High-intensity interval training, more commonly known as HIIT, has skyrocketed in popularity during the last decade. It’s a very effective and time efficient method for boosting cardiovascular fitness in previously untrained folks, and it’s also been shown to nudge VO2max higher after it has stalled in trained athletes.
That HIIT training can provide significant aerobic and anaerobic fitness benefits is beyond doubt, which is why it’s now included in the training programs of a wide variety of high level athletes.
It’s the effect of HIIT on body composition where things get a little foggy. When a training modality has allegedly produced fat loss from workouts lasting as little as 12 minutes, it’s almost begging to be hyped by every huckster wanting to exploit the public’s perennial desire for a quick, sure-fire fat loss “secret”. Hence the plethora of idiotic “Lose all the fat you want with only 10 minutes of exercise a week!” claims you see plastered all over the Suckernet.
So what’s the real story? Is HIIT all it’s cracked up to be for fat loss, or is it just another overhyped load of cobblers?
Sprint On, Sprint Off…
Most of you by now have heard about the HIIT protocol of Japanese researcher Izumi Tabata, which entered the Western consciousness in a big way after the now-defunct Muscle Media magazine wrote a glowing article about it back in 2001 (you can read the original article here). The Tabata protocol involves a four minute warm-up at 50% of max effort, followed by a series of 8 balls-to-the-wall 20-second sprints, each separated by a 10 second “active rest” where you (try to) pedal at the same pace you did during the warm-up. After the last sprint, you cool down with another four minutes of 50% effort, before jumping off the stationary bike, puffing your chest, and crushing a can of Solo against your head.
One thing that should be pointed out about Tabata and just about every other HIIT protocol that has been subjected to peer-reviewed research is they were performed on cycle ergometers – that’s the scientific term for what’s more commonly referred to as a stationary bike. This is worth noting because there are ‘Tabata’ routines on the Internet utilizing everything from sprint running to rope flailing to front squatting. There’s nothing wrong with mixing things up for a little variety, but don’t even begin to expect the same kind of cardiovascular benefits from front squat “intervals” that you’ll get from trying to emulate Anna Meares on an ergo bike.
Normally I’d post a picture of a top male sprinter like Shane Perkins or Chris Hoy. But when you can emulate the 145kg squat and turbine-like pedaling action of 2012 Olympic Gold Medalist Anna Meares, come back and then we’ll talk about Shane and Sir Chris. The girl’s an absolute dynamo.
Dodgey Extrapolation Strikes Again
The other thing that should be pointed out about the Tabata research is that, even though it was used to launch the “HIIT = amazing fat loss!” craze, it never actually examined fat loss.
What it did do was compare the aerobic and anaerobic conditioning effects of the Tabata HIIT protocol with steady state cardio, then later with another HIIT routine involving longer active rest periods.
Nonetheless, reports of markedly boosted EPOC (excess post-exercise oxygen consumption) from HIIT had the marketing-minded fitness ‘gurus’ tingling with excitement. After all, when your concept of the ‘scientific process’ is finding what gimmicks will garner the most blog hits and book sales, there’s nothing like a little EPOC to help you spin wild tales to potential customers about how their metabolisms will go into turbo-boost and how they’ll be able to burn off bucket loads of ugly fat simply by doing a few minutes’ exercise a few times a week.
If this all sounds reminiscent of the MAD charlatanism brought to us by the not-so-friendly folks at Low Carb Inc., well…it is. However, unlike the MAD bollocks, there is actually a kernel of truth in the HIIT EPOC story. But only a kernel.
From this wee kernel sprouts the observation that if you compare a high intensity and low intensity activity – matched for work output – the former will usually produce a greater EPOC than the latter.
But in real life, this scenario is not always applicable. There seems to be a simplistic belief - eagerly perpetuated by those who apparently don’t know better yet still deem themselves fit to act as authorities on the subject - that there are only two types of cardio: HIIT and steady state. You’re either intermittently sprinting your brains out, or you’re plodding along at a dead steady pace on a gym treadmill while watching Entertainment Tonight in a trance-like state for 45 minutes.
