Everything You Need to Know About HIIT Workouts

The fitness world is prone to trends and buzzwords, the most fashionable of which in recent years is probably “HIIT,” short for 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 fashionable acronym.


What Is HIIT?

Simply put, HIIT is characterized by short bursts of intense work interspersed with brief moments of rest. You should follow a program developed by fitness professionals and you’ll definitely need to be willing to step outside of your comfort zone.

“Intense” is relative to each person’s fitness level, but you should be working at a pace that doesn’t feel sustainable for very long; if you can speak even in short sentences during a high-intensity interval, you need to ramp it up.

There’s no standard time associated with HIIT workouts, but most work intervals range from 10 seconds to a couple of minutes. Rest intervals also vary in length and type.

Some workouts prescribe complete inactivity between work sets, while others call for low-intensity exercise or active recovery, like walking, stepping in place, or light jogging.

The rest period is typically just long enough to allow for partial recovery, but not long enough to allow your heart rate to return to its resting state.

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

There are dozens of HIIT variations, but the variation most people are familiar with is Tabata, a 4-minute workout that includes eight consecutive rounds of 20 seconds of work followed by 10 seconds of rest.

EMOM, another formula that’s popular among trainers and group fitness instructors, calls for a specified number of reps “every minute on the minute,” with the rest encompassing however many seconds of each minute remain.

And if you’re grinding through an AMRAP, your goal is to complete “as many reps as possible” within a specified amount of time to complete a “round,” resting as little as possible between rounds.

All of these templates can be applied to almost any type of exercise, including cycling, running, rowing, and resistance training.


7 Benefits of HIIT Workouts

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

1. They burn crazy calories

According to Thieme, you’ll burn tons of calories both during and after you work out — for up to 48 hours. Sometimes referred to by trainers as the “afterburn effect.” This phenomenon is known as “excess post-exercise oxygen consumption,” or EPOC.

To investigate the effects of EPOC, a team of researchers from East Tennessee State University studied two groups of clinically obese women. Both groups exercised on treadmills — one did “low-intensity steady state” running (aka jogging) while the other did high-intensity interval training.

While neither group experienced a reduction in body weight during the eight-week study, the high-intensity group ended up slimmer. That’s important, because it means the women in the HIIT group changed their body composition, losing significant amounts of fat while gaining enough muscle (which weighs more than fat by volume) to keep their scale weight steady.

Much of that fat loss likely came from the effect of HIIT on their resting metabolic rates: After each workout, the metabolisms of the women who performed HIIT were nearly four times higher than those who did lower-intensity exercise — and they remained higher for up to 24 hours.

2. They save time

Time, or lack thereof, is one of the most commonly cited obstacles to starting and maintaining an exercise routine.

Between family and work obligations, the average person struggles to find an hour for the gym. But 30 minutes of HIIT a few times a week is much more feasible.

3. Cardiovascular strength

According to the Centers for Disease Control and Prevention (CDC), that half hour of HIIT is not only efficient, but it also offers the same health benefits as an hour of cardio performed at a slower rate.

The CDC’s guidelines recommend that all adults accumulate at least 150 minutes of moderate-intensity exercise every week.

But you can trim that down to 75 minutes if you bump up the effort to “vigorous-intensity” exercise. You’ll receive all the same health benefits — including a stronger cardiovascular system — but in half the time.

4. Improved VO2 max

VO2 max is the maximum amount of oxygen your body is capable of consuming during high-intensity exercise. It’s a helpful measurement for athletes in training, but it’s also a good indicator of general fitness.

HIIT has been shown to help increase VO2 max by pushing your body to work at full capacity for short intervals.

5. Muscle gain

Because most people are tight on time, they may find themselves choosing to do either cardio or resistance training, but not both. Inevitably, their goals for muscular development or cardiovascular health and endurance suffer.

Because you can add resistance to HIIT — whether that’s through free weights or body weight — you can derive both cardiovascular and muscle-building benefits from one workout.

6. They’re cheap

Most HIIT workouts can be performed with little to no equipment, which means you don’t have to pay for a gym membership or empty your checking account outfitting a home gym.

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

A simple, fast-paced circuit of push-ups, lunges, squats, and sit-ups will get your heart pumping in a matter of minutes.

7. You can do them anywhere

Since there are so many bodyweight HIIT options, you can stick to your training plan even when you’re on vacation or traveling for work.

If your hotel doesn’t have a gym, head outside or clear a small patch of hotel room floor, set the timer, and get to work.


Who Should Do HIIT?
hiit workouts

If you’re just beginning your fitness journey, or it’s been a while since you worked out with any regularity, you should work up to HIIT.

“If you jump into HIIT without first building a solid foundation in fitness, you increase your risk of overtraining, which can hamper your progress and even sideline you with an injury,” says Thieme.

A personal trainer can put you on the right track, designing programs that are appropriate for your current fitness levelOver time, you can progress through increasingly intense programs until you’re ready for HIIT.


How to Get Started Doing HIIT Workouts

With HIIT, it’s easy to get too much of a good thing — even if you’re ready for it — because the workouts are intended to push the limits of your strength, stamina, and grit.

“That’s why if you’re new to HIIT, you might want to consider first doing a program that contains HIIT workouts, but doesn’t focus on HIIT exclusively,” says Thieme.


How Often Should You Do HIIT?

Once you’re ready for a dedicated HIIT program, start slowly. “Don’t go all-in right away — ease into it by keeping your intensity dialed back for the first few workouts to avoid overreaching, overtraining, and/or experiencing excessive exercise-induced muscle soreness,” says Thieme.

“But if you’re following a smart workout program designed by a smart trainer who knows how to push your limits without compromising your safety and recovery, you can perform HIIT multiple times a week,” he adds.