HIIT is a popular workout among the time poor as it promises similar results in less time.
Medically reviewed by Dr Juliet McGrattan (MBChB) and Laura Williams
Wondering if HIIT is right for you? HIIT, which stands for high-intensity interval training, is worth considering if you’re time poor and want to burn calories, reduce belly fat and boost your overall health.
With the rise of gyms like Barry’s Bootcamp and F45, HIIT training has gained popularity in recent years. Thanks to the short bursts of high intensity, HIIT offers similar (or even superior) results to other forms of exercise, including steady state cardio, in less time.
Here we look at what HIIT is, the health benefits and how to get started.
What is HIIT?
High intensity interval training (HIIT) is any exercise session where you alternate between tough, high intensity intervals of a fixed time with set rest periods. For example, you might do three rounds that include five 40 second exercises, with 20 seconds rest in between.
Intervals are usually performed at around 80 per cent to 95 per cent of your MHR (Maximum Heart Rate – the maximum number of times your heart beats in a minute). Recovery times vary and are usually taken at around 40-50 per cent MHR. Sessions typically last between 4-30 minutes.
What counts as “high-intensity” will depend on your fitness level. An elite athlete, for example, might need to do uphill sprints to elevate his or her heart rate high enough, while someone of a lower fitness level might only need to do a brisk walk or jog.
HIIT has gained popularity in recent years as a time efficient way to exercise. Not only does it offer similar results to steady-state cardio in less time, but it may also offer a range of unique health benefits.
The American College of Sports Medicine (ACSM) states that HIIT can improve cardiovascular fitness, blood pressure, insulin sensitivity and abdominal fat levels. Various studies have confirmed the positive effect HIIT has on fitness levels – great news if you’re time poor or struggle to find the motivation for longer workouts.
Here are 8 reasons HIIT is worth it:
- Burns more calories in less time
A 2015 study that measured calories burned during 30 minutes of HIIT, weight training, running and biking found HIIT burned 20 to 30 per cent more calories than the other forms of exercise.
Study participants exercised for 20 second high-intensity bursts followed by 40 seconds of rest. Meaning, they were also exercising for a third of the time as those running and biking. In effect, they were spending less time exercising while burning more calories overall.
- Reduces body fat
One study found that HIIT may decrease body fat more than other forms of steady-state cardio, such as jogging.
Researchers observed the effects of HIIT on 46 overweight men over a 12-week period. They found the HIIT group showed a significant decrease in abdominal fat compared to others.
Another study found that people who did HIIT three times per week for 20 minutes a session lost 4.4 pounds of body fat in 12 weeks without making any changes to their diet. In addition, those doing HIIT also saw a 17 per cent reduction in visceral fat during that time.
- Muscle gain
HIIT may also help with increasing muscle mass in some people.
While HIIT is unlikely to build as much muscle as weight training, it could help, particularly in those people who have previously been less active.
- Improves cardiovascular and metabolic health
A study found that HIIT improved cardio-metabolic risk factors in physically inactive adults similar to moderate intensity exercise but in half the time.
The study involved 90 adults who were previously inactive completed either a 10-week program of HIIT workouts or a traditional moderate intensity continuous training program. Those doing the HIIT program spent about 55 minutes per week exercising while participants in the MICT program spent about 128 minutes on average.
- Higher metabolism for hours after exercise
Compared to moderate exercise, HIIT seems to help you burn calories at a higher rate after you finish exercising. This is called “excess post-exercise oxygen consumption”, more commonly known as “afterburn”.
Studies have also shown that HIIT increases your metabolism after you exercise more than jogging or weight training, and may shift your body’s metabolism to burning fat for energy.
- Reduces blood sugars
Studies have shown that HIIT may reduce blood sugar, as well as improving insulin resistance more than moderate exercise.
- Improves mental health
While we already know exercise can boost mental health, studies have shown that HIIT may be especially helpful.
