High Intensity Interval Training: How HIIT Works – SWEAT

HIIT: What It Is & How To Do It

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HIIT: What It Is & How To Do It

We get it. Finding the time to work out can be hard. If you are someone who is always on the go with work, family, or life in general, the faster you can get it done, the better. That’s where high-intensity interval training (HIIT) can help.

You might have heard the term HIIT thrown around at the gym, or amongst friends that you work out with. If you're currently on your own health and fitness journey right now, you might be wondering if a HIIT program is the best program for you.

Find out:

So, what exactly is high-intensity interval training, what are the benefits, and can it really maximise your training efficiency if you are short on time?

What is HIIT?

Designed to push you to your limits, HIIT has become a popular training choice for anyone who wants to get maximum results in little time while working towards their fitness goals.

This fast-paced training style is typically between 20-45 minutes and involves short, intense bursts of exercise. These exercises often use bodyweight, but can have added weights, like a kettlebell, dumbbell or medicine ball, and are followed by either active or complete rest. HIIT workouts will make you sweat and keep your heart rate elevated the whole time!

The idea is to work at your maximum effort. According to the American Heart Association, vigorous activity is usually around 70-85% of your maximum heart rate, which is the maximum number of times your heart will beat in a minute without you going beyond your limits.

For you to complete HIIT and get the full benefits, you need to push yourself every round!

Fast Twitch Muscle

What are the benefits of HIIT?

Are short workouts as effective as longer steady-state workouts? Here are some of the benefits of a HIIT workout.

Results continue after you complete the workout

High-intensity workouts burn more energy in a shorter period of time than steady-state cardio, generating a greater excess post-exercise oxygen consumption (EPOC), or “afterburn” effect. 

According to the American Council on Exercise, “with HIIT, you not only burn a lot of calories during the workout, but because of the high intensity you will continue to burn calories as your body replaces energy and repairs muscle proteins damaged during exercise.” You can continue to burn energy anywhere up to 48-72 hours after you finish the workout. Impressive, right?

Increases VO2max

HIIT works to improve your VO2max, which is the maximum rate at which your heart, lungs and muscles can effectively use oxygen during exercise — as stated by the University of Virginia’s School of Medicine in the US, it is considered one of the best indicators of cardiorespiratory fitness.

A 2012 study on the effect of high-intensity interval training on cardiovascular function, VO2max, and muscular force published in the Journal of Strength and Conditioning Research found that even short term bouts of HIIT (six sessions in total) dramatically improved VO2max  in a test group of both men and women.

When you have an increased VO2max, your body can gain better endurance in aerobic exercises and may also improve overall health.

Builds Type 2 fast-twitch muscle

Fast-twitch (Type 2) muscle fibres are used in explosive bursts of movements like those you find in HIIT and are important to maintain strength and a healthy metabolism. Type 2 fibres are integrated with slow-twitch (Type 1) fibres, and are found in the muscles throughout your body in different proportions — larger muscle groups like the quads, glutes and hamstrings typically contain a higher volume of Type 2 fibres.

Both your fast-twitch and slow-twitch muscle fibres interact during aerobic exercises like running, where your fast-twitch fibres are recruited first. When they begin to fatigue, your slow-twitch fibres kick into gear, and that’s when they start to take over.

As stated by the American Council on Exercise, including HIIT in your workout program can “engage more fast-twitch fibres to help you increase strength levels or become more explosive” as they require more energy to operate and grow. 

Regulates blood glucose levels

Recent studies including a 2019 article published by the American Diabetes Association suggest that people suffering from pre-diabetes or type-2 diabetes may benefit from HIIT. 

HIIT can help to regulate your appetite hormones by increasing glucose metabolism and insulin sensitivity, helping to regulate blood glucose at healthy levels. 

To ensure this training style is suitable for you, always follow the advice of your health professional. 

A more efficient form of cardio

If you’re short on time, HIIT can help you to fit a workout into a busy schedule because it is more time-efficient.


How are HIIT workouts structured?

One of the most common forms of HIIT is Tabata, which is performed for 20 “on '' 10 “off” — 20 seconds of work and 10 seconds rest. However, the recovery time can last as long as the “work” time. If not complete rest, the recovery is usually performed at 40-50% of your maximum heart rate.

