It’s tough to read anything about fitness without coming across the term “HIIT” at some point. There’s a good reason why the acronym is so popular:

Research has shown that HIIT (short for high-intensity interval training) is hugely valuable for human health. And while HIIT isn’t the end-all-be-all for fitness, there’s a good chance your workout routine would be a lot more effective if you start incorporating this type of training into your regular program.

Keep reading to learn more what the science says about high-intensity interval training and how to get started with HIIT.

The Basics of High-Intensity Interval Training (HIIT)

Broadly speaking, high-intensity interval training (HIIT) is any workout that features alternating periods of short intense bursts of exercise followed by less intense bouts of exercise or “active recovery.” These intense bursts of exercise may be performed at an all-out effort (think sprinting) or at a slightly lower submaximal but still very intense effort (think running hard but not as hard as you can).

These short bouts of intense exercise can last as little as 45 seconds or less, or as long as 2 to 4 minutes. Any longer than that, a person wouldn’t be able to sustain the intensity level necessary to truly qualify as HIIT—imagine trying to sprint all out for five minutes!

The subsequent intervals of lower intensity recovery can vary considerably in length but are often performed in a ratio of work to the recovery of 1:1 or 1:3 or more. For example, if your interval of intense exercise lasts 30 seconds, you might recover for anywhere from 30 to 90 seconds before starting your next high-intensity interval. 

Start to finish, a full high-intensity interval training workout generally lasts between 5 to 20 minutes, depending on what you’re doing. 

As a workout methodology, HIIT isn’t new; research dates this type of training back to the early 20th century. These days, HIIT can be applied to almost any type of exercise modality—running, swimming, cycling, bodyweight movements like push-ups and squats, and even strength training movements using dumbbells or barbells. And while there’s no single recommendation, many fitness experts recommend performing two to three HIIT sessions per week in order to enjoy the optimal benefits.

This brings us to the next question: 

What are the benefits of High-intensity Interval Training (HIIT)?

HIIT and Weight Loss: What The Science Says

HIIT has a number of well-documented health benefits, but its ability to promote weight loss is one of its most well-known and sought-after effects. Here are a few scientific reasons why HIIT is so effective for helping people drop excess pounds:

• It helps you burn more calories during your workout. A 2015 trial published in The Journal of Strength & Conditioning Research determined that people who perform a HIIT workout burn more calories than they would during a steady steady cardio workout lasting just as long. 
• It helps you burn more calories after your workout. Oxygen debt, also known as excess post-exercise oxygen consumption (EPOC), refers to the increased amount of oxygen your body needs after a workout to produce energy (ATP) for your cells, repair muscle tissue, restore normal body temperature, and perform other important tasks that help get your body “back to normal.” As you might imagine, these tasks require energy, which means you end up burning more calories for a certain period of time even after you stop working out. And while HIIT may not increase your metabolism overall, it does appear to be better at creating an EPOC effect compared to low-intensity exercise, meaning it can temporarily give your metabolism a boost.
• It helps you lose body fat. A 2017 systematic review article showed HIIT can reduce waist circumference and body fat while improving body composition. A key reason is that HIIT promotes greater post-workout fat oxidation, meaning that your body ends up breaking down more fat cells for energy after the session ends. This is likely related to the fact that HIIT increases the release of certain hormones in the body that promote fat burning, including catecholamines and growth hormones.
• It improves blood sugar levels. Doing HIIT may help lower blood sugar and insulin resistance, both of which are associated with overweight and obesity.

Other than its superior ability to promote calorie burning and fat loss, HIIT has also been shown to do a lot of other good things for the human body, such as boosting muscle strength ¹, improving aerobic capacity, enhancing mood and mental health ², and lowering heart rate and blood pressure ³. These benefits seem to be the greatest in individuals who are overweight or obese, but anyone can benefit. Altogether, these effects can make HIIT an important tool in your chronic disease prevention toolkit!

Types of HIIT and How to Start

As mentioned, a HIIT workout can be performed using a near-endless variety of modalities and movements. HIIT workouts can be further classified into two main categories: cardio HIIT and strength training HIIT:

• Cardio HIIT: this is what most people think of when they hear about HIIT. It involves the use of classic “cardio” type movements such as running, rowing, cycling, swimming, or even bodyweight calisthenics like burpees, jumping jacks, or jumping squats. Here are a few ways people often choose to tackle a typical cardio HIIT session:
  • Tabata: this famous HIIT protocol involves 20 seconds of intense exercise followed by 10 seconds of rest, repeated 8 times—yup, that’s a 4-minute workout!
  • Every minute on the minute: at the start of each minute, perform a prescribed amount of intense exercise (e.g., a certain distance or number of repetitions), then rest the remainder of the minute. Repeat at the start of the next minute.
• Strength HIIT: for this type of training, a person may perform conventional resistance exercises, often with equipment such as dumbbells or barbells, while shortening the amount of rest taken between sets. 

No matter what type of HIIT protocol you follow, it’s important to precede any workout with a sufficient warm-up. This gets your heart rate up and your muscles and limbs warm, allowing you to get more out of the HIIT session while minimizing your risk of injury. 

Of course, given how beneficial HIIT seems to be, you might wonder whether you should bother continuing with steady-state cardio and conventional strength-training routines. The general rule: don’t forgo them! Longer duration aerobic exercise and traditional strength training are both beneficial and should be considered an important part of a well-rounded physical activity program. Plus, there are certain considerations that may make HIIT the less desirable choice over your other options. Check out some key advantages and disadvantages below:

Advantages of HIIT

• Very time-efficient—you can get equal or sometimes better results in less time than is required of a longer steady state cardio session (ideal for people with little time to spare!)
• Can be an effective routine for people who normally get distracted or bored with longer workouts
• Highly versatile
• Intensity level can be determined based on heart rate (typically, 80 to 90 percent of a person’s age-adjusted max heart rate) or on perceived exertion (by “feel” or how hard it feels like you’re working)
• Can be modified based on an individual’s rating of perceived exertion (RPE)—that is, “intensity” is relative to the individual’s current ability level and can be progressed gradually

Disadvantages of HIIT

• High intensity feels uncomfortable, so it may not be ideal or tolerable for certain individuals, such as people with lower pain-thresholds and people who are new to exercise
• May increase the metabolic stress and mechanical strain on muscles and connective tissues, potentially increasing the risk of injury or leading to more pain soreness
• May not be the most appropriate training methodology depending on an individual’s goals—e.g., if they are training for a long endurance race

Conclusion

Most doctors and health experts will tell you that any physical activity is better than none at all. To be a little more specific, the type of exercise you’re willing and able to consistently do is far better than the “trending” type of workout you dread and are likely to give up on.

That said, consider “hitting” a HIIT workout if you haven’t yet. You may find that the overall benefits of high-intensity interval training are well worth the temporary discomfort you feel during the actual workout itself—remember, it’ll be over before you know it! Just be sure to chat with your doctor if you’re brand new to exercise or if you’re currently being medically supervised for any reason

1. https://pubmed.ncbi.nlm.nih.gov/26479856/[↩]
2. https://pubmed.ncbi.nlm.nih.gov/31780128/[↩]
3. https://bjsm.bmj.com/content/51/6/494[↩]