High intensity interval training (HIIT) has been praised as the ultimate fat burner for more than two decades, since the mega bestselling Body for Life lauded it as the greatest way to shed fat from your frame. As it turns out, HIIT may have some fat loss benefits, but not for the reasons most commonly professed. No alien technology involved.
The erroneous assertions about HIIT always had to do with caloric burn. Allegedly, those who do HIIT burn way more calories during, and even way more calories after the exercise through the metabolism staying revved up. Years ago, I reached out Bill Phillips, author of the aforementioned Body for Life, to ask what research such assertions regarding the fat burning properties of HIIT were based on (his book didn’t provide references). After getting his response I began to pick it all apart in a column for the Los Angeles Times that showed there was no caloric burn difference between HIIT and steady state cardio – either during the exercise or in the time following – if the amount of “work” was the same in the same period of time. I’ve also written about HIIT for AskMen when exposing the bad math of OrangeTheory fitness.
The idea of HIIT keeping your metabolism massively elevated for hours after the exercise is over has been blown apart. Caloric “after burn” never amounts to much regardless of the exercise employed, and the better cardiovascular shape you are in, the lower the after burn is going to be, because your heart and breathing go back to normal quickly.
Let’s compare HIIT to steady state: I can run at 7.5mph for an hour and cover, well, 7.5 miles. Duh. That’s steady state; same pace throughout (more or less). Alternatively, when doing intervals, I’ll do a slow warm up for about half a mile, then go all out for two minutes then slow for two minutes alternately for about 50 minutes, followed a final half mile of slow to cool off. Doing those near barf-inducing intervals I’ll also cover almost exactly 7.5 miles in one hour. The average speed of that interval-training run was also 7.5mph, and thus the exact same amount of work was completed by my body in the same total time. Note that “in the same total time” is important.
And so, the same number of calories were burned both during and after those runs whether it was via HIIT or via a steady pace. Because science (see previous links for references).
But wait! Didn’t I say that HIIT could be good for fat loss? Well, yes, I did, and it can, if you realized it’s the stoned frat boy explanation and not the let’s drag Mulder and Scully out of retirement explanation.
Before we get into that, let’s go a little beyond the whole “want to burn fat” aspect of HIIT and look at some other cool reasons to do it, because realistically, HIIT is much more than a “one weird trick” for fat loss.
HIIT is about performance enhancement. Those who engage in it do so to improve their performance in a host of sports. I used to it as part of my training to PR in both the 10K and the marathon. Because it’s great for making you better at short bursts of activity, it can also be good for sports like basketball and hockey, and I’ve found that when I was training for that 10K PR my ability as a downhill skier was much improved as well. Overall, HIIT increases the body’s lactate threshold, increases maximal oxygen consumption, increases maximal aerobic speed and power, as well as changes mitochrondial number and function, enzyme activity and energy stores in the muscle cells.
It can also cause injury and burnout if you do it too frequently. Twice a week is good. One potential problem with HIIT is that it can be so exhausting it causes you to couch sit the rest of the day, meaning fewer calories burned than if you did a steady state workout followed by some non-exercise activity.
Let’s finally talk about the fat loss properties, because HIIT can work for losing fat. Here is the non-alien invader explanation as to why:
For some, HIIT is the only type of cardio they’ll ever do
Lifters love to bash cardio, and specifically running. Articles abound how cardio kills gains, kills kittens, kills you … For a certain subset of those who love the iron, they will never just go for a run, but the idea of HIIT can be appealing for them, adding in a not insignificant caloric burn to their exercise regimen. Note that calling it “cardio” is a bit of a misnomer (see previous link), as HIIT is considered both aerobic and anaerobic.
The HIIT, after they get good at it, can make them better at lifting as well, enhancing both their muscle-building capabilities and their caloric burn during their lifting sessions. Yes, HIIT has been shown to also enhance muscular hypertrophy, but when compared to the size-gaining benefits of a challenging lifting regimen, comparing HIIT to the iron is like comparing a .22 rifle to a .50 cal. You don’t need HIIT to get big.
HIIT can suppress appetite
Anecdotally, I’ve found that a hard HIIT session can have significant effect on appetite, in that it makes you not want to eat. I’m not saying it promotes starvation, but we live in a society where we’re continuously surrounded with hyper-yummy treat food, and resisting the Kentucky fried grease blobs gets tiresome, so we eat. As a review of the research published in Appetite showed, high intensity exercise has a hormonal effect that dampens desire to eat, making it easier to stick to a (wisely) calorically restricted dietary regimen that allows for sustainable fat loss.
However, it doesn’t just have to be intervals specifically to get this benefit. I’ve found that a hard and fast steady run that does the same total work, as described earlier, has the same appetite suppressing effects of interval training. Slow cardio doesn’t seem to do it, but fast cardio, whether via intervals or steady state, makes chips, chocolate and ice cream a lot less compelling.
You can add to this the “alternative reward” aspect of HIIT. An intense workout hits the same reward centers in the brain that does things like treat food and alcohol, so you’re less likely to desire it in the first place, and if you do consume it then the reward sensation is blunted because you already got your “fix” via exercise.
HIIT makes you a bad ass
“Lean bodies are made in the kitchen.” – Me, said too many times to count. I suppose you could say they’re made by staying out of the kitchen, but the reality is that it’s people who prepare their own meals rather than eating out who are more likely to be successful with weight loss.
The hardest part of weight loss isn’t the hour or so you train each day, but the food you both do and don’t stuff in your face hole the other 23 hours of the day.
Interval training is hard. There are a variety of ways of implementing it, but I’ve described it as the longest two minutes of your life, followed by the shortest two minutes of your life, followed by the longest two minutes …
Sticking to a healthy, calorie-controlled diet is also hard.
Those long two minutes of interval training are brutally exhausting and mentally taxing. It takes a badass to persevere. It isn’t the legs making you go; it’s the brain telling the legs to go. And as you get better and better at intervals, you don’t just make your body stronger, but the mind becomes stronger as well.
And a strengthened mind is one that can stick to the diet required for sustained fat loss.
James S. Fell, MBA, CSCS, is an internationally syndicated fitness columnist for the Chicago Tribune and Los Angeles Times, and author of Lose it Right: A Brutally Honest 3-Stage Program to Help You Get Fit and Lose Weight Without Losing Your Mind, published by Random House Canada. He is head fitness columnist for AskMen.com, and a contributor to Men’s Health, Women’s Health, the Guardian, TIME Magazine, and NPR.