Why High-Intensity Interval Training Is Best For Weight Loss

If you want to lose fat (and not muscle) fast without doing hours of cardio every week, then you want to know more about high-intensity interval training.

Most of us learned at a young age that promises of “more for less” are usually a sham.

This is particularly true when we’re talking fat loss.

All we have to do, we’re told by shady supplement companies, is pop their pills and powders and we’ll be shredded in no time?


No amount of supplements can get you the body you want. In fact, most supplements can’t even help you get the body you want–they’re just completely worthless.

All we have to do, we’re told by shady exercise “gurus,” is spend a couple hours per week doing their workout routines and we’ll look like a Greek statue?


Getting into great shape may not be as complicated as many people think, but it requires that you get a lot of “little” things right ranging from caloric intake to macronutrient balance to progressive overload to training frequency and more.

“7 Minute Workouts” and fad dieting ain’t gonna cut it.

Now, if you’ve already heard of high-intensity interval training (also known as HIIT), you’ve probably heard a similar story: that it has near magical fat burning powers.

That you can do just a few minutes per day and watch fat melt off your body.


HIIT isn’t the alpha and omega of fat loss…but it can be a powerful weight loss tool when you know how to use it properly.

And that’s what we’re going to talk about in this article:

  • What high-intensity interval training is (and what it isn’t).
  • Why it’s great for fat loss.
  • Why it’s superior to low-intensity steady-state cardio for optimizing body composition.
  • How to do it right.

By the end, you’re going to know how to get the absolute most fat-burning bang for your sweaty buck.

What Is High-Intensity Interval Training (and What Isn’t)?

high-intensity interval training workouts

High-intensity interval training, or HIIT for short, is a style of exercising where you alternate between periods of (almost) all-out and low effort.

Hence, the name.

The high-intensity intervals push your body toward its metabolic limits (basically as hard as you can go) and the low-intensity intervals allow it to recover (catching your breath).

You probably already knew that, though, and have several specific questions, such as…

  • How “intense” do the high-intensity intervals need to be? How hard should you push yourself and how long should you go for?
  • How do the rest periods work, exactly?
  • How long should your HIIT workouts be?
  • How frequently should you do them?

Basically…how do you get the most out of individual HIIT workouts and out of your regimen as a whole?

Well, let’s find out.

How Intense Your High-Intensity Intervals Should Be

hiit routines

When you review scientific research on high-intensity interval training, you’ll see a lot of talk about something called VO2 max.

Your body’s VO2 max is a measurement of the maximum volume of oxygen that it can use, and it’s a major factor in determining your endurance level.

Its relevance to HIIT is this:

Studies show that you need to reach between 80 and 100% of your VO2max during your high-intensity intervals to reap the majority of HIIT’s benefits.

That’s nice to know but not very practical because it’s hard to approximate your VO2 max while exercising. There just aren’t reliable enough indicators to guess with any accuracy.

Fortunately, you can also work with a more useful metric: Vmax.

Simply stated, you’ve reached a Vmax level of exertion when you feel you can’t bring in as much air as your body wants (if you can comfortably hold a conversation, you’re not there).

For most people, this is about 90% of all-out effort.

1. Your goal during your high-intensity periods is to reach and sustain your Vmax.

That is, you need to get moving fast and long enough to make your breathing labored, and you need to hold that speed for  a fair amount of time.

As you can imagine, this means hard work. Think sprinting, not jogging.

2. Your goal during your HIIT workouts is to repeatedly achieve and sustain this Vmax level of exertion.

This might seem obvious, but it bears attention because the total amount of time you spend at the Vmax level of exertion determines the overall effectiveness of the HIIT workout.

That is, a “HIIT” workout that racks up maybe a minute of movement at Vmax level is going to be far less effective than one that accumulates several minutes.

Fortunately, this is just a matter of programming your workouts properly and not being a wuss when you do them.

We’ll talk about the workout programming soon and whenever you’re feeling wussy, here’s a friendly kick in the ass. 🙂

So, that’s “HIIT 101.”

Let’s now take a closer look at why we should choose it over easier, less stressful forms of cardio.

High-Intensity Interval Training and Burning Fat

high intensity interval training for cardio

Most cardio machines have pretty graphs that recommend you keep your heart range in middling “fat burning zone.”

If you do this, it’s claimed, you’ll maximize the amount of fat your body burns while you exercise as opposed to sugars.

Well, there’s a kernel of truth here.

You do burn both fat and carbs when you exercise, and the proportions vary with the intensity of exercise.

You see, research shows that as exercise intensity increases, so does the reliance upon muscle glycogen for energy over fat stores.

That is, as exercise gets more intense, the proportion of energy coming from glyogen stores becomes much larger than that coming from fat.

