Quick Hit Summary

People have long been told that if they want to lose weight, they must incorporate at least 30 minutes of aerobic exercise into their daily routine. However, there appears to be a more time efficient style of training for individuals looking to lose those love handles. Recent research indicates that high intensity interval training (HIIT), which involves 4-10 repeats of running, swimming, cycling, etc, at maximum intensity for 30 seconds followed by a 4 minute rest interval, is just as effective as 30-60 minutes of jogging for fat loss. There is one caveat worth mentioning; For HIIT to be effective means of fat loss, one must train at MAXIMUM intensity.

High Intensity Interval Training (HIIT)

Figure 1 Is there a more efficient way to lose fat than jogging for 20-30+ minutes a day?⁹.

Infomercials… is there one thing that provides more comic relief than some of these ads? I especially like the exercise equipment ads that shows a stunningly good looking model with a tight body who happens to be advertising a device that aided him/her lose 15-20 lbs of fat. All it took was using this random exercise device for ONLY 10 MINUTES A DAY, 3x A WEEK! I think the most recent training device I saw promoting these benefits was a shaking/vibrating stick type of device that people held out in front of them.

Call me overly skeptical, but I doubt many of these magical exercise devices are all they’re cracked up to be. It’s long been established that continuous endurance training (CET) is the preferred method of training for those looking to lose weight. Heck, according to the National Institute of Health, we must exercise 30-60 minutes a day, 5-6 days/week for weight loss¹. I’m sure everyone has heard this dogma from various health authorities. However, within the last 10 years many individuals in the sport and fitness community have come forward claiming that a more time efficient method of training may exist. No, it’s not one of those sketchy late night infomercial devices. Rather, it’s a form of exercise referred to as High Intensity Interval Training (HIIT). For those not familiar with HIIT, it involves running, swimming, cycling, etc, at MAXIMUM intensity for 10-30 seconds followed by a 0.5-4 minute rest interval. Depending on the goals of one’s training program, this process is then repeated 4-10 times.

So does HIIT really work? Is exercising at a high intensity for ~ 3 minutes a day truly as effective as 30-60 minutes of CET? To answer these questions lets turn to the research.

HIIT and Fat Loss

The research on HIIT and fat loss ceased to exist prior to 2000. However, within the last 5-10 years various studies have demonstrated that HIIT can be an effective means to assist with fat loss. The ability of HIIT to increase the body’s ability to burn fat occurs relatively soon. For instance, both Perry et al. and Talanian et al. demonstrated that 2-6 weeks of HIIT improves ones capacity to burn fat during subsequent aerobic exercise²³. Additionally, Whyte et al. found that only 2 weeks of a HIIT cycling protocol improved resting fat oxidation by 18% in 10 sedentary men (mean age- 32.1 years; mean BMI- 31)⁴.

As discussed above, HIIT enhances the body’s ability to burn fat. However, the two studies mentioned above were relatively short in duration (2 weeks). Furthermore, they do not provide any evidence as to if HIIT is more, less or of equal effectiveness as CET with respect to weight/fat loss. Luckily for us, both of these topics were addressed in a recent study completed by Macpherson et al⁵. In their study, 20 healthy, recreationally active individuals (12 men, 8 women; mean ages – 22 to 24 years; mean body fat- 18-20%) were randomly assigned to complete 6 weeks of either a HIIT or CET treadmill running program as described in Table 1. [For reference "recreationally active" was described as 11 ultimate Frisbee players, 9 university students. Also, no significant differences were present between groups with respect to these variables (ie – % body fat, etc) at the start of the study.

Table 1 Training routines of individuals participating in Macpherson et al. study. For the HIIT protocol, ACTIVE REST (ie – walking, etc) was encouraged between each bout of max intensity running⁵.

Prior to the start of the study, no significant differences in age, weight, or body composition were present between groups. Upon conclusion of the study, these anthropometric measurements were reassessed. Results indicated that despite training for only 1/18th of the time that those in the CET group did, 13.5 hrs vs. 0.75 hrs over the entire trial, individuals in the HIIT experienced similar decreases in body fat. As seen in Figure 1, those in the HIIT lost 12.8 % of their original body fat whereas those in the CET lost 5.8% of their body fat. This difference between groups was not significantly different from each other from a statistical point of view.

