T Nation

How Does HIIT Work?

Recently, I had to explain to a friend of mine why I was sprinting instead of just running around the track like everyone else. I got to the point where I had explained that intermittent sprints increase your metabolism for hours after the exercise, and then suddenly realized I was at a loss as to how or why this occurred.

“Metabolism” is a catch-word. What’s really burning calories after the exercise is over?

I really don’t want to start a HIIT vs. Steady State cardio argument. I’m hoping someone more knowledgable about biology and science can elucidate the mechanism that’s alluded to but never mentioned by studies on EPOC.

I always read bout EPOC and how great it is, but recently some authors have been saying that it is overrated.

I want to see how much more calories are burned during the session of HIIT itself vs a bout of SS cardio.

Plenty of people say that you shouldn’t get to HIIT if you’re low-carbing it, but it is also touted for fat loss, so it sounds like (implicitly) it is a good tool for minimizing fat gain during a bulk.

I wonder about the effects of a short HIIT session followed by 20-30 min SS cardio, or even a Tabata session then SS cardio…

The short answer, just take your heart rate every hour after you do steady state cardio and after HIIT. If you do the HIIT right, your HR should be higher for significantly longer. Your HR is a simple indicator of what is going on with your metabolism, it is your body’s tachometer so to speak. So when it is revved up, your are burning more calories.

Plus HIIT can actually build muscle (if you aren’t doing much weight training), can stimulate the type II MU’s so it is more useful for most athletics, many people find it more enjoyable, and it often takes less time, so it does have a lot of benefits (so does steady state but that is another topic).

What counts is results, which have been shown many times.

It probably isn’t truly known why, though things that appear to be possible explanations are known.

One, for example, is that GH release will be much more significant from the HIIT than from long-duration aerobics. So fat loss could be better for no reason but that, potentially.

As for calories burned during the exercise, it’s majoring on a minor, really.

As I think an article here recently put it, if you ask the average person who is leaner, a marathoner or a sprinter, almost everyone will wrongly answer “the marathoner.” Why, the marathoner burns more calories when he trains and when he competes!

Wrongo, they are not usually very lean. They burn up tissue all right but the body chooses to hold onto quite significant fat when undergoing their training protocol. It doesn’t choose to hold onto much fat when doing sprinting-type training. Regardless of what the reason may be. (It isn’t from sprinters being anorexics at the dinner table, btw.)

I’m hardly knowledgeable but my understanding is that along with EPOC, it also increases VO2 Max.

Sometimes I run hills for 2.5k working with heart rate at 95% for the steep sections and then run level and easy for another 2-3k. I don’t know what the actual effect is but since doing that and sprints regularly I notice a huge difference in my leg strength and I’ve gotten leaner. Previously I did daily SS cardio, with a weekly 10-13k run. I’m also needing to eat a whole lot more and sleep. According to my distances, I should be burning the same amount of calories but I’m eating waaaay more than I’ve ever eaten.

I need to switch to HIIT. I was doing it earlier this year.

Now, I can’t break a sweat with a 30 min SS cardio session at a decently high HR. Plus, I want to slit my wrists from boredom but then I’d have to wipe down the machine.

And who’d change the tunes on my music player? Dilemmas…

You need to run outside. It’s way more stimulating than the treadmill! Find a nice hilly route that’ll kick your ass. Rivers and bridges are fun too.

Everytime I think I’ve found my max heart rate I find out I’m wrong–it can go higher on hills.

there was some scientific study i saw once that compared two groups of men. 1 group did steady state, the other did HIIT. The steady state group burned way more calories, but the HIIT group had 9 times more fat loss. It’s much more intense so creates much more of an afterburn.

[quote]debraD wrote:
You need to run outside. It’s way more stimulating than the treadmill! Find a nice hilly route that’ll kick your ass. Rivers and bridges are fun too.

Everytime I think I’ve found my max heart rate I find out I’m wrong–it can go higher on hills.[/quote]

I prefer a nice rubber track. Plenty in my area.

I used to run wind sprints - jog the short ends (if you picture the track as a semi-rectangle) and sprint the long ends. I would warmup with a jog for the first lap, get in about 3 wind sprints, jog the next lap and walk one or two more for a cool down. Goal was 6 wind sprints but I never hit it.

Definitely more taxing outside…

Currently i am using this method for my cardio training at this phase of my workouts. I love it coz i HATE doing cardio all the time and i don’t have that much time on my hands given my career.