This of course is nonsense, as just about anyone who’s watched a real life sporting event would know. Real-life cardiovascular activities are often undulating or erratic in their intensity, whether it’s the running bursts that characterize on-field ball games, or the greatly varying terrain of a typical road cycling stage.
Tell me – if you do eight twenty-second sprints on an ergo, or jump on a real bike and ride in the hills for 90 minutes at a fast clip, and include a few Marco Pantani-inspired moments where you attack a steep section with extra pep, do you honestly believe the brief HIIT session will cause the greatest EPOC? Only if you’re MAD; the reality is your work output was in fact much, much higher during the 90-minute ride.
The late, great Marco “Il Pirata” Pantani.
The reality is that EPOC is not just affected by exercise intensity - EPOC increases linearly with the exercise duration. The research so far indicates that while exercise duration affects only the duration of EPOC, intensity seems to affect both EPOC magnitude and duration. Meaning that, if an exercise session is both long and intense, as is actually quite common in many sports, then you’ll end up with an EPOC that will dwarf that to be garnered from the 5-minute Super Dooper Flab-Busting Fat Furnace workout that Joe “I never met a Reciprocal Marketing, Affiliate-Chasing, List-Expanding opportunity I didn’t like!” Blogger has convinced you is the Rosetta Stone of fat loss training.
And here’s another fundamental but vitally important factor to be considered: In a best-case scenario, EPOC will account for a couple hundred extra calories burned up to 48 hours after a workout. Even if we pretend that long duration cardio doesn’t raise EPOC, it still overpowers HIIT for overall calorie burn.
Given that a brief HIIT-style workout might burn up to 250 calories, but a fast-paced ride in the hills or intense sparring/rolling/bag work can see you incinerating calories at the rate of 1,000 per hour, and will typically last at least 90 minutes and often more…do I really need to go on?
As I have stated countless times on this site and in my book The Fat Loss Bible, fat-derived weight loss is all about calories.
Calories, calories, calories, calories, calories, calories, calories, calories, calories, calories, CALORIES!
Damn I love that word. In fact, I absolutely adore it because every time I mention it some angry reality-hating low-carber out there who earnestly believes he/she knows more than me (and folks like Jules Hirsch and George Bray) about fat loss - despite the fact he/she is built like a girdle-wearing hippopotamus - is guaranteed to suffer a self-induced aneurism.
Look, there goes another low-carber!
OK, enough funnin’…back to the topic at hand: Calories! It bemuses me to no end to see people trying to devise all manner of clever routines that will somehow send their metabolism off into the stratosphere and burn fat like butter in a fry pan, and yet ignore the most fundamental equation that underlies every successful fat-derived weight loss attempt:
CALORIES IN MUST BE LESS THAN CALORIES OUT.
In terms of body weight maintenance, your body doesn’t give a brass razoo whether you do Tabata squats before or after burpees, or whether you complete the Crossfit Mary-Lou-Betsy-Jo routine in 3.45, or the Stella-Marie-Rosie-Jane routine in 4.01. It only cares if, over a sufficient period of time, you’ve burned off significantly more calories than what you’ve ingested. It’s at this point your body will think, “Oh shit, energy shortage!”, pick up the hotline to Bob down in Fat Dispatch, and relay with a sense of urgency, “Bob, we got a situation – for some reason we’ve got a lot less calories coming through, and now I’ve get every damn mitochondria in the place calling me up in a panic, pissing and moaning they don’t have enough energy. Do me a big favour and unlock the fat stores, will ya?”
And, as I discuss at length in The Fat Loss Bible, therein lies a big problem with studies examining the effect of exercise programs on fat loss: They rarely factor in the overriding importance of calories. If you conduct a clinical trial and tell the obese participants to walk 3 times a week, or you give them a more vigorous program but simply tell them to keep eating as normal, what do you think is going to happen?
