836-841, 1991.

    2. <B>Ballor, D.L., J.P. McCarthy, and E.J. Wilterdink.</B> Exercise intensity does not affect the composition of&nbsp; diet- and exercise-induced body mass loss. <I>Am. J. Clin.&nbsp; Nutr.</I> 51:142-146, 1990.

    3. <B>Bryner, R.W., R.C. Toffle, I.H. Ullrish, and R.A.&nbsp; Yeater.</B> The effects of exercise intensity on body&nbsp; composition, weight loss, and dietary composition in&nbsp; women. <I>J. Am. Col. Nutr.</I> 16:68-73, 1997.&nbsp;

    4. <B>Burleson, Jr, M.A., H.S. O'Bryant, M.H. Stone, M.A.&nbsp; Collins, and T. Triplett-McBride.</B> Effect of weight&nbsp; training exercise and treadmill exercise on post-exercise&nbsp; oxygen consumption. <I>Med. Sci. Sports Exerc. </I>30:518-522,&nbsp; 1998.&nbsp; 5. <B>Coyle, E.H.</B> Fat Metabolism During Exercise.&nbsp; [Online] Gatorade Sports Science Institute. http://www.gssiweb.com/references/s0...06d.html&nbsp; [1999, Mar 25]

    6. <B>Dickson-Parnell, B.E., and A. Zeichner.</B> Effects of a short-term exercise program on caloric&nbsp; consumption. <I>Health Psychol.</I> 4:437-448, 1985.

    7. <B>Gaesser, G.A., and R.G. Rich.</B> Effects of&nbsp; high- and low-intensity exercise training on aerobic&nbsp; capacity and blood lipids. <I>Med. Sci. Sports Exerc.</I> 16:269-274, 1984.

    8. <B>Gillette, C.A., R.C. Bullough, and C.L. Melby.</B> Postexercise energy expenditure in response to acute&nbsp; aerobic or resistive exercise. <I>Int. J. Sports Nutr.</I> 4:347-360, 1994.

    9. <B>Grediagin, M.A., M. Cody, J. Rupp, D. Benardot,&nbsp; and R. Shern.</B> Exercise intensity does not effect body&nbsp; composition change in untrained, moderately overfat women. <I>J. Am. Diet Assoc.</I> 95:661-665, 1995.&nbsp;

    10. <B>Grubbs, L.</B> The critical role of exercise in&nbsp; weight control. <I>Nurse Pract.</I> 18(4):20,22,25-26,29,&nbsp; 1993.

    11. <B>Hickson, R.C., W.W. Heusner, W.D. Van Huss, D.E.&nbsp; Jackson, D.A. Anderson, D.A. Jones, and A.T. Psaledas.</B> Effects of Dianabol and high-intensity sprint training on&nbsp; body composition of rats. <I>Med. Sci. Sports.</I> 8:191-195,&nbsp; 1976.

    12. <B>Imbeault, P., S. Saint-Pierre, N. Alméras, and&nbsp; A. Tremblay.</B> Acute effects of exercise on energy&nbsp; intake and feeding behaviour. <I>Br. J. Nutr.</I> 77:511-521,&nbsp; 1997.

    13. <B>Katch, F.I., R. Martin, and J. Martin.</B> Effects of exercise intensity on food consumption in the&nbsp; male rat. <I>Am J. Clin. Nutr.</I> 32:1401-1407, 1979.

    14. <B>Laforgia, J. R.T. Withers, N.J. Shipp, and C.J.&nbsp; Gore. </B>Comparison of energy expenditure elevations&nbsp; after submaximal and supramaximal running. <I>J. Appl.&nbsp; Physiol.</I> 82:661-666, 1997.

    15. <B>Mahler, D.A., V.F. Froelicher, N.H. Miller, and&nbsp; T.D. York.</B><I> ACSM's Guidelines for Exercise Testing&nbsp; and Prescription</I>, edited by W.L. Kenney, R.H.&nbsp; Humphrey, and C.X. Bryant. Media, PA: Williams and&nbsp; Wilkins, 1995, chapt. 10, p. 218-219.

    16. <B>McMillan, J.L., M.H. Stone, J. Sartin, R. Keith,&nbsp; D. Marple, Lt. C. Brown, and R.D. Lewis.</B> 20-hour&nbsp; physiological responses to a single weight-training&nbsp; session<I>. J. Strength Cond. Res.</I> 7(3):9-21, 1993.

    17. <B>Melby, C., C. Scholl, G. Edwards, and R.&nbsp; Bullough.</B> Effect of acute resistance exercise on&nbsp; postexercise energy expenditure and resting metabolic&nbsp; rate. <I>J. Appl. Physiol.</I> 75:1847-1853, 1993.

    18. <B>Pacheco-Sanchez, M., and K.K Grunewald.</B> Body fat deposition: effects of dietary fat and two&nbsp; exercise protocols. <I>J. Am. Col. Nutr. </I>13:601-607,&nbsp; 1994.

    19. <B>Phelain, J.F., E. Reinke, M.A. Harris, and C.L.&nbsp; Melby.</B> Postexercise energy expenditure and substrate&nbsp; oxidation in young women resulting from exercise bouts of&nbsp; different intensity<I>. J. Am. Col. Nutr.</I> 16:140-146,&nbsp; 1997.

    20. <B>Rasmussen, B.B., and W.W. Winder.</B> Effect of&nbsp; exercise intensity on skeletal muscle malonyl-CoA and&nbsp; acetyl-CoA carboxylase. <I>J. Appl. Physiol.</I> 83:1104-1109,&nbsp; 1997.

    21. <B>Smith, J., and L. McNaughton.</B> The effects&nbsp; of intensity of exercise on excess postexercise oxygen&nbsp; consumption and energy expenditure in moderately trained&nbsp; men and women. <I>Eur. J. Appl. Physiol.</I> 67:420-425,&nbsp; 1993.

    22. <B>Thompson, D.A., L.A. Wolfe, and R. Eikelboom.</B> Acute effects of exercise intensity on appetite in young&nbsp; men. <I>Med. Sci. Sports Exerc.</I> 20:222-227, 1988.

    23. <B>Tremblay, A., J. Simoneau, and C. Bouchard.</B> Impact of exercise intensity on body fatness and skeletal&nbsp; muscle metabolism. <I>Metabolism.</I> 43:814-818, 1994.

    24. <B>Tremblay, A., J. Després, C. Leblanc, C.L.&nbsp; Craig, B. Ferris, T. Stephens, and C. Bouchard.</B> Effect of intensity of physical activity on body fatness&nbsp; and fat distribution. <I>Am J. Clin. Nutr.</I> 51:153-157,&nbsp; 1990.

    25. <B>Treuth, M.S., G.R. Hunter, and M. Williams.</B> Effects of exercise intensity on 24-h energy expenditure&nbsp; and substrate oxidation. <I>Med. Sci. Sports Exerc.</I> 28:1138-1143, 1996.


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    Sheesh's Avatar
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    Nice post LG

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    Interesting reading. Thanks for sharing, LG.

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    excellent, scientific vindication for those who hypothesised about this before research was available and their disciples (LG and myself among others). if you are doing cardio at low intensity (ie walking on a treadmill - hey wait a minute, that doesn't count) you are probably wasting your time.

    go hard or go home, cheers, pete

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