High-Intensity Interval Training: The Complete Guide

HIIT Guide

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Burning the maximum amount of calories in a minimal amount of time is a workout ideal that most of us can hop on board with. High-intensity interval training—commonly referred to as HIIT—is an increasingly popular workout due to this very notion. Think of it as the multi-tasking workout method of the fitness world—allowing you to burn an ample amount of fat, build muscle, and torch calories in less time than it takes to watch a rerun of Friends

Unfortunately, as the name implies, the workout is intense. Think bursts of hardcore, gut-wrenching exercise after exercise with brief rest periods in-between —and lots of burpees.

Before you sign up for a HIIT class or attempt to execute a workout at home, here is everything you need to know.

Meet the Expert

What Is HIIT?

Lauren Vickers
, Personal Trainer and Athletics Team Manager at F45 Training, a popular HIIT workout franchise, explains that HIIT is a classification of exercise which typically involves short intervals of high-intensity exercise, interspersed with static or active recovery periods. “This type of exercise is typically performed as a time-efficient alternative to steady-state aerobic training,” she explains.  

Dan Bowen, NPTI, NASM Personal Trainer and owner of Philadelphia’s Hit Fitness, who also specializes in the method, adds that most HIIT workouts will combine anaerobic exercises (those that do not use oxygen, like jumping) with and aerobic (those that involve oxygen, like walking). “One big advantage of HIIT is that you can gain maximal health benefits in minimal time,” explains Bowen. “You can get a fantastic workout in 20 to 30 minutes max and get the same benefits of a less intense one-hour or two-hour workout.”

In addition to torching an abundance of calories during your workout, Bowen points out that HIIT is one of the best workouts to promote after burn—the desired effect of continuing to burn calories long after your workout is over. It all has to do with the excess post-exercise oxygen consumption (EPOC) effect, he explains. “EPOC is a measurably increased rate of oxygen intake following high-intensity activity.” During the recovery process, the body restores itself to a resting state and adapts to the exercise just performed. This will include hormone balancing, fuel stores, cellular repair, and anabolism. “The EPOC effect is greatest soon after you are done exercising and decreases at a lower level over time,” he adds. 

Best For: Muscle Toning and Weight Loss

While HIIT is a great workout for anyone regardless of their workout goals, one of the reasons people endure the shorter yet rigorous workouts is because they can whip you into shape fast. “It is a great workout for leaning up, building lean body mass, improving cardiovascular health, and losing weight,” Bowen explains. 

While the amount of calories burned during a HIIT workout relies heavily on the length and intensity of your workout, one heavily cited study found that individuals doing HIIT workouts burned approximately 30% more calories during a 30-minute time period than those who engaged in other forms of exercise such as weight training, running and biking. And, taking into consideration that each 20-second intense exercise was followed by 40 seconds of rest, they also exercised for one-third of the time of the running and biking groups. 

What to Expect From HIIT Class 

You can do HIIT anywhere: your home, outside, at a gym, or even virtually. While there isn’t an exact formula to the workouts, they usually involve a combination of cardio/aerobic and resistance training. However, Bowen says you expect high-intensity, gut-wrenching bursts of hard work followed by short rest periods in between. 

He also points out that every HIIT workout class tends to be different, and many find its unexpected nature motivating. “Our days at F45 alternate between cardio, resistance, and hybrid, so the goal and style of training changes each day,” says Vickers.

Keep in mind that while HIIT classes are often tough, they are generally shorter than other classes your studio or gym offers. While the workout may be grueling, Bowen says the reward reaped at the end of class is worth it. “Going to a HIIT class is an exercise in extreme energy expenditure,” he explains. “As intimidating as it can be, nothing beats pushing yourself to your physical limits.”

Also, to avoid injury, he offers the following advice: “Don't overwork yourself, stay hydrated, and know your limitations.”