Another study looking at the effect of HIIT on people with chronic schizophrenia showed that people reported better mental health scores, including reduced levels of depression and social avoidance after completing the 8-week program.
In addition, HIIT may be particularly good for people with mental health issues who struggle to get motivated to exercise as it is more time-efficient.
- Time efficient
HIIT may be the ideal workout for the time-poor, as one study showed that even just 30 minutes three times a week could be enough to see the benefits.
HIIT risk factors
Despite the hype, there are also a number of downsides to high intensity training that should be considered:
Higher rate of injury
If you switch from couch potato mode to 15 minutes a day of box jumps and burpees over night, you’re asking for trouble. Many HIIT routines include high impact body weight moves – the type of dynamic, often explosive exercise required to raise your heart rate sufficiently in a HIIT routine. Start slow, don’t be afraid to sit out certain moves and remember – HIIT can happen anywhere. Cranking up the intensity on the cross trainer might be a safer way to get started.
Might not burn as many calories as you think
While the EPOC (excess post-exercise oxygen consumption) or ‘after-burn’ effect of high intensity training is not to be overlooked, beware of claims that you’ll burn hundreds of calories in such a short space of time. You can only burn so many calories in fifteen minutes and, as unpopular as this bit of science currently remains, calories count.
HIIT can be difficult to sustain
HIIT can be fairly difficult to sustain for those who struggle with motivation. Once the novelty of that initial post-workout nausea has worn off, trying to stick to a fitness diet consisting solely of higher intensity workouts may prove unappealing for some in the long term, however plausible the push from high profile fitness enthusiasts.
Who should avoid HIIT workouts?
The ACSM advise that those who have been inactive or sedentary for prolonged periods of time may be more vulnerable to the coronary disease risk with high intensity exercise, and this risk increases if any of the following are applicable:
- a family history of heart disease
- high blood pressure
- abnormal cholesterol levels
If you have any concerns about your health and ability to exercise, get the all-clear from your GP or consultant prior to going for the burn.
How to get started
Most gyms will offer some sort of HIIT classes. However, iIf you want to try HIIT out for yourself at home, the good news is that you don’t necessarily need a gym or any equipment.
Instead, focus on doing your preferred form of exercise for set intervals.
Some examples of exercises are:
- jumping jacks
- standing banded rows
- high knees
A HIIT workout might look like this:
- Warm up – 5 minutes
- HIIT circuit
- work – 15 seconds
- rest – 10 seconds
- work – 15 seconds
- rest – 20 seconds
- work – 15 seconds
- rest – 30 seconds
- work – 15 seconds
- rest – 40 seconds
- work – 15 seconds
- rest – 50 seconds
- Repeat four circuits
- Warm down stretches – 5 minutes
Tips for your HIIT workout
It’s a good idea to have a good foundation or base level of fitness before you start. Regular sessions of moderate-paced activity a few times a week (could be walking or anything that raises your heart rate) as well as some muscle-strengthening exercises is wise before starting some of the more high impact regimes .
Once you’ve got the that fitness level, follow these tips in order to get the best of HIIT:
Mix up your HIIT sessions
Most spinning and circuit classes use interval-style formats and you can do these under the eye of a qualified instructor. And low impact cardio machines such as the rower, bike and cross trainer are all good for maintaining intensity minus impact.
Strengthening your muscles with body weight moves such as lunges, squats, press ups and planks before you engage in some of the higher impact body weight exercises often favoured by HIIT routines may help to prevent injury. Burpees, and all their variations; box jumps, jump squats should ideally all be performed on relatively well conditioned muscles.
Don’t overdo the frequency
Three HIIT sessions a week should suffice, fewer if you’re starting out. Signs that you may be overdoing the tough stuff include fitness and training plateaus, feeling more tired than usual and more frequent illness.
Mix with easier workouts
Don’t neglect lower intensity workouts. You may be surprised to hear the two types of workouts tick different boxes. Low intensity exercise sessions are a great way to build a good aerobic base and burn calories without burning out.