What are the Benefits of HIIT Training and Workouts?
What Is HIIT | How HIIT Works | Aerobic Vs Anaerobic | Health Benefits | Pros & Cons | Is HIIT Bad | FAQs
Page last updated: 5th March 2026
HIIT training has risen in popularity over the years, becoming a firm favourite in the workout routines of everyone from beginners to fitness fanatics alike.
Alongside the many health and wellbeing benefit of HIIT training, this style of workout is highly flexible and convenient. However, there are some limitations to high intensity interval training and it's not always suitable for everyone.
Whether you're new to HIIT and looking to learn more about it, or are trying to decide if HIIT is right for you, you'll find everything you need to know about HIIT: how does it work, the benefits, and the potential downsides of HIIT too.
What does HIIT stand for and what does it mean?
HIIT stands for High Intensity Interval Training. Rather than referring to a style of exercises like strength training or cardio, the HIIT workout meaning refers to the format of a workout. The high intensity interval training definition is a workout that alternates between periods of high intensity or maximum effort exercise (around 80-95% of max heart rate) and periods of rest or recovery.
HIIT workouts are shorter, usually around 10-20 minutes and no more than 30 minutes, and the high intensity intervals are usually between 10-60 seconds. Due to the level of effort put into the workout intervals, it's unsustainable to do workouts or intervals longer than this.
There are many different styles of HIIT workout. Tabata is a popular but challenging form of HIIT which alternates between 20 seconds of intense activity and 10 seconds of rest, but there are multiple ways to format a HIIT session, for example:
30 seconds high intensity exercise, 30 seconds rest for 15 minutes
20 seconds high intensity exercise, 40 seconds low intensity exercise for 20 minutes
40 seconds high intensity exercise, 20 seconds rest for 10 minutes
Because the HIIT definition is about the workout format, you can turn almost any exercise into HIIT training. Check out some of our guides to different HIIT workouts:
How does high intensity interval training work?
HIIT is a unique style of training with unique physiological benefits, and studies suggest that just 10-20 minutes of high intensity interval training results in the same cardiovascular improvements as longer moderate cardio sessions. But exactly how does high intensity interval training work?
The short but intense exercise intervals in HIIT training quickly use up the oxygen and glycogen stored in the muscles, creating a high demand for energy. This causes several things to happen:
The afterburn effect (EPOC): The body has to work hard to replace the stored energy and oxygen, even when the workout ends. This means HIIT results in calories still being burnt for up to 24 hours after you've finished training.
Improved oxygen efficiency: More mitochondria are produced within the muscles in response to the energy demand. This improves both metabolism and oxygen efficiency, bumping up your cardiovascular fitness quickly.
Improved insulin sensitivity: HIIT improves glucose uptake and insulin sensitivity for up to three days after a workout.
Hormonal release: Intense effort exercise triggers the production of several hormones that help with fat loss and muscle repair, including human growth hormone, testosterone and adrenaline.
Aerobic and anaerobic metabolism: Alternating between high and low intensity intervals forces the body to switch between both aerobic and anaerobic pathways, getting the benefits of both types of exercise.
In simple terms, high intensity interval training works by putting maximum stress on the body, causing a series of physiological changes that result in improved fitness, high calorie burn, and preserved muscle mass.
Is HIIT aerobic or anaerobic exercise?
HIIT draws on both aerobic and anaerobic systems, which is one of the reasons it is such an effective cardio workout.
Anaerobic
During the high intensity intervals of a HIIT workout, you are working at 80-95% of your max heart rate. After 10-20 seconds, the body uses up its available energy stores and is no longer able to supply oxygen fast enough to create energy.
This causes the body to switch to the anaerobic system and break down stored glucose in the muscles for energy. This process produces lactic acid, causing breathlessness and muscle fatigue. Oxygen is required to break down this lactic acid once the workout is finished, which is what causes the afterburn effect of HIIT.
Aerobic
While the high intensity intervals use the anaerobic systems to supply energy, the recovery intervals in HIIT allow the heart rate to recover to around 70-80% of your max heart rate (heart zone 3). During these periods, the body can supply oxygen to the muscles for energy and utilise the aerobic system.
You can learn more about HIIT and heart rate zones here.
What are the health benefits of HIIT training?
HIIT is incredibly challenging, but despite this it's a firm favourite for many. This is largely in part due to the incredible health benefits associated with this style of training.
Fat burning
HIIT workouts have been shown in several studies (see examples here from 2010 and 2018) to burn more fat than traditional cardio or steady-state workouts. Using bursts of high energy movement can boost your metabolic rate and the energy burned by your body for hours, as shown in this study by the National Library of Medicine (NLM). This triggers the body to burn more fat during and, brilliantly, after you've been working out, so a 15 minute HIIT workout will keep burning calories even when you're relaxing on the sofa an hour later.