Figure 1. Percent decrease in body fat after 6 weeks of HIIT or CET. Please note, although those in the HIIT experienced a greater % decrease in fat mass vs. the CET individuals (12.8% vs. 5.8%), the difference was not deemed statistically significant.

A couple quick words of caution when evaluating the results of this study… Individuals in the HIIT (or CET) group did not go from 18% body fat to 6% body fat. Rather they lost 12.8 % of their original body fat mass, causing their % body fat to drop from 18.4% to 16.6%.

According to Dr. Peter Lemon, one of the contributing members of the MacPherson et al study, their research team is currently finishing up a study that looked at the effects of 6 weeks of HIIT on fat loss in a group of 15 women¹⁰. Once again, those participating in HIIT experienced significant decreases in fat mass vs. baseline values. However, it’s premature to say that exercise alone was the sole reason for this fat loss as dietary records are yet to be fully analyzed. Via personal communication with Dr. Lemon, I was informed that…

"Essentially, with treadmill SIT [editor's note – SIT stands for sprint interval training] in a larger group of adult women, we found similar training improvements in VO2max and performance as the MacPherson study but also observed body fat loses. A quick look at the dietary records (which we’re inputting now) appears to indicate that decreases in energy intake do not explain the fat losses. This suggests that the energy expenditure of the sprint interval training is responsible. This is consistent with another recent study where we measured VO2 during and for 24 hours following a SIT session vs an endurance session. Despite observing a greater VO2 during the endurance bout, 24 hour oxygen consumption with SIT was equal or greater, i.e., oxygen consumption following SIT stays elevated for some time and this appears to be important from a weight loss point of view…¹⁰"

How Can One Work Less but Burn More Fat?

UPDATE JULY 13, 2013 As mentioned in this post, originally it was thought that the results seen in these studies were related to EPOC. However, since originally writing these pieces, I've come across a fair amount of research that suggests that while the effect does exist, the magnitude of it is smaller than originally hypothesized. I refer you to my friend Adel Moussa's discussion on this subject matter.

After reading the above study, I’m sure you’re waiting for me to say “gotcha” or something similar. How can one lose just as much body fat using HIIT compared to exercising 18x longer while ET? I’ll be honest with you; at face value this does not make sense. I can state with almost 100% certainty that those completing CET burned more calories while exercising than those in the HIIT Group. However, as suggested by Macpherson et al. & Dr. Lemon, individuals in the HIIT likely burned more calories during the non workout hours in a phenomenon known as Excess Post-Exercise Oxygen Consumption (EPOC). For those not familiar with EPOC, it refers to the energy expended by the body to recharge itself following an intense anaerobic training session. This energy is believed to be spent replenishing ATP & phosphocreatine stores, converting lactic acid (produced via exercise) into glucose and restoring blood hormone levels⁶. This phenomenon is not observed to nearly the same extent following aerobic training sessions⁷.

Other Benefits of HIIT

Sport Performance

The benefits of HIIT extend far beyond simple fat loss. As discussed in my article High Speed Interval Training for Improved Sport Performance, HIIT is a far superior form of training for ball/strength/speed athletes vs. CET. Rather than rehash that entire topic, I encourage you to read that article for more information on the topic. Also, if we're just looking at the "aerobic" spectrum of performance, Macpherson et al. also found that HIIT was equally as effective for improved 2000 meter time trial performance (HIIT —> 4.6%, CET—> 5.9%) and VO2 ( HIIT—> 11.5% , CET—> 12.5%) in their sample population.⁵

Cardiometabolic Health

HIIT also improves various cardiovascular factors. Rakobowchuk et al. completed an interesting study in which 20 healthy individuals (10 males, 10 females; BMI 23-24, Age- 23 years) were assigned to either HIIT or CET cycling programs for 6 weeks⁸. See Table 2 for specifics of the training protocol. Following the training program, it was found that a HIIT cycling protocol was just as effective as CET with respect to improving peripheral arterial stiffness (popliteal artery) and flow-mediated dilation. In other words, HIIT improved peripheral blood vessel (popliteal) function equal to that of CET.