This is why a very low-intensity activity like walking taps mainly into fat stores, whereas high-intensity sprints pull much more heavily from carbohydrate (glycogen) stores.

These are the main reasons why many people think low-intensity steady-state cardio is best for losing weight.

Multiples studies such as those conducted by Laval University, East Tennessee State University, Baylor College of Medicine, and the University of New South Wales show otherwise, though.

Specifically, they show that that shorter, high-intensity cardio sessions result in greater fat loss over time than longer, low-intensity sessions.

What gives?

Well, let’s start with the obvious: total calories burned while exercising.

High-intensity exercise can burn quite a bit more calories than low-intensity exercise, and as fat loss is dictated by energy balance, the advantage here is clear.

Let’s say you jog several times per week and burn about 200 calories per session, with about 100 coming from fat stores.

When combined with a proper calorie deficit, those workouts will help you get leaner faster.

Better, though, would be high-intensity workouts of equal duration that burn, let’s say, 400 calories per session, with 150 coming from fat stores.

Diet notwithstanding, the workouts that burn the most energy are going to result in the most fat loss.

Energy expenditure while exercising alone doesn’t fully explain how just better high-intensity interval training is for losing fat, though.

A study conducted by The University of Western Ontario gives us insight into how much more effective it really is.

Researchers had 10 men and 10 women train 3 times per week, with one group doing 4 to 6 30-second treadmill sprints (with 4 to 6 minutes of rest in between each), and the other group doing 30 to 60 minutes of steady-state cardio (running on the treadmill at the “magical fat loss zone” of 65% VO2 max).

The results?

After 6 weeks of training, the subjects doing the intervals had lost more fat.

Yes, doing 4 to 6 30-second sprints burns more fat than 60 minutes of incline treadmill walking.

The exact mechanisms behind HIIT’s superiority aren’t fully understood yet, but scientists have isolated quite a few of the factors:

  • Increased resting metabolic rate for upward of 24 hours after exercise.
  • Improved insulin sensitivity in the muscles.
  • Higher levels of fat oxidation in the muscles.
  • Significant spikes in growth hormone levels (which aid in fat loss) and catecholamine levels (which are chemicals your body produces to mobilize fat stores for burning).
  • Post-exercise appetite suppression.
  • And more…

The science is clear: if your goal is to burn as much fat in as little time as possible, then HIIT is the way to go.

High-Intensity Interval Training and Your Muscles

high intensity interval training workouts

In most weightlifter’s minds, cardio and building muscle are pretty much antithetical.

You can have one or the other.

Again, there’s some truth to this, but it’s an over-simplification.

For example, research has shown that combining both strength and endurance training (concurrent training) can hinder your strength and muscle gains when compared to just strength training alone.

Studies have also shown that the longer your cardio sessions are, the more they impair strength and muscle growth.

That doesn’t mean that cardio directly impairs muscle growth, though. Because it doesn’t.

Too much cardio does.

The right amount of cardio, however, can actually accelerate muscle growth for reasons outlined here.

What is the right amount, then?

Well, there are two factors to consider:

  1. The duration of the individual cardio sessions.
  2. The total amount of cardio done each week.

And when the goal is optimizing body composition (which requires progress in the weight room), you need to keep your individual cardio sessions short and your total weekly duration relatively low.

Only HIIT allows you to fulfill these criteria and burn significant amounts of fat.

How to Create an Effective High-Intensity Interval Training Routine

high intensity interval training routine

So, chances are you’re ready for some HIIT in your life.

Well, there are five things you should consider when building a HIIT routine:

  1. The type of cardio.
  2. The length of the workouts.
  3. The frequency of the workouts.
  4. The duration and intensity of the high-intensity intervals.
  5. The duration and intensity of the low-intensity intervals.

Let’s look at each point separately.

The Best Types of HIIT Cardio

hiit exercises

HIIT principles can be applied to any type of cardio but some forms are more practical (and effective) than others.

Generally speaking, the three best choices are…

  1. Biking
  2. Rowing
  3. Sprinting

Biking and rowing are my favorites because sprinting is very hard on the legs and will likely interfere with your squatting and deadlifting.

The reason I recommend these three forms over others is research shows that the type of cardio you do has a significant effect on your ability to gain strength and size through weightlifting.

The long story short is this:

The more a cardio exercise mimics the movement used in muscle-building movements, like the squat or barbell row, for instance, the less it hinders strength and muscle growth.

This makes sense because one of the important parts of building strength is simply training a movement pattern repetitively. (The more you do a movement, the better you get at it.)

That said, if you can’t or don’t like to bike, row, or sprint, don’t be “afraid” of other forms of cardio such as swimming, jump roping, calisthenics, boxing, and so forth. They’re not going to whittle your muscle away.

Again, the big cardio mistake is simply doing too much.

