HIIT is better than cardio: science or placebo-effect?

Everyone’s saying that interval/HIIT cardio–e.g. running 10 sec fast, 10 sec slow, etc–is superior to steady-state. They say it burns more calories during workout AND for 1-2 days after. I’m skeptical; this is too magical, like click-ads that say “Use this one technique and have a perfect life”. Wouldn’t it be easy for HIIT to sound to someone like “add periods of intense sprinting to your workout” and this would get them to work harder in GENERAL and this is why they’re really losing more calories? Could HIIT just be a mental technique to get you to work harder?

Who are “they”? It depends on the workouts. A particular LISS cardio session can burn more than a particular HIIT session and vice-versa.

It’s said to burn more calories (by some sources up to 48 hours) through post-exercise oxygen consumption (EPOC). That can be measured, so we’d know if higher calorie expenditure was just occurring during exercise.

There is evidence that more intense exercise sessions increase EPOC:


So for us non-athletes, what’s most relevant is calories burned during exercise. Studies differ, and are cherry-picked for sensationalism in exercise magazines, but the majority lean to that conclusion.

Not 100% clear on the question - Intervals are part and parcel of performance training and have been for decades - you do them if you want to get faster / better at the sport in question, and their value is not in doubt.
You seem more interested in their role in weight loss? Not sure about that - I’d be very sceptical of consistently doing HIIT as a general approach to weight loss as it would be way too hard on the body. A proper red zone interval session will fold you in half - something you work into structured training alongside easier workouts. Strong people can do them quite regularly but (nowadays) will be monitoring their training load so they don’t get excessively fatigued. The out of shape should definitely be taking small steps with HIIT and not trying something way out of their league that they read on the internet.

On the other hand, just jogging or cycling at a steady pace for hours can get boring. So even if you’re not interested in competition it’s good to work some structure in

In a scientific environment you could have subjects do steady and HIIT workouts and monitor their calories, but that doesn’t always translate to real world results. The problem is that most humans get bored with the monotony of a long steady workout. Even if steady workouts burns significantly more calories, that may not matter if the person gets bored and slacks off or quits working out entirely. So even if it was just a mental trick to fight boredom, that would be immensely important in terms of overall exercise benefit.

However, competitive athletes will do whatever workout is necessary to give them the results they need. If steady workouts gave them the best result, they would do that and deal with the monotony by having the coach yell at them to keep going.

But for us normal folks, the most important aspect of exercise is creating the motivation to keep doing it. If dancing in Zumba classes means the person leaves with the smile on their face and excited to come back, that may be the most important aspect for weightloss. The fact that they could have burned more calories doing XYZ activity may be irrelevant if they would have quit working out because they got bored. So although there may be a scientific answer to your question, a regular person will be best off doing an exercise they will do consistently over time.

In my personal experience, HIIT workouts are more interesting and engaging. The shorter bursts of activity keep my motivation up, while steady workouts tend to have my mind wander to thoughts of quitting. I can do an hour HIIT workout and not feel the time, while 20 minutes on the treadmill feels like a lifetime.

One reason for the additional calories afterwards is that the high exertion level gets your body to a place where things break down and trigger your body to repair and build stronger. If you go for a walk, your body does not get stressed enough to need to repair anything. But if you sprint, you put greater strain on your body, which your body will attempt to address. Or if you lift a light weight, you don’t stress your muscle enough to trigger it to grow even if you lift the light weight a lot of times. But if you lift a heavy weight a few times, your muscle fibers are stretched and stressed enough to tell your body to build more muscles. Then over the next day or two, your body is creating more muscle fibers, which takes calories to do.

No, it’s not.

The OP is talking about HIIT cardio. Aside from any minute “gainz” a beginner would see, it’s not very relative to calorie expenditure over time.

The current science on HIIT is that it might be better than “regular” training but the measured differences are so small that it only really matters for Olympic-caliber athletes (and wannabes). It is far far more important that you exercise than the type of exercise.

As a personal testimonial, HIIT did far more for my resting pulse and stamina than steady state aerobics.

I’ve done four hours a week of steady state. And I’ve done 50 minutes a week of HIIT, of which only eight minutes was actual high intensity exercise. The other 42 minutes were warm-ups, cool downs or intervals between high intensity intervals.

That eight minutes a week of high intensity exercise did more for me than when I did four hours a week of steady state.

THis thread could probably could do with some definitions or we’ll be mired in bolloxology like this - HIIT only making differences to olympic-caibre atheletes. The number of amateur athletes who successfully interval train to get faster must outnumber Olympians 1000-1. It is the principal way to get faster / stronger, for anyone, once you’ve reached a natural base level of fitness. So actually the ‘measured differences’ in performance are so large it’s not even a question.

OTOH if we’re talking about the benefits of HIIT to those not overly interested in performance, who do low / med intensity exercise as part of good health regime and are looking at HIIT because there are some signs up at the gym - that is more questionable. Certainly as a supplement to easy sessions it makes sense, in fact it’s textbook, but one of the biggest challenges of a heavy interval training block (on the bike IME) is not getting ill with colds etc - they are taxing on the body. All intensity all the time is just a recipe for illness and (if you really do a lot), over-training which can bury you for months. So obviously it’s all in the approach, but a sensible quantity of intensity mixed in with easier stuff sounds right for most people.