Benefits of HIIT

Vickers points out that there are many scientifically endorsed benefits to sustaining higher exercise intensities as a result of HIIT workouts:

  • HIIT Can Promote Efficient Calorie Burn: As previously mentioned, there is sufficient research supporting HIIT as one of the more effective workouts for calorie burn, allowing you to burn the maximum amount of calories in a minimal amount of time. 
  • It Can Help with Oxygen Consumption: As Bowen previously explained, HIIT workouts are effective in terms of oxygen consumption, helping your body continue to burn calories long after your workout is complete. 
  • It Can Help Boost Metabolism: Research also supports claims that HIIT can boost metabolism, increasing your metabolic rate hours after your workout. 
  • It Can Help Burn Fat: HIIT is one of the most efficient fat-blasting workout methods. One review of 13 studies involving 424 overweight and obese adults found that HIIT helped reduce body fat and waist circumference. Another study of overweight young men found that those who completed three 20-minute HIIT workouts per week lost 4.4 pounds in 12 weeks without making any changes to their diets. 
  • It Can Help Build Muscle: HIIT workouts can also help build lean muscle mass, says Bowen. 
  • It Can Promote Longevity: Due to its fat-blasting abilities and tendency to improve cardiorespiratory fitness, Vickers points out that HIIT can help prevent and improve a variety of health conditions, including decreasing the risk of diabetes, stroke, and certain cancers, as well as improving blood pressure, cholesterol, blood glucose levels, and mobility.
  • It Can Help Boost Mental Health: Vickers also notes that aerobic fitness increases have beneficial effects on psychological and cognitive outcomes such as decreases in depression and anxiety and increases vigor, cognitive processing, attention, and memory.
  • It Will Help with Daily Movement: Like other forms of functional training, HIIT workouts can increase your ability to carry out daily tasks and improve life quality, says Vickers. 

Safety Considerations

Since HIIT is a high intensity, full body workout, if you suffer from any injuries or preexisting health conditions, you should definitely check with your doctor first.  “Make sure that you get the go ahead from your doctor or physical therapist,” Bowen says. 

Additionally, because you will be doing lots of intense exercises in a short period of time, there is a risk of injury. “The most common injuries include a pulled muscle or torn ligament or tendon,” says Bowen. “Most importantly don't drive yourself into Rhabdomyolysis (Rhabdo)–a serious condition when you're exercising too hard and overexert yourself,” he says. 

Finally, he urges not to overwork yourself. “Stay hydrated and know your limitations.”


Similar to high-intensity interval training, low-intensity interval training involves intervals of exercises followed by periods of rest. However, as the name implies, the higher intensity periods aren’t quite as intense—and recovery times are usually longer. While HIIT workouts are a more popular method for experienced exercisers due to their ability to blast calories, LIIT can be a better option for beginners, seniors, those who prefer a lower intensity workout, or anyone suffering from an injury. They also involve less risk, as you are less prone to injury with a less intense workout. Keep in mind that you can still burn the same amount of calories doing a LIIT workout; however, you will have to invest more time. 

What to Wear to a HIIT Class

Like most workout classes, you should focus on wearing clothing that is comfortable and functional so that you can move in it. “You want something that can stretch and absorb sweat—because you're going to sweat your butt off!” Bowen says. “Also, find a pair of sneakers that you love that fit right to you. If your feet are uncomfortable, the rest of you will be too.”

“Bring a towel and water bottle, and get ready to sweat with the team,” adds Vickers. 


How to Get Started With HIIT

The most important thing in getting started with HIIT is to go at your own pace, Vickers points out. “It can be easy to get caught up in the excitement, music, and energy of the studio, but it’s okay to take it a little easier in your first few sessions while you’re finding your way,” she says. 

Also, make sure to ask your trainers for input—especially on how you can better your form, if you’re unsure of any exercises, or if you need a modification. “Trainers LOVE to assist people in moving better, getting fitter, and feeling stronger, so they’re always on board to help you get the best workout for your level,” says Vickers. 

Bowen offers similar advice. “If you are a beginner, get to know the basics first, get your form down and conditioning up,” he suggests. 

If you are taking a class in a fitness studio or gym, it is likely all the equipment you need will be provided. However, if you are at home, you can also reap the benefits of a HIIT workout—even if you don’t have weights or other equipment. “Just using your body as weight is fine and effective,” Bowen says. “You can use household items such as soup cans, water bottles, a gallon of milk, and if you're outside, tree branches, rocks, or use a hill to run on. There are so many options.”  

The Takeaway

If you are a non-disabled, results-driven individual who can embrace the “no pain, no gain” approach to fitness, then high-intensity interval training is the perfect workout. There is ample scientific research supporting HIIT as one of the most effective workouts on the planet, which is why it has become increasingly popular over the last decade. However, if you suffer from any preexisting conditions, prior injuries, or are of advanced age, it might be a little too intense for you. In that case, you should consider low-intensity interval training, a relaxed version of the amped-up workout. 


Article Sources
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