Yep, they’re going to lose bugger all weight because in the first instance the calorie burn is simply insufficient, and in the second instance there’s absolutely nothing to stop the participants from using typical Western logic and thinking, “Gee, I’m training so hard now, I reckon I deserve an extra donut…or three!”
And then someone who shall remain nameless but whose name rhymes with Gary Taubes will seize the opportunity to garner a lot of attention for himself and his latest book by appearing on talk shows alongside Oz Memet loudly proclaiming “exercise is useless for fat loss!” and that the only reason folks like Lance Armstrong are so skinny is not because they spend six hours a day pedaling with serious intent on a bike but because they were just plain old born that way.
Never mind that professional athletes quickly put on weight out of season or after they retire if they don’t keep a lid on their food intake (see my article here on what happened to the greatest cyclist of all time when he retired but kept eating like he was still competing).
Lance Armstrong: “I'm on my bike, busting my ass six hours a day. What are you on?” Well Lance, I’m on a ketogenic diet endorsed by jokers like Gary Taubes, Jimmy Moore and Michael Eades that elevates my cortisol levels, drains me of vital minerals, and gives me such an amazing fat loss metabolic advantage I’ve managed to gain another fifty pounds of chub while sitting on my ass attacking people who tell the truth about calories. Pretty cool, huh!
The fact is that when the participants of exercise studies are confined to a ward situation, where their food intake can be controlled, the addition of exercise invariably results in extra fat loss than the group/s performing no exercise. Meaning that if you acknowledge the calories in versus calories out equation, the addition of exercise to your fat loss regimen will speed things up nicely. And not only will you lose more fat, with the right kind of exercise you’ll also keep more muscle…and maybe even put on some, as we’ll discuss shortly.
The bottom line is that if you are trying to design an effective fat loss program that will take you from overweight to jaw-droppingly lean, you sure as hell better acknowledge the primal role of calories.
Either that, or go buy yourself a girdle.
Alright Anthony, But What About HIIT?
If you’ve made it this far, you’re probably on the edge of your chair with suspense, wondering whether HIIT is a fat loss HIT or whether it’s just a load of SHIIT (sorry, couldn’t resist that one). Either that, or things are real quiet at work.
So without further ado, here is a quick(ish) look at the surprisingly sparse research examining the effect of HIIT on fat loss.
In a fifteen-week study by Tremblay et al comparing Canadian men and women who performed either HIIT or lower-intensity stationary cycling, little overall weight change was noted in either group. However, the HIIT exercisers reportedly experienced more favourable body composition outcomes, with a greater mean reduction in skinfold measurements taken at six different body sites.
As is unfortunately par for the course in these types of studies, dietary intake was not controlled. But clearly the subjects in both groups ate sufficient calories to maintain weight on their assigned routines. On the surface, this would suggest that while HIIT did not affect overall weight loss it can have superior "repartitioning" effects on body composition by preserving muscle and shedding a little extra fat instead.
Despite the lack of overall weight change, the skinfold results saw to it that this study was cited far and wide as ‘proof’ that doing HIIT is akin to packing your fat cells with dynamite.
Unfortunately, this study had some discrepancies that preclude us from placing too much faith in the results. To determine body fat changes the researchers used only skinfold measurements, which are not as accurate and consistent as underwater weighing, DEXA (dual-emission X-ray absorptiometry) and MRI. While much has been made about the HIIT group’s threefold greater reduction in combined skinfolds, a close look at the skinfold data shows the reduction in abdomen skinfolds was virtually identical between the two groups.
And while most of the steady-state group’s skinfolds either stayed the same or decreased, their limb and calf skinfolds increased. Either this group were biological freaks who could lose fat in one area but gain it in another, or there were inaccuracies in the skinfold measurements. Given the known problems with skinfold reproducibility (variations between testers and even with the same tester due to differences in skinfold measurement technique), I’d put my money on the latter.