Any type of cardio exercise can be done as a HIIT workout — including cycling, skipping, running or rowing. Simply set a work interval and rest period to get started. 

Sweat trainers Kayla Itsines, Chontel Duncan, Kelsey Wells and Cass Olholm include high-intensity interval training workouts in their programs, and while these workouts follow different styles of high-intensity training, they all give your whole body an intense workout!

Some of the most common high-intensity interval training styles include:


This training style involves 20 seconds of maximum effort, followed by 10 seconds of rest for a certain number of rounds. Typically, a traditional Tabata workout involves you completing eight rounds of each exercise, however, this may vary in different training programs.

Chontel includes Tabata training in her FIERCE and Full Body HIIT programs, which include six to eight exercises that you complete for two to four minutes each (six to eight laps), separated by 40-60 second rest periods.

High Intensity Strength at Home with Cass and High Intensity Strength with Cass also include Tabata workouts that train your whole body.

Trainer Samantha Ortiz-Young has collaborated with Sweat to create two fun and accessible programs Low Impact HIIT with Samantha and HIIT with Samantha which utilise Tabata-style training with different work and rest periods. 


Stands for “as many reps as possible” or “as many rounds as possible” where your aim is to repeat an exercise as many times as you can, or for as many laps of a group of exercises as you can, in a given timeframe. The goal of an effective AMRAP workout is to focus on intensity.

The following Sweat programs all utilise “as many reps as possible” as a training technique to help you build endurance.

Chontel’s FIERCE and Full Body HIIT programs include AMRAP in the high-intensity resistance sessions — think exercises like burpees, sled push and box jumps! 

Cass' High Intensity Strength programs include Express AMRAP workouts, which you can choose on the days you're short on time, and Samantha’s HIIT programs include AMRAP workouts that target your whole body.


“Every minute on the minute” — as the name suggests, the workout is broken up into one-minute intervals. During each interval, you complete a specific number of reps of a certain exercise. 

If you finish your reps before the minute ends, the remaining time is your rest. Once the minute is up, you repeat this process, start a new minute and work to complete the reps all over again.

Who Can Do HIIT

Who can do HIIT?

The great thing about HIIT is that anyone with a base level of fitness can do it. However, like with any form of exercise, there is always a risk associated with this type of training if you are a HIIT beginner or overtraining by pushing yourself too hard.

If you are new to HIIT, go at your own pace and listen to your body. If you have any prior injuries or health concerns, it is best to get cleared by a health professional before getting started.

Focus on your own capabilities — not what others around you can do — and modify where necessary. If you are completing any of the Sweat programs, you can start with the lower-intensity exercises found in the foundation weeks of each program to help you get used to the style of training. 

It’s important to make sure your exercise technique is correct, especially for fundamental movements like squats and pushups. As you become more confident, you can increase the intensity.

Examples of HIIT

Explosive bodyweight movements like tuck jumps and jump squats are examples of high-intensity exercises that can work together to form an effective HIIT workout. If you are new to this training style, try this HIIT workout for beginners.

Strength endurance exercises that include small weights, like single-arm kettlebell swings and dumbbell punches can also be used in a heart-pumping HIIT workout.

Where to perform HIIT

The great thing about HIIT is that it can be completed almost anywhere, with minimal equipment.

How To Get Started With HIIT

How to get started with HIIT

When you start something as a beginner, like a new training style, you need to take steps to ensure your success. Here are some tips for getting started with HIIT.  

Always do a warmup first

A good warmup before any workout is essential. A suitable warmup for HIIT may include low-intensity aerobic exercise like a slow jog, followed by some dynamic stretches to get your muscles warm and blood flowing.

Focus on your form

Before starting any high-intensity workout, make sure you are familiar with the exercises and confident with your form. 

If you begin to fatigue during a HIIT workout, reduce the intensity of the exercise so that you are still able to complete each rep with proper form. This might mean using a lower weight, reducing the number of reps or switching to a less complex exercise. 

