Everything You Need to Know About HIIT Workouts

Everything You Need to Know About HIIT Workouts

The fitness world is filled with trendy buzzwords, the most fashionable of which in recent years is probably “HIIT,” or “high-intensity interval training.”

But the concepts behind HIIT aren’t particularly new or trendy. They’re grounded in science and research, and they were around long before the snappy acronym.

That’s why they’re found in so many programs on BODi like INSANITY, 21 Day FixLIIFT4, Morning Meltdown 100, and Job 1.

LIIFT4 workouts

What Is High-Intensity Interval Training?

HIIT is any exercise style in which you alternate between short bursts of intense work and less intense recovery.

Of course, both “work” and “recovery” are relative to you and your fitness level.

“There’s no ‘best’ formula for HIIT,” says Trevor Thieme, C.S.C.S., BODi’s executive director of fitness and nutrition content. “The work-to-rest ratio depends on the activity, your fitness level, and your fitness goals.”

In general, though, you want to work at an intensity that doesn’t feel sustainable for very long; if you can speak even in short sentences during a work interval, you need to ramp it up.

And you want to work for a specified amount of time — usually somewhere between 10 seconds and a couple of minutes — that pretty much empties your tank.

Recovery intervals typically involve low-intensity activity (e.g., walking or jogging), the goal being to rest just long enough to bring your heart rate down and allow you to maintain a high level of performance during the work intervals.

Whether your goal is to lose weight, get healthy, or simply shake up your exercise routine, HIIT can be a game-changer.

Here are six benefits of high-intensity interval training you need to know.

HIIT Benefit #1: Burn Fat

Sure, increasing intensity is a great way to burn more calories during your workout.

But it can also help you burn more calories after your workout, Thieme explains.

This “afterburn effect” is known as excess post-exercise oxygen consumption (EPOC), and it’s a measure of your body’s increased calorie consumption post-workout as it goes about the repair, recovery, and adaptation processes.

Generally speaking, the harder you work out, the higher your EPOC will be.

That’s why a relatively short HIIT workout can ultimately burn as much (or more) calories than a longer steady-state cardio workout.

Still, when doing HIIT for fat loss, it’s important to remember that a boost in EPOC is only temporary, and studies disagree on exactly how long it lasts.

HIIT Benefit #2: Improve VO2 Max

High-intensity interval training is a great way to improve cardiovascular performance, says Justin Kompf, C.S.C.S., owner of First Guess Fitness, adding that it can be especially effective at helping you improve your VO2 max (i.e., the maximum amount of oxygen your body can utilize during intense exercise).

For the greatest VO2 max benefits, research suggests that HIIT workouts with three- to five-minute work periods might be your best bet.

LIIFT4 workout

HIIT Benefit #3: Build Muscle

You can add muscle strength to the list of high-intensity interval training benefits.

In a University of North Carolina study, participants significantly increased muscle size in just three weeks of high-intensity interval training.

That’s because HIIT emphasizes your type II muscle fibers—the same ones you target when you lift weights.

HIIT Benefit #4: Help You Stay Healthy as You Age

High-intensity interval training can also improve age-related decline in muscle mitochondrial function, according to a recent study in Cell Metabolism.

For all the non-scientists out there, mitochondria are structures in our body’s cells that perform several essential functions, one of which is to act as a “power plant.”

Mitochondria convert nutrients into a form of energy that cells can use to keep our bodies in good working shape.

Researchers explain that declines in mitochondrial capacity are a significant factor in the development of symptoms that we commonly associate with aging, such as wrinkles, frailty, chronic diseases, and overall poor health.

In the study, both cardio-based HIIT and HIIT combined with strength training packed similar aging benefits.

HIIT Benefit #5: Super-Efficient and Accessible

And here’s the kicker — HIIT scores you the benefits mentioned above in less time than other types of exercise.

So if you struggle to find an hour every day for the gym, maybe 15 to 30 minutes of HIIT might be more feasible.

Research actually shows that a 10-minute HIIT workout packs cardio benefits similar to a 50-minute sweat session.

Plus, while federal guidelines recommend people perform 150 minutes per week of moderate exercise, they also state that if you up the intensity, 75 minutes per week can do the job.

While a few kettlebells or dumbbells will definitely expand the number of exercises available to you, your body weight alone provides incredibly effective resistance.

High-Intensity Interval Training on BODi

To be clear, HIIT isn’t generally something beginners should jump into right away.

If you’re just beginning your fitness journey, work your way up to HIIT to avoid burnout and injury.

But once you’re ready for HIIT, you’ll find plenty of options on BODi, including these:

Transform :20

Is 20 minutes per day of exercise enough? It is with Transform :20, a high-intensity, six-week fitness program from Shaun T.

The only equipment you’ll need is a step — and no, this is nothing like old-school step class.


An efficient four-days-a-week program, LIIFT4 combines classic weightlifting and calorie-burning high-intensity interval training.

Morning Meltdown 100

The 100 workouts in Jericho McMatthew’s program feature different types of training, including HIIT, cardio, strength training, mobility, and more.

Each workout is 20 to 30 minutes and is set to the beat of a live DJ to keep you motivated.


In this MMA training-inspired program from Joel Freeman and Jericho McMatthews, you’ll punch, kick, and block your way through 30 days’ worth of sweat-drenching, high-intensity workouts.


The Shaun T program that helped popularize HIIT in the first place, INSANITY will test the limits of your endurance with extra-long work intervals and extra-short rest periods.

Foregoing weights in favor of bodyweight resistance, INSANITY workouts clock in at 40 to 60 minutes.

If you’re short on time, INSANITY MAX :30 limits each workout to 30 minutes.

For added muscle benefits, try INSANITY: THE ASYLUM VOLS. ONE and TWO. They require dumbbells, exercise bands, an agility ladder, and a speed rope.


Arguably the most widely known BODi program, P90X is all about high-intensity interval training workouts.

Using both resistance and bodyweight training, it’s designed to help you burn fat and build muscle in 90 days.

Already tried it? Check out P90X2 and P90X3 to switch things up.


Six days per week for 12 weeks, TurboFire rotates through 11 different high-intensity workouts, making you stronger, faster, and fitter every week.

Designed for intermediate exercisers, this program will take your total-body cardio conditioning to the next level.