8 x 60 metre sprints 1 min 20 seconds between each. 2 times a week + weight training on seperate days.

If i can’t get outside, then 20 mins on an elliptical 30 secs on at high intensity, 30 secs off.

Every now and then I like having a good long run for fun and enjoyment. Balance is the key for me.

But if you ever wanted to make an argument about HITT vs. Steady State…look at the bodies of a sprinter vs. marathoner…which do you want?

I’m gonna leave that decision up to the audience as everyone is different.

How many people run marathons as their form of cardio?

Most good runners (not joggers) that I know are lean and fairly well defined but they run at a very fast pace. Most peoples steady state cardio sucks but running can be good for some.

HIIT can be excellent, especially for athletes but it is very tough to recover from if you are also lifting hard (at least at my age).

[quote]Zap Branigan wrote:
How many people run marathons as their form of cardio?

Most good runners (not joggers) that I know are lean and fairly well defined but they run at a very fast pace. Most peoples steady state cardio sucks but running can be good for some.

HIIT can be excellent, especially for athletes but it is very tough to recover from if you are also lifting hard (at least at my age).[/quote]

I remember trying cycle sprints the day after leg day. No dice. Way too much for me, and if it was the day before leg day, I didn’t have enough gas in the tank for the leg workout tomorrow.

See, I understand HIIT is ‘superior,’ but for something like CT’s “Regressive Ketogenic Diet” which he outlined in his Monday article, aren’t there just not enough carbs for HIIT to be a good energy systems workout while following that diet plan? Seems like SS cardio (fasted) would be the better option.

And I’m only saying this after reading from other members about how tough HIIT is without carbs. Even some authors have written this I think.

So what’s the compromise? When is HIIT the superior choice, considering diet?

Your statement that most people’s form of cardio is not running marathons each workout is true but doesn’t change the point.

The vast majority of those that do long-period cardio on the treadmill or bicycle, etc, not just those that run marathons, have quite substantially higher bodyfat than most that sprint.

Citing marathoners points out the result of the extreme, describes a clearly-defined set of people, and avoids the problem that some could say, with the above comparison, Well you’re comparing less athletic people with more athletic people.

The same point holds true with those that do long-duration aerobics that aren’t marathons.

Wanna lose muscle mass and start having serious trouble with further bodyfat loss at a much sooner point – or even “hit the wall” in that regard? Then use long duration, hard work aerobics not HIIT

Marathoners ~ long distance - is more about endurance then anything. Your lungs and heart and efficiently outputting enough energy through your muscles to maintain a pace.

Sprinting on the other hand requires controlled maximum output of the entire body. Done effectively the face goes slack and flaps in the wind ~ ever seen faces in wind tunnels? To sprint faster it takes a conscious ability to elevate energy and demand that your legs pump harder, faster, as you catapult down your lane ~ in turn swinging your arms faster helps to increase your speed ~ at the same time your core is working overtime to maintain balance and to ensure that the legs can pump away and the arms can pump away… Sprinting is primarily based on muscular power at maximum output.

  • The same mind muscle control that is noted in bodybuilding can be found in sprinting though with more skill and technique as your asking your entire body to work in-sync to go even faster and faster.

Kind of like chilling next to failure when your lifting weights. Similarly I think you can see the similarities between applying more force in the positive portion of a chest press. Or rapidly contracting your biceps when you are doing curls, hammer curls, etc ~

You are adding more pressure and resistance in terms of force. Due to velocity and acceleration ~

The same as if one person is trotting and a linebacker is going full speed and mach 1’s through the trotting slacker on the field. The linebacker will through velocity and acceleration output more force and go through his prey.

Sprinting isn’t a pyramid til you find your sweet spot, it is about extremes - where your body doesn’t operate at for the most part.

I ditto the wisdom of Roberts ~ There have been quite a few studies comparing GH gained from sprinting similar to squatting and dead-lifting.

From my perspective I won’t have my hip pop out when I’m pacing ~ but if I toss in max sprints without a few days of breaking myself in ( provided I haven’t been really pushing myself for a bit ) I can injure myself within the first 40 meters.

In sprinting your lungs are trying to shove as much oxygen as fast as possible to muscles that demand it.
Compared to - someone training intensely and trying to force as much air in and out every rep and then having to take some deep breathes between sets.

If this didn’t make any sense I apologize ~ Just thought I’d describe it from my point of view from prior experience.