From Quebec to Sydney: HIIT and Fat Loss in Aussie Women
In a more recent study conducted down here in what all my American friends refer to as “Oss-stray-lee-ya”, a bunch of fellow “Ossy” women aged 18-30 with a mean body mass index of 23.2 were randomly assigned to one of 3 groups: HIIT, steady-state exercise, or control. The HIIT and steady-state groups each trained for 15-weeks. Meanwhile, the control group continued to sit on their dimpled butts eating low-fat muesli bars watching Home and Away, Neighbours, and all that other incredibly banal brain-numbing pap that constitutes prime-time soap opera TV in this here sunburnt country.
The average energy expenditures during the HIIT and steady-state sessions were 199 and 193 calories, respectively. As with the previously discussed study, there was no dietary intervention; all subjects, including the exercise groups, were instructed to continue their normal eating habits throughout the study. Sigh.
At the end of the study, cardiovascular fitness had improved significantly in both groups, but only the HIIT subjects experienced fat loss. The HIIT group experienced a mean 1.5 kg total weight loss and a 2.5 kg fat loss over the 15 week period. The steady-state group lost 0.1 kg of weight and gained 0.4 kg of body fat, while the control group gained and 0.3 kg of body weight and 0.4 kg of fat.
Other findings of note were that the fat loss effect of HIIT was greatest in the obese participants and far less pronounced in the women who were already lean. The HIIT group also enjoyed far greater reductions in resting insulin levels, indicating superior improvements in glycemic control. This may simply have been an artefact of the greater weight loss in the HIIT group (weight loss itself often produces notable improvements in glycemic control).
So in this study, HIIT did indeed produce a greater fat loss than steady-state training. But given the similar energy expenditure between the two training regimens, a greater calorie burn during training did not explain the difference.
The long-term effects of exercise intensity on appetite are unknown; in short-term studies, higher intensity exercise has been shown to reduce, maintain, or even increase post-workout caloric intake compared to lower intensity exercise[3-5]. In this study, it would appear the HIIT regimen may have blunted appetite more effectively than the steady-state routine. Or maybe the HIIT subjects really did experience some serious EPOC - but we'll never know because it wasn't measured.
For those of you wanting to replicate the results of this study, it should be pointed out that the HIIT routine consisted of eight-second sprints followed by 12 seconds of slow pedalling. No problem, you say? Yeah, but this wasn't your usual 6-8 sprints - the HIIT subjects performed sixty of these sprints each session!
Hey, where did everyone go?
Hot Off the Press: HIIT and Fat Loss in Aussie Men
Now listen up, you lot - the above study only involved women and here in Austraylia the blokes don’t like to be confused with sheilas (except in Darlinghurst). No bloody way. That is fair dinkum un-Australian (all-encompassing Aussie catch-phrase, especially popular with vote-seeking politicians and pious Prime Ministers, for any kind of behaviour that causes offense). Because only a dimwit drongo who’s as dumb as a dead dingo’s donger would extrapolate research results from the ladies to the fellas, the aforementioned researchers had another crack of the HIIT whip, yelled “Coo-eee!!” and this time rounded up a bunch of fat bastards to pedal their arses off in one of those big fancy bloody sheds where they do all that you-beaut fancy bloody research stuff.
And what did they find this time, I hear youse all asking?
Strewth! Jumpy little wombats, aren’t yers? First I have to explain what these researcher blokes and their subjects actually did, and then reveal the results. There’s a natural progression to these things, ya Wallies! So sit your fat bums back down, grab a coldie, put ya feet up, and let me bloody well finish.
[Clichéd Aussie lingo section officially ends here. For now.]
Here’s what transpired in the second study, which was recently released ahead of print. Forty-six inactive, overweight men were recruited from the University of New South Wales and allocated into either HIIT exercise or non-exercising control groups. Unlike the previous study with women, there was no longer-duration-lower-intensity cardio group. The exercisers and controls were similar in age (24.7 and 25.1 years) and BMI (28.4 and 29). Five subjects later withdrew from the exercise group and three from the control group. Bloody slackers!