A pre-workout snack might help

HIIT uses a lot of energy, so it’s important that you eat before and after your workout. Staying hydrated throughout the day and having a pre-workout meal can help you avoid feeling light-headed during your session, and having a snack afterwards can help rebuild muscle tissue.

The timing and nature of your pre-workout meal can also affect how you feel during your workout — if you eat anything too heavy or too soon before the session, you may feel uncomfortable or sick during the bouts of high-intensity exercise. 

The American Council on Exercise recommends eating a “moderate to high carbohydrate meal that [...] includes protein approximately three to four hours before the HIIT workout, and then another high-carbohydrate snack within an hour after the workout.” 

If you prefer something lighter, a banana and some nuts or a protein shake about 30 minutes before your HIIT session are other good options.

Take the time to cool down

You should always end a tough HIIT session with a cool down, using stretching and foam rolling to focus on the muscles you have just trained.


RPE stands for “rate of perceived exertion”, or how hard an exercise feels. It’s a scale of 1-10 that you can use to determine your effort during exercise. 

A score of 10 indicates a maximum effort. The work periods in a HIIT workout should be done at an RPE of 8. 

Modify to suit your ability

If you are a beginner, a good place to start is with a 1:2 ratio. For example, do an exercise for a short period of time, say 30 seconds, then rest for one minute and repeat. As your fitness improves, transition onto a 1:1 ratio.

You can also start with lower impact high-intensity exercises. For example, instead of doing jump lunges, you might start with reverse lunges, progressing to jump lunges as you get fitter and stronger.

Cool Down

How to get the most out of HIIT

Here are some workout tips to help you to get the most out of each HIIT session, and recover effectively afterwards.

Allow recovery time

High-intensity workouts like HIIT or HIRT can create elevated levels of cortisol, which is the stress hormone in your body. After a single bout of HIIT, a 2021 review and meta-analysis on the acute effect of HIIT on testosterone and cortisol levels in healthy individuals concluded that cortisol levels for almost 900 participants increased between 0-60 minutes and returned to baseline levels 24 hours after completing a workout. 

The American College of Sports Medicine recommends spreading your HIIT workouts throughout the week to allow your body to recover properly and adapt to this form of exercise, with your other workouts being steady-state workouts.

Foam rolling or active recovery may help aid muscle recovery.

Less is more

It’s important to keep your working intervals in a HIIT workout short. This will enable you to hit maximum intensity to get the full benefit of the workout with every interval. 

In the earlier week of the Sweat programs, HIIT cardio is an optional session and is only introduced as your strength and fitness increase.

Use your rest breaks

Rest breaks during a HIIT workout allow your body to work at its full capacity during high-intensity intervals. 

During high-intensity work periods, your muscles get most of their energy from the anaerobic system — the anaerobic system can provide energy quickly, however cannot sustain this energy for very long.

Your oxidative, or aerobic system, can provide energy for much longer than your anaerobic system which is why your body reverts to the aerobic system during rest, utilising oxygen to generate the energy required for your body to recover.

HIIT alternatives

Exercising at high intensity may not always be appropriate for your current health and fitness goals. However, there are plenty of other training styles that you can do to maintain and improve your fitness.

Strength training can help you to build lean muscle and reach your fitness goals, without the high impact that HIIT can have.  

Low-intensity cardio can help to improve blood circulation, reduce fatigue and place less strain on your joints, ligaments and tendons compared to HIIT.

Ramp up your next workout with HIIT

HIIT workouts have so many benefits like increasing metabolism, improving cardiovascular health, and can help to promote faster results compared to steady-state cardio. It can help you to get fitter, stronger and can help improve your overall health and wellbeing.

There are so many possibilities when it comes to HIIT, like running stairs or simply performing full-body movements such as jumping jacks — any form of exercise that can get your heart rate right up!

Have you tried a HIIT workout yet? Let us know in the comments!

* Disclaimer: This blog post is not intended to replace the advice of a medical professional. The above information should not be used to diagnose, treat, or prevent any disease or medical condition. Please consult your doctor before making any changes to your diet, sleep methods, daily activity, or fitness routine. Sweat assumes no responsibility for any personal injury or damage sustained by any recommendations, opinions, or advice given in this article.

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