HIIT is not superior to moderate-intensity continuous exercise for fat loss. HIIT is not superior to moderate-intensity continuous exercise for increasing lean muscle mass.
HIIT MORE EFFECTIVE FOR FAT LOSS KEY POINTS:
- Is HIIT more effective for fat loss than traditional cardio?
- HIIT does not boost your metabolism for hours after exercise as many claim.
- Both HIIT and moderate-intensity exercise are effective for reducing body fat
Introduction
One of the most popular misconceptions is that High-Intensity Interval Training (HIIT) keeps your metabolism revved for hours after exercise. High-intensity resistance exercise burns about 8.83 kcals/minute. (1) This is slightly less than someone bicycling at a moderate effort (9.8 kcal/min) and jogging a 10-minute mile (12.3 kcal/min). (2) Metabolic rate after exercise, or what the scientific community calls EPOC (Exercise Post Oxygen Consumption), returns to baseline very quickly after exercise, usually less than an hour.
EPOC is the measure of oxygen consumption after exercise, which is a measure of metabolic rate. Many exercise factors affect EPOC, including exercise intensity and duration. The duration of EPOC is elevated after exercise is determined by ATP resynthesis, heart rate, ventilation, body temperature, hormone levels (i.e., adrenaline), lactate, glycogen replacement, etc.
HIIT STUDIES
HIIT can certainly increase metabolic rate compared to moderate and low-intensity exercise, but it’s not the massive amount that one would expect. A landmark study in 1997 compared running with either HIIT training (i.e., 20 max -1-minute intervals) to moderate-intensity exercise (i.e., 30 minutes of continuous exercise) over nine hours after exercise. The HIIT training resulted in an energy expenditure of about 57 calories greater over the nine hours.
A 2021 meta-analysis compared HIIT to moderate-intensity continuous exercise and found that HIIT post-exercise burned ~32 calories, whereas moderate-intensity exercise burned ~24 calories. (3) Thus, HIIT technically does burn more calories post-exercise, but don’t think that because you performed a HIIT gives you the green light to eat whatever you want. The calories burn post-exercise, or the afterburn effect is relatively small.
Since there are very small changes in 24-hour fat oxidation or fat burning that occurs with exercise, it’s been suggested that exercise causes a redistribution of nutrients toward muscle for fuel replenishment and cell regeneration and away from adipose tissue, causing increases in lean mass with decreases in body fat. (4)
HIIT VS. LOW-INTENSITY EXERCISE EFFECTS ON VISCERAL ADIPOSE TISSUE
High-Intensity Interval Training or HIIT can be near maximal exercise efforts with two to three-minute rest periods. Cycling classes often use sprint cycling for 30 seconds or less with two to five-minute rest periods. Although both HIIT and low-intensity exercise burn calories, there are physiological differences in adipose tissues’ response to each.
Adipose tissue can be divided into visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT). VAT is adipose tissue located around surrounding organs, whereas SAT is located under the skin. Although most people want to get rid of subcutaneous fat, VAT is more dangerous. VAT is directly related to type II diabetes, cardiovascular disease, several types of cancer, and mortality. (5, 6) Some of the more interesting aspects of how the two forms of fat affect overall health came from studies that came from liposuction surgery. Subjects who had liposuction surgery had 9.1 kg or 4.1 pounds of fat. Still, they had no health improvements such as improved insulin sensitivity or changes in glucose which occurs with regular weight loss. (7) Thus, subcutaneous fat is not causing the major health-related issues; it’s the fat surrounding the internal organs.
IS HIIT MORE EFFECTIVE FOR FAT LOSS?
Exercise training can reduce VAT and SAT without changing body weight. Exercise intensity has an important role in the reduction of VAT. VAT is much more important for overall health and wellness than SAT. In a review of the literature, high-intensity aerobic exercise without dietary restriction resulted in larger reductions in VAT than moderate and low-intensity. Moderate-intensity had a greater impact on reducing VAT than low-intensity exercise. Another interesting finding was that training duration didn’t significantly reduce VAT. (8) This indicated a certain intensity threshold for reducing VAT. Despite less fat oxidation occurring during HIIT training than in low-intensity training, HIIT training can offer several beneficial health benefits, such as reducing VAT and SAT in a shorter time and reducing body fat. (9)
REVIEW OF HIIT STUDIES
A 2020 review of the literature of 32 studies found the following when comparing HIIT modalities, duration, frequency, and intensity. (10)
a) Exercise duration greater than 150 minutes had no greater effect on reducing VAT.
b) Both aerobic exercise and HIIT were effective in decreasing VAT.
It should be mentioned that this meta-analysis included many overweight and obese subjects with metabolic diseases, such as diabetes. In a meta-analysis of healthy young adults, it was found that resistance exercise reduced body fat by 1.4% and reduced visceral fat as well. (11) VAT also has been linked to insulin resistance; it is suggested that resistance exercise reductions in VAT could be due to improved insulin sensitivity. One study found that resistance exercise resulted in a 10.3% reduction in VAT and an 11.2% reduction in SAT, and insulin sensitivity increased by 46.3%.(12)
DOES HIIT RESULT IN MORE FAT LOSS?