As for diet, subjects in both exercise and control groups were advised to maintain their normal eating habits during the study. You know, the usual free-living carry on; unfortunately, metabolic ward trials are quite expensive and funding these days tends to be diverted to far more important things like conducting yet more dodgey studies that are halted early to give the impression statin drugs work in healthy people. There’s also the problem of recruiting sufficient people who are prepared to temporarily give up their incredibly fulfilling and exciting lives of Facebooking, tweeting and watching Internet porn to instead go live in a ward and make a meaningful contribution to science.
So here’s my solution: Start a reality show called HIIT Shores, recruit a bunch of horny Italian-American kids with a fondness for hair gel, confine them to a specially-equipped metabolic ward for the duration of the show, and tell them they can run amok so long as they eat 2,500 calories per day and do three sessions of HIIT per week. Compliance? Don’t worry, I already got that figured out: Get caught doing extra exercise or eating smuggled cannoli then, yo, this constitoots a sit-choo-way-shun and you get yo ayass booted off da sho. No more nookie with Snooki, you stoopid palooka. The only other rules are no Galliano, Sambuca or Jägermeister within 3 hours of training, and no wearing Abercrombie & Fitch hahaha.
Um, anyway…back to Sydney. The HIIT group once again performed 8-second sprints interspersed by 12-second bouts of slow pedaling. They did this continuously throughout each 20-minute session, which was performed 3 times weekly for 12 weeks.
For all you fellow detail geeks types that love getting lost in the specifics, the HIIT sprint workload was set at 80–90% of each subject’s heart rate (HR) peak at a cadence between 120 and 130 rpm and recovery was set at the same amount of resistance but at a cadence of only 40 rpm. As subjects adapted to the HIIT training, workload was increased so that HR stayed at the appropriate 80–90% peak level.
The average HR during the HIIT training sessions was 160 ± 9 beats per minute, which corresponded to 88% of peak HR.
Now THIS is sprinting...
Okay, so what happened by the time week 12 rolled around?
Not surprisingly, HIIT resulted in a measurable increase in cardiovascular fitness with absolute VO2peak being increased by 13% and relative VO2peak by 15%. In other words, their lungs could now perform at a given workload with noticeably less huff and puff than 3 months earlier.
Total body mass decreased in the exercise group by 1.5 kg (2%), whereas total fat mass decreased by 2.0 kg. The fat mass of controls was unchanged after 12 weeks. And while greater fatness often predicts greater fat loss in dietary intervention weight loss studies, and also predicted greater fat loss in the earlier trial with women, in this trial initial percent body fat in the men was not correlated to changes in percent body fat after the HIIT intervention (and unlike the earlier female study, this trial saw no changes in measures of insulin or insulin resistance. And you thought I was kidding when I said only a dimwit drongo who’s as dumb as a dead dingo’s donger would extrapolate research results from females to males. Tsk tsk).
As for fat-free mass (which includes precious muscle), the HIIT group experienced a 1.2kg increase. The earlier study with females found trunk lean mass was increased by 0.6 kg after 15 weeks of HIIT.
The Bit Where I Sum Everything Up and You Mutter “Why Didn’t He Just Say That at the Start?!”
Okay, here’s the nitty gritty of everything we know about HIIT and fat loss so far:
Despite the massive amount of hype and wankology that has been built up around the alleged “fat furnace!” effects of HIIT, very little research has in fact been done on this topic, and the only two studies reliably showing actual fat loss involved routines featuring 60 x 8-second sprints.
This is a far, far higher number of sprints than what you’ll find in other HIIT routines, yet fat loss amounted to only 2-2.5kg over a 12-15-week period. While that’s certainly better than a kick in the bum with a studded boot, it hardly constitutes an earth-shattering, fat-obliterating outcome.