Increased VO2 max
Your VO2 max is the amount of oxygen your body is able to use during exercise (i.e. your aerobic capacity). The greater your VO2 max, the more effectively your body is able to use oxygen to generate energy and power. A higher VO2 max also helps the body to be more efficient at removing lactic acid from the blood, as your muscles get more efficient in extracting and using the oxygen. Essentially, the better your VO2 max, the better you'll be at working out and exercising. This translates across to daily activity too, so you should find walking up the stairs or running for the bus much easier.
Several studies (such as this from the National Library of Medicine) have shown HIIT to boost VO2 max and, in most cases, this happens more effectively than regular endurance or moderate level training. According to research from the Journal of Science and Medicine in Sport, if you're looking to boost your VO2 max then any kind of HIIT training will have a positive effect. However, they noted that the best kind of HIIT you can do is long-interval (so longer than two minute intervals), high-volume (a workout of longer than 15 minutes) over a moderate to long term period of time (4 - 12 weeks). That said, any form of HIIT will improve your VO2 max so if you find longer intervals of high intensity too hard right away, start with what you can manage and build your way up.
An increase in overall fitness and endurance
So as we can see from the improvements to VO2 max levels, HIIT has been proven to have a fantastic effect on aerobic capacity, but the fitness benefits don't end there. HIIT has also been proven to boost performance and endurance across the board, which means adding HIIT workouts to your routine should improve your performance in your other workouts. In one study of rowers, not only did HIIT training boost their oxygen levels, but also produced higher improvements in power output. So it made participants stronger, fitter and more effective in a shorter amount of workout time. HIIT can also help to build muscle, making it an excellent all-rounder.
Improved heart health
HIIT has been proven to reduce heart rate and blood pressure, particularly for obese or overweight people or those at risk of developing hypertension. One study showed that a group who did HIIT training three times a week for 20 minutes a day saw the same benefits to their blood pressure as a group who completed endurance training for four days a week and 30 minutes a day, despite spending half as much time exercising than the endurance training group. Other studies have also shown a huge beneficial impact to sufferers of chronic heart diseases and heart failure, thanks to the incredible benefits of improved VO2 max. Â
Great for mental health
The mental health benefits of all types of exercise are well documented. From helping to release happy hormones, improve sleep, boost confidence, build resilience and even battle depression, exercising is one of the best organic ways to improve mental health. And HIIT is no different: several studies have highlighted  a reduction in depression severity, and improvements to mental wellbeing in people who suffer with schizophrenia-spectrum disorders as a direct result of HIIT training. While the benefits are similar to those seen through other forms of exercise, the nature of HIIT workouts mean these can be enjoyed in a shorter amount of training time.
High intensity interval training: pros and cons
new) -- [summarise key advantages (time-efficient, burns calories) and disadvantages (risk of injury, not suitable for all fitness levels).]
Here are the high intensity interval training advantages and disadvantages.
The pros of HIIT
It's hard to argue with the incredible health benefits of HIIT, but there are plenty of other reasons why you might want to try this style of exercise. The overriding benefit of choosing HIIT over other styles of workouts is convenience. For example:
Time efficient
The main benefit of HIIT is that it's incredibly easy to fit an efficient and effective workout into just 15 to 20 minutes. This makes HIIT workouts much easier to slot into your day than other workouts, such as an hour of strength training or 45 minutes on the treadmill. That isn't to say those training formats don't have their own incredible benefits of course (check out why we love strength training and treadmill running here), but for those who are time poor, it is much easier to fit in a HIIT workout.
Burn more calories in a shorter amount of time
Despite working out for a much shorter amount of time, HIIT allows you to burn a higher number of calories than other types of workouts. One study compared 30 minutes of weight training, running, cycling and HIIT and discovered that HIIT burned around 25%-30% more calories. For those looking to increase their calorie expenditure and control their weight HIIT can allow you to burn more calories without spending hours at the gym, making it much easier to include in your daily routines.
Can be equipment free
Another boost to the convenience of HIIT is that you don't necessarily need any equipment to take part. While there are definitely added benefits of including weights in your workout, you can also train in one of many equipment-free styles, such as bodyweight workouts or interval running, if you are unable to access any equipment. Essentially, if you have the space, you can do HIIT, whether that's in your living room, hotel room, a park or at the gym.
Flexible formats
There are so many ways you can integrate HIIT into your workouts, which makes HIIT an accessible workout to almost everyone. Whatever style of workout you prefer, it's incredibly likely you can include high intensity training within it. Love running but are tight on time? You could try a treadmill HIIT workout and know that you're gaining fantastic results in just 15 minutes. Likewise, there are a range of fantastic options for everyone from beginners to seniors to cyclists and more - check out our The Best HIIT Workout for You guide for more.
More likely to stick to it One of the most important things when looking to improve your health and fitness is ensuring you can sustain any changes you make. Studies have found that people are more likely to enjoy and continue with a HIIT workout program, compared to continuous moderate energy training styles, likely due to the benefits mentioned above.