Table 2 Training protocol utilized by Rakobowchuk et al.⁸

Improved cardio-metabolic functions have also been observed in overweight and obese individuals following only 2 weeks of HIIT⁴. Whyte et al. observed that insulin sensitivity improved by 23.3% and systolic blood pressure decreased 4.7% in sedentary men (BMI- 31) following only 2 weeks (6 sessions) of HIIT. For reference, the HIIT protocol involved cycling at max intensity for 30 seconds followed by a 4.5 minute rest interval.

Am I bashing endurance training?

Thus far, I’ve provided evidence that HIIT is equal to or superior than continuous aerobic training for fat loss, cardio-metabolic health and ball/speed/strength sport performance. On a cautionary note, PLEASE do not misinterpret the point of this article. I am NOT trying to bash endurance training. Rather, my goal is to shed light on a more time efficient manner to improve the aforementioned variables. If you happen to one of those individuals who are truly passionate about endurance running, cycling or swimming, more power to you. I think that’s awesome and I applaud your commitment.

Bottom Line

There are many ways that one can go about improving body composition. For the individual looking to lose weight, continuous endurance training is often the popular choice. However, recent research indicates that high intensity interval training may be a more time efficient method of weight and fat loss. Thus, if you only have a short time frame to work out, tone down the endurance training and start sprinting!

And before I forget, HIIT is much more physically demanding than regular aerobic work and thus, greater risk of injury is involved with it. Thus, be wise and don't start sprinting at high speeds if you have trouble walking >20-30 minutes (or similar) pain free!

References

¹ National Institute of Diabetes and Digestive and Kidney Diseases. Physical Activity and Weight Control. NIH Publication No. 03–4031. March 2010. Accessed July 1, 2010 from: http://win.niddk.nih.gov/publications/physical.htm#control_weight

² Perry CG, Heigenhauser GJ, Bonen A, Spriet LL.High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle. Appl Physiol Nutr Metab. 2008 Dec;33(6):1112-23.

³ Talanian JL, Galloway SD, Heigenhauser GJ, Bonen A, Spriet LL. Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women. J Appl Physiol. 2007 Apr;102(4):1439-47. Epub 2006 Dec 14.

⁴ Whyte LJ, Gill JM, Cathcart AJ. Effect of 2 weeks of sprint interval training on health-related outcomes in sedentary overweight/obese men. Metabolism. 2010 Feb 11. [Epub ahead of print]

⁵ Macpherson RE, Hazell TJ, Olver TD, Paterson DH, Lemon PW. Run Sprint Interval Training Improves Aerobic Performance but Not Max Cardiac Output. Med Sci Sports Exerc. 2010 May 13. [Epub ahead of print]

⁶ Powers SK & Howley ET. Exercise Physiology: Theory and Application to Fitness and Performance. 5th ed. New York: McGraw-Hill. 2004. 53-55. Print

⁷ Laforgia J, Withers RT, Shipp NJ, Gore CJ. Comparison of energy expenditure elevations after submaximal and supramaximal running. J Appl Physiol. 1997 Feb;82(2):661-6.

⁸ Rakobowchuk M, Tanguay S, Burgomaster KA, Howarth KR, Gibala MJ, MacDonald MJ. Sprint interval and traditional endurance training induce similar improvements in peripheral arterial stiffness and flow-mediated dilation in healthy humans. Am J Physiol Regul Integr Comp Physiol. 2008 Jul;295(1):R236-42. Epub 2008 Apr 23.

⁹ Photo taken by U.S. Air Force Photo/Staff Sgt Araceli Alarcon. Accessed June 13, 2010 from: http://en.wikipedia.org/wiki/File:Treadmills_at_gym.jpg

¹⁰ Lemon, Peter. "Re:Sprint Interval Training vs. Endurance Training on body composition." Message to Sean Casey. July 13, 2010.