To keep things in perspective, after three months BMI in the men went from 28.4 to 27.9, and percent bodyfat went from 34.8 to 32.8. So the participants started the study overweight, and finished the study overweight. It was a similar scenario for the women in the earlier trial; their mean trunk BF% started at 36.5% and dropped to 33.2%.
With higher volume exercise and judicious calorie restriction, 0.5-1.0kg per week weight losses, comprised mostly of fat, are not at all unrealistic. But that would be with a damn sight more exercise than 60 minutes a week, and with a conscientious effort to consume a predetermined level of calories, one that would allow for a sufficient calorie deficit to occur.
For those of you wanting to get that lean athletic look, under 10% for men and around 15% or under for women usually does the trick. So what the above studies show is that a few 20-minute HIIT workouts a week is simply not going to be sufficient to get you there if you are presently carrying a serious amount of flab. Without accompanying caloric restriction nor any additional longer-duration exercise, the 200-calorie per session calorie burn of a brief HIIT session is simply not enough to produce the kind of fat loss that will produce noticeable changes in your appearance, regardless of any accompanying EPOC.
Keep that in mind the next time you hear some Infomercial-brained “guru” banging on about how you can lose all the fat you want with just a few minutes of exercise each week.
And while the shameless marketers of intermittent fasting, low-carb and super-slow training books will rush to accuse me of shameless marketing for mentioning this, I explain in a fool-proof (but not sub-moron-proof...sigh) fashion how to set up a fat loss regimen encompassing all of the aforementioned factors in The Fat Loss Bible (and may I add all proceeds from the sale of this book are donated directly to the Hey Ho, Let’s Grow! Feed Ramone the Dog with the Hugest Appetite in Australia Fund).
100% of proceeds from the sale of this book go to a very worthy cause: Satisfying my dog's caloric needs.
HIIT is also the cardio of choice for folks who are trying to gain muscular weight. If you’re a hard-gainer, you’re going to make gaining muscle a heck of lot harder again if you’re chewing up the extra calories you need for growth with 2-3 hour cardio sessions. Brief, explosive forms of cardio will not just permit muscular gain, they will quite likely enhance it (see legs of speed skaters and top track cycling sprinters for convincing visual evidence of this phenomenon).
Anyways, I hope youse all enjoyed my take on the current state of HIIT fat loss research. If not, youse can all get stuffed!
Under normal circumstances, AnthonyColpo.com would apologize to Australians and Italian-Americans for any offence caused by this article. However, the author is himself Italian-Australian, so just harden up, you pack of bloody sooks.
- Børsheim E, Bahr R. Effect of exercise intensity, duration and mode on post-exercise oxygen consumption. Sports Medicine, 2003; 33 (14): 1037–1060.
- Tremblay A, et al. Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism, Jul, 1994; 43 (7): 814-818.
- Trapp EG, et al. The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. International Journal of Obesity, 2008; 32: 684–691.
- Thompson DA, et al. Acute effects of exercise intensity on appetite in young men. Medicine and Science in Sports and Exercise, Jun, 1988; 20 (3): 222-227.
- Pomerleau M, et al. Effects of exercise intensity on food intake and appetite in women. American Journal of Clinical Nutrition, Nov, 2004; 80 (5): 1230-1236.
- Ueda SY, et al. Comparable effects of moderate intensity exercise on changes in anorectic gut hormone levels and energy intake to high intensity exercise. Journal of Endocrinology, Dec, 2009; 203 (3): 357-364.
- Heydari M, et al. The Effect of High-Intensity Intermittent Exercise on Body Composition of Overweight Young Males. Journal of Obesity, 2012. doi:10.1155/2012/480467
- Boudou E, et al. Absence of exercise-induced variations in adiponectin levels despite decreased abdominal adiposity and improved insulin sensitivity in type 2 diabetic men. European Journal of Endocrinology, 2003; 149 (5): 421–424.
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