In closing I hope the connections I made between lifting weights (veteran lifters should understand at least) and sprinting and noting that the most taxing lifts release GH like sprinting ~ there is your metabolism connection. Sprinting isn’t about endurance ~ it’s a muscular redlining of the entire system.

Propelling yourself against the air and fighting against gravity as you travel across a certain amount of space while time passes.

Since I’m always one to look at all the viewpoints: http://www.burnthefat.com/high_intensity_interval_training.html

It’d be interesting to see the discussion on this.

[quote]IronAbrams wrote:
Since I’m always one to look at all the viewpoints: http://www.burnthefat.com/high_intensity_interval_training.html

It’d be interesting to see the discussion on this.[/quote]

Good discussion ~ I’m a fan of NEPA walks and limited time engagement steady-state work. Along with taxing steady-state that is more muscular * hiking, stairmill from hell, tread-climber of sin. There is more then one way to skin the cat!

Sorry about taking this kinda off-topic but if we are currently in a x-week bulking program, is it wise to do sprints 2-3 times a week let alone any cardio at all? I’m concerned because I don’t want to get fat.

Let me tell you why I don’t fully buy the argument of “Well, just look at sprinters vs long distance runners.”

I had plenty of friends in track and do know that most sprinters tend to have better muscularity, however, I have not seen a ‘study’ where nutrition was taken into account.

I think most of us would agree that ‘a calorie is not a calorie.’ That said, I am curious if the long distance runner and sprinter had the same meal plan, and if the sprinter LOOKED better, maybe the diet was better suited for the sprinter’s physical activity, and better for building/preserving LBM?

If that is the case, then perhaps the long distance runner would need a different diet, different caloric intake and/or macronutrient breakdown.

It’s much more complex than to simply look at GH output and energy expenditure. There have been zero correlations with nutritional programs when comparing the anabolic/catabolic affects of steady state cardio vs HIIT.

How much of that is self-selection, though?

Remember when the OTC took some run times from Oly lifters. Oly lifters had greater start times than sprinters.

Does this mean oly lifting increases sprint time? Or that Oly lifters simply have a lot of type IIb fibers?

If you work with a jr. high track team, you’ll notice that most of the sprinters already have muscular physiques. They started off that way.

You’ll also notice that the young cross country kids have small physiques. Again, it’s not like they’ve been running hundreds of miles a week. It’s just what they got from the genetic lottery.

People choose sports that fit their types. It’s not the case that a sport makes someone a given type.

[quote]PonceDeLeon wrote:
Let me tell you why I don’t fully buy the argument of “Well, just look at sprinters vs long distance runners.”

I had plenty of friends in track and do know that most sprinters tend to have better muscularity, however, I have not seen a ‘study’ where nutrition was taken into account.

I think most of us would agree that ‘a calorie is not a calorie.’ That said, I am curious if the long distance runner and sprinter had the same meal plan, and if the sprinter LOOKED better, maybe the diet was better suited for the sprinter’s physical activity, and better for building/preserving LBM?

If that is the case, then perhaps the long distance runner would need a different diet, different caloric intake and/or macronutrient breakdown.

It’s much more complex than to simply look at GH output and energy expenditure. There have been zero correlations with nutritional programs when comparing the anabolic/catabolic affects of steady state cardio vs HIIT.
[/quote]

Well, all you need to do is train the way I suggested: do many hours per week of quite hard aerobic work.

Report back when you’re disgusted with how much harder it now is to get really lean and how much it’s interfered with lean mass.

Or if you think what I’ve written is not right, then hypothetically your outcome will be the opposite and you can report that.

In the meantime, maybe consider this:

Assume the body is fairly good at optimizing itself to what experiences teaches it is needed.

Now, if experience has been that frequently long hard hours of aerobic work are required, and this requires fat liberated from fat cells at a high rate for fuel, would the body intelligently drop fat stores quite low?

Or if experience is that the body frequently has need for maximal acceleration and maximum speed, and never needs a high rate of fatty acid supply for long periods of time, would the body intelligently hang onto substantial excess fat weight?

Isn’t it conceivable anyway that the body might optimize itself to the experienced needs? And it’s optimal, in terms of being able to meet the demands, for someone doing long hours of hard aerobic work to have plenty of capacity to supply fatty acids to the bloodstream?

Or just do the experiment. Countless people already have (usually inadvertently, except when deliberately when first learning of HIIT, and then doing the comparison in the opposite direction) and so the results are generally known already, but there’s nothing like doubters finding out for themselves via personal experience.