How Intense Should Your Your High-Intensity Intervals Be?

high-intensity interval training program

The goal of HIIT is to go fast and hard, not slow and hard.

That means that if you’re using a machine like a bike or rower, you want enough resistance to pedal or pull against but not so much that it becomes a resistance training exercise.

That’s why the primary difference between high- and low-intensity intervals should be your speed, not the amount of resistance used. 

That is, you should increase and decrease resistance but not nearly as much as you increase and decrease your speed.

Now, as you know, the key factor that determines the effectiveness of a HIIT workout is the total minutes spent at a Vmax level of exertion.

If you spend too little time at this level, it’s a quasi-HIIT workout, and if you spend too much, you’ll burn yourself out.

Well, you achieve maximum time at Vmax by, when sprinting, going for that level of exertion as quickly as possible.

Don’t “build up to it.” Give each sprint everything you’ve got right out of the gate.

In terms of duration of high-intensity intervals, 50 to 60% of Tmax is sufficient if your goal is losing fat and improving metabolic health.

Tmax is simply the amount of time you can move at your Vmax speed before having to stop.

For example, I can bike at Vmax for about 3 minutes before my heart feels like it’s going to explode, so my Tmax is 3 minutes.

Therefore, my high-intensity intervals should be about 90 to 120 seconds long (and yeah, that’s hard!)

For your intervals, you can either test your Vmax (all you need is a stopwatch) or if you’re new to HIIT, start with 30-second high-intensity periods.

Your HIIT workouts should get progressively tougher.

The more you do HIIT workouts, the more your Tmax is going to increase. This means the duration of your high-intensity intervals will need to increase as well if you want to keep it maximally effective.

As you can imagine, these workouts can get pretty damn intense for experienced athletes.

In three HIIT studies conducted with highly trained cyclists, high-intensity intervals were 5 minutes long (and improved their performance). In contrast, other researchconducted with endurance athletes found that 2- and 1-minute intervals weren’t enough to improve performance.

How “Restful” Should Your Rest Periods Be?

high-intensity interval training for cardio

There are two ways you can make your HIIT harder:

  1. Increase the length of the high-intensity intervals.
  2. Decrease the length of the rest periods.

I generally recommend you first work on increasing the length of the high-intensity intervals until they’re in the range of 50 to 60% of your Tmax. This makes sure you’re doing true HIIT workouts.

Once you’ve achieved that, where you go from there is up to you.

I think it’s sensible to work rest periods down to a 1:1 ratio with the high-intensity periods (90 seconds of high-intensity work followed by 90 seconds of rest, for example), and then slowly raise the duration of both the high- and low-intensity intervals, maintaining that 1:1 ratio.

For example, let’s say you start your HIIT training doing 30-second high-intensity intervals followed by 60-second rest intervals (1:2 ratio).

As you continue, you get an idea of your Tmax and work your high-intensity intervals up to the 50 to 60% range, which comes out to about 60 seconds. You work at this level, maintaining the 1:2 high/low ratio (120-second rest intervals).

In time, you feel you can push harder and maintain the 60-second high-intensity intervals but start reducing your rest times, starting with 90 seconds (1:1.5 ratio).

Eventually your body adapts to this and you’re able to work the rest periods down to 60 seconds (1:1 ratio), and when even this isn’t challenging enough anymore, you start increasing both the high- and low-intensity intervals toward 90 seconds.

(And so on.)

You should also know that your rest periods should be active recovery, where you keep moving, not a standstill.

Studies have shown that active, not passive, recovery is advantageous for reaching Vmax during the high-intensity periods and eliciting the adaptive response to the exercise that we’re after.

How Long Should Your HIIT Workouts Be?

hiit cardio

One of the great things about HIIT is you get a lot out of what feels like little. There’s just no more efficient way to use cardio to drive fat loss and improve conditioning.

The big downside, however, is it can be quite stressful on the body, which means you don’t want to overdo it.

Do this, however, and you’ll be fine:

  1. Start your workouts with 2 to 3 minutes of low-intensity warm-up.
  2. Do 20 to 30 minutes of HIIT.
  3. Do 2 to 3 minutes of warm-down.

And you’re done.

There’s just no need to do longer HIIT workouts unless you’re focusing on improving performance, not losing fat.

If you feel you need more HIIT to lose weight efficiently, your diet is probably screwy.

How Frequently Should You Do HIIT Workouts?

hiit workout plan

The total amount of HIIT you should do per week depends on your immediate goals and what other types of exercise you’re doing.

If you’re looking to lose fat quickly, you don’t need to do more than 4 to 7 hours of exercise per week, and ideally you’d do more resistance training than cardio.

For example, my training and diet programs for both men and women prescribe just 3 to 5 hours of weightlifting and 1 to 2 hours of HIIT cardio per week.

This is how you lose fat and not muscle and maintain a healthy metabolism.