The cons of HIIT
With so many benefits, HIIT can sound almost too good to be true, but there are some disadvantages to HIIT too.
Risk of injury
HIIT workouts often prioritise exercises performed quickly which can make injuries more likely, as there is less attention on form and a higher chance of slipping, dropping weights, or overworking the muscles.
High impact
HIIT is often centred around high impact exercises like running and jumping, which can be unsuitable for beginners, older people, and those with joint problems. It is possible to do low impact HIIT workouts by choosing low impact but high intensity exercises, but those with joint or muscle conditions should still be cautious as performing any exercise at speed can increase risk of muscle and joint injuries.
Increase in stress levels
High intensity workouts trigger the release of the stress hormone cortisol. While this is harmless in the short term, too much HIIT and cortisol can cause inflammation and negatively impact areas like sleep, weight, and mood. Because of this, HIIT isn't suitable for doing every day and should be limited to 2-3 times a week to allow the body to rest in between.
Potential for burn out
HIIT workouts are taxing on the body and nervous system, and doing them too often can lead to overtraining, fatigue, poor recovery, changes to metabolism and poor mood. Getting enough recovery between workouts is crucial to allow the body to replenish glycogen stores, repair the microscopic damage occurred during the workout, and allow the nervous system to recover.
Not suitable for all levels
High intensity interval workouts are strenuous and significantly challenge the heart and circulatory system, and can be unsafe for people with heart problems or those who are unfit. This, along with the higher risk of injury, means HIIT workouts may not be suitable for beginners, those with certain health conditions, or some older people.
Are HIIT workouts bad for you?
Although there are disadvantages to HIIT, HIIT isn't bad. In fact, it can be a great tool for many people who want to improve their health and fitness in a short amount of time.
One of the main risks of HIIT workouts come from doing too much, without adequate recovery. High intensity exercise like HIIT needs to be balanced with plenty of rest and recovery to prevent excess cortisol levels, overtraining syndrome, fatigue, and poor mood. It's also important to focus on good form during your HIIT workout, rather than sacrificing technique for speed, to reduce the risk of injury.
For most people, limiting HIIT to just 2-3 workouts a week with at least 48h between workouts and getting good nutrition and plenty of sleep reduces the toll on your body and allows you to get the benefits of HIIT without the consequences.
However, HIIT can be unsuitable for some people due to its high intensity nature. Those with heart conditions, joint issues, injuries, elderly people, people with poor fitness levels or those who are pregnant should speak to a medical professional to understand if HIIT is right for them.
FAQs on HIIT training and workouts
How long should a HIIT workout last?
A HIIT workout should last around 10-30 minutes, but can be more or less depending on the intensity. It is possible to get a good HIIT workout in just 10 minutes!
Does high intensity interval training really work for fat loss?
High intensity interval training can help with fat loss due to the high number of calories burnt during and after a HIIT workout, which can contribute to creating a calorie deficit.
What happens to your body during HIIT?
During HIIT, your body uses up readily available energy and converts glycogen stored in the muscles into energy to be used during the high intensity intervals. During the recovery periods and after the workout, the body has to breakdown lactic acid produced from this process, which causes an afterburn effect and burns calories for up to 24h after the workout.
Is HIIT suitable for beginners or older adults?
HIIT is very strenuous and not recommended for complete beginners or older adults, unless cleared by a medical professional. However, you can build up to HIIT workouts by doing steady state cardio workouts and interval training at a moderate intensity to improve your cardio fitness. As your fitness improves, you can increase the intensity of your intervals.
Can you do HIIT every day?
No, HIIT should not be done every day. HIIT workouts are physically demanding and place stress on the body. You should have at least 48h recovery between HIIT workouts and do no more than 2-3 a week to avoid overtraining.
Who should avoid HIIT?
People with heart and cardiovascular conditions, joint conditions, injuries, as well as people who are pregnant, elderly, or completely sedentary, should avoid HIIT until cleared by a medical professional.
Is HIIT overrated?
No, HIIT isn't overrated -- it has many health benefits and is accessible for those with limited time or access to equipment. However, HIIT has limitations and should be performed no more than 2-3 times a week, alongside strength training and steady state cardio.
There are benefits to all forms of exercises; where possible, including a range of different training styles in your weekly workout routines will have the most impact on your health. Adding in a weekly HIIT session will provide a huge number of benefits to your health and wellbeing without the need to sacrifice huge amounts of time. You can also increase the challenge and the benefits from your workout by adding weights such as dumbbells, kettlebell HIIT exercises, or even barbells - learn more with our HIIT workouts with weights guide.
For more fitness inspiration, check out the Workout Exercises and Routines section of our blog. Are you ready to get started on your fitness journey? Then find a gym near you and get started today.
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