For several years, it has been recommended that you need to perform high-intensity interval training or HIIT to burn fat. HIIT can be defined as the exercise performed above a peak heart rate of 80% or more. HIIT is performed in multiple short bursts in which a person exercises at a hard rate and then has a brief recovery period at a slower rate. The most common example is a spin class or a treadmill program involving maximal sprints with short rest periods. Moderate-intensity continuous exercise is defined as the exercise performed less than 80% of a peak heart rate and performed over a more prolonged period of time (i.e., cycling or walking for 45 minutes). Some people advocate HIIT is superior for fat loss to other forms of exercise. HIIT is advantageous for the following reasons:
a.) it burns more calories in a short amount of time
b.) It can improve anaerobic performance and may improve lean muscle mass.
c.) HIIT can provide health benefits in a shorter period.
HIIT Alternatives
The biggest issue with HIIT is that it’s exhausting to perform, especially if you are dieting. Doing several rounds of high-intensity sprint cycling isn’t exactly realistic if you have ever been on a calorie-restricted diet for several weeks, especially if you are performing regular resistance exercise. In 2017, a literature review found that both high-intensity interval training and steady-state cardio effectively reduce body fat. (13)
A recent meta-analysis of 56 studies examined the effects of HIIT vs. moderate-intensity continuous cardio for fat loss and lean muscle mass. The results were: a.) HIIT was not superior to moderate-intensity continuous exercise for fat loss. b.) HIIT was not superior to moderate-intensity continuous exercise for increasing lean muscle mass. The review found that the exercise intensity and duration of cardio had minimal impact on the rates of fat loss. The author concluded individuals should choose the form of cardio that best suits their needs for fat loss. (14)
HIIT MORE EFFECTIVE FOR FAT LOSS KEY POINTS
- HIIT does not boost your metabolism for hours after exercise as many claim.
- There is no best exercise for fat loss
- Both HIIT and moderate-intensity exercise are effective for reducing body fat.
- Is HIIT more effective for fat loss than traditional cardio?
REFERENCES:
3. Panissa VLG, Fukuda DH, Staibano V, Marques M, Franchini E. Magnitude and duration of excess of post-exercise oxygen consumption between high-intensity interval and moderate-intensity continuous exercise: A systematic review. Obes Rev. 2021;22(1):e13099.
4. Harris MB, Kuo C-H. Scientific Challenges on Theory of Fat Burning by Exercise. Frontiers in physiology. 2021;12:685166-.
5. Shuster A, Patlas M, Pinthus JH, Mourtzakis M. The clinical importance of visceral adiposity: a critical review of methods for visceral adipose tissue analysis. The British Journal of Radiology. 2012;85(1009):1-10.
6. Brown JC, Harhay MO, Harhay MN. Visceral adipose tissue dysfunction and mortality among a population-based sample of males and females. Diabetes & Metabolism. 2016;42(5):382-5.
7. Klein S, Fontana L, Young VL, Coggan AR, Kilo C, Patterson BW, et al. Absence of an Effect of Liposuction on Insulin Action and Risk Factors for Coronary Heart Disease. New England Journal of Medicine. 2004;350(25):2549-57.
REFERENCES:
8. Vissers D, Hens W, Taeymans J, Baeyens J-P, Poortmans J, Van Gaal L. The Effect of Exercise on Visceral Adipose Tissue in Overweight Adults: A Systematic Review and Meta-Analysis. PLoS ONE. 2013;8(2):e56415.
9. Kolnes KJ, Petersen MH, Lien-Iversen T, Hojlund K, Jensen J. Effect of Exercise Training on Fat Loss-Energetic Perspectives and the Role of Improved Adipose Tissue Function and Body Fat Distribution. Front Physiol. 2021;12:737709.
10. Ismail I, Keating SE, Baker MK, Johnson NA. A systematic review and meta-analysis of the effect of aerobic vs. resistance exercise training on visceral fat. Obes Rev. 2012;13(1):68-91.
11. Wewege MA, Desai I, Honey C, Coorie B, Jones MD, Clifford BK, et al. The Effect of Resistance Training in Healthy Adults on Body Fat Percentage, Fat Mass and Visceral Fat: A Systematic Review and Meta-Analysis. Sports Medicine. 2021.
12. Ibañez J, Izquierdo M, Argüelles I, Forga L, Larrión JL, García-Unciti M, et al. Twice-weekly progressive resistance training decreases abdominal fat and improves insulin sensitivity in older men with type 2 diabetes. Diabetes Care. 2005;28(3):662-7.
13. Keating SE, Johnson NA, Mielke GI, Coombes JS. A systematic review and meta-analysis of interval training versus moderate-intensity continuous training on body adiposity. Obes Rev. 2017;18(8):943-64.
14. Steele J, Plotkin D, Van Every D, Rosa A, Zambrano H, Mendelovits B, et al. Slow and Steady, or Hard and Fast? A Systematic Review and Meta-Analysis of Studies Comparing Body Composition Changes between Interval Training and Moderate Intensity Continuous Training. Sports. 2021;9(11):155.
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