What is HIIT? The workout that burns fat fast and builds fitness

Imagine if there was a way you could instantly boost your mood, focus and metabolism — all while burning a bunch of calories and improving your cardiovascular health? While unfortunately, there's no magic bullet that achieves all of this, there is a quick, free and not-so-easy solution by the name of 'HIIT.'

Chances are, you've heard of this popular exercise style —whether it's in the form of 'Tabata' training or the burgeoning HYROX trend taking over gyms. HIIT is popular for a reason: it's a fast, effective and functional training approach that can provide reliable results.

But what does HIIT actually involve, and how does it differ from other types of cardio? Plus, is it beneficial for everyone — or just some people? Read on for everything you need to know.

What is HIIT?

Popularised in the 1970s by personal trainer Arthur Jones, HIIT stands for 'high intensity interval training.' The training protocol involves alternating between short, sharp periods of effort and periods of low-intensity recovery or rest. It's really this 'interval' approach that defines the HIIT format, and differentiates it from other training styles.

HIIT workouts actually have their original roots in 'fartlek' or 'speed play' in the 1930s, when Scandinavian runners used them as an alternative to traditional endurance training. However, HIIT doesn't necessarily have to involve doing sprints on a treadmill or track. You can do it just about anywhere, with any type of equipment (or none at all!)

What are the benefits of HIIT?

High intensity training has been associated with many physical, mental and overall health benefits. Firstly, it's been found to help regulate blood pressure, even more effectively than moderate intensity continuous training [1]. In one study,  6-weeks of HIIT training reduced blood pressure by around 3–5 mmH in overweight and obese men, with similar results also seen in women [2,3].

Studies also show that HIIT is the most effective type of cardio for improving several metabolic health markers [4]. This includes improving blood sugar, cholesterol levels, lipid profiles and body fat.

Then, there are the benefits for your brain. A recent meta-analysis showed that high-intensity interval training leads to moderate improvements in mental health, mood changes and perceived stress [5]. Studies also show that HIIT training can improve your concentration, memory and focus — making it perfect for before a big workday [6]. Plus, because HIIT is all about maximum effort, you're going to leave your local gym with a strong sense of achievement and satisfaction.

High-intensity exercises also help to build your agility and cardiovascular fitness [7]. Even short HIIT sessions have been found to significantly increase VO2 max (how efficient your body is at using oxygen) [8]. In other words, the more aerobic interval training you do, the fitter you're going to become.

Is HIIT good for weight loss?

High-intensity interval training is a great form of exercise for weight loss in several different ways. HIIT can burn a high amount of calories in a short time window — with some studies even estimating up to 500 calories in a 30-minute session [9]. This means you can get more bang for your buck compared to resistance training or moderate intensity exercise.

Not only that, but HIIT can continue burn calories for hours after your session. Known as the 'HIIT afterburn', some sources estimate it increases your metabolic rate by 10% for up to 24 hours after your workout [10].

HIIT has also been found to regulate blood sugar levels more effectively than other types of exercise [11]. This is because your muscles need more energy during this type of workout, forcing blood glucose to move into your cells more efficiently. This makes HIIT particularly beneficial for those who struggle with fat loss due to insulin resistance.

Working together, all of these factors make high-intensity interval training the perfect all-rounder for weight loss. And, the research backs it up! For example, one 12-week study found HIIT participants lost an average of 5.7 kilos [12]. Another analysis reported HIIT groups showed more pronounced body fat loss than moderate-intensity continuous training groups, with one female group seeing a 26.76% decrease [13].

Is HIIT better than cardio?

Technically, HIIT is a type of cardio — it involves aerobic exercise, with the goal of getting your heart rate up. However, it's distinct from steady-state cardio, which involves a consistent, moderate-intensity pace over an extended period of time (think, jogging on a treadmill or swimming laps). So, which one is better for you? It really depends on your goals!

If your objective is fast fat loss, HIIT is going to be your best friend. That's especially true if you're time poor and find it difficult to squeeze workouts into your schedule.  High-intensity interval training can also be a great option for overall body composition improvements, because it tends to include functional compound exercises that can help preserve or increase muscle mass [14].

However, if you're new to exercise or are simply looking to shift body weight, lower intensity forms of cardio might be a better choice. Some people find that exercise styles like cycling or going to a dance class are more fun and sustainable. Plus, as they're longer, they can help you get into a mindful 'flow' state, which is highly beneficial for your mental health.

At the end of the day, all exercise is good exercise. The more you actually enjoy something, the more likely you're going to stick to it long-term. Go for what feels good for you!

How are HIIT workouts structured?

HIIT workouts typically follow a fairly predictable 'work: rest' structure. You'll perform a high-intensity round of exercise, followed by rest intervals. However, the exact ratio of the HIIT workout will depend on the style and the trainer's programming.

For example, may have a 1:2 ratio (30 seconds of work, 60 seconds of rest), a 2:1 ratio (60 seconds of work, 30 seconds of rest) or a 2:2 ratio (60 seconds of work, 60 seconds of rest). As you can imagine, the length and frequency of the rest periods can make a big difference to how challenging the workout is!

There are also a few different styles of HIIT workouts. Tabata is a common one, and involves eight intense bursts of 20-seconds, followed by 10 seconds of rest — totalling four minutes per round.  Meanwhile, in 'EMOM' or 'every minute on the minute,' you'll perform a prescribed amount of exercises and once finished, rest until the next minute starts. AMRAPs are another popular HIIT-style workout, where you'll do as many rounds as possible of an exercise within a certain time frame.

Examples of HIIT exercises

There's no one 'typical HIIT session.' The specific exercises you'll do will likely look different every time. However, typically, any exercise that gets your heart rate up quickly is popular in this training style. You'll also notice that many HIIT exercises work both the upper and lower body. Some examples might include:

• Squat jumps
• Ball slams
• Burpees
• Mountain climbers
• Star jumps
• Skipping
• Ski erg machine
• Rope slams
• Rowing
• Running
• Stair climbing
• Stationary bike
• Sled pushes/pulls
• Kettlebell swings

You might also see exercises that incorporate dumbbells and barbells ‚ but these are typically done with lighter weights and higher reps — compared to a strength training approach.

How long should a HIIT session last?

The beauty of HIIT is that it's short and sharp! The average HIIT session is usually between 20 and 45 minutes, because you don't need a lot of it for it to be effective [15]. And, when it comes to HIIT, more is not usually more. Go for any longer than about 60 minutes, and you risk putting too much stress on your body. This can be counterproductive, as it can spike your cortisol levels or increase your chances of an injury.

Who can do HIIT?

Anyone — regardless of gender, shape, size, age and fitness level — can partake in high-intensity interval training. One of the best things about HIIT is that it can easily be tailored to your goals and where you are on your fitness journey.

Who shouldn’t do HIIT?

Just because everyone can do HIIT doesn't necessarily mean everyone should do HIIT. If you have an injury or a heart condition, you'll likely want to get clearance from your doctor before you start your new exercise routine.

There is also some evidence that HIIT can increase cortisol levels [16]. So, if you are already under a high amount of stress, HIIT can potentially exacerbate the body's 'fight or flight' mechanism. This can be counterproductive, as it can put your body into survival mode, where it's more likely to cling onto visceral fat mass.

How to get started with HIIT for weight loss

While HIIT programs are designed to be fast and effective, there's no reason you can't start slow. One of the best ways you can get started with it is walking! Whether it's on a treadmill, a walking pad or out in nature, you can try power-walking for a minute or two at a time, followed by a minute of rest.

If weight loss is your goal, you'll also likely want to combine your HIIT training with intentional nutrition — and, in some cases, medical treatment. Learn more about how Juniper's program helps to unlock better weight loss outcomes through a comprehensive and scientifically-backed approach.

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