What is High-Intensity Interval Training?
A superior method of cardio for improved fitness and fat loss.
High-intensity interval training, commonly known as HIIT is a type of training characterised by short bouts of physically demanding exercise.
It’s typically done in rounds of intense work followed by slightly longer periods of recovery, repeated for a set duration. However, it can also be done using repetitions in place of time.
Examples of this might be doing 9 minutes of sprints alternating between 30 seconds of sprinting and 60 seconds of walking repeated 6 times.
Alternatively, if you were using reps and not time then it might be doing 20 burpees as fast as you can before resting for 20 seconds and then repeating this cycle for 10 total times.
These are just 2 examples of how you can HIIT training, but honestly, the options are vast. Other options include:
- Sprints
- Jump rope
- Tabata circuits
- Kettlebell swings
- Barbell complexes
It’s not uncommon for HIIT workouts to combined elements of strength, anaerobic fitness and endurance together and is often considered the most-time efficient way to train for those who want to improve fitness and lose fat fast. (1, 2)
In this article, we’ll explore HIIT training looking deeper at what it is and how to do it as well as discussing the pros and cons of this type of training.
What is HIIT Training?
To get the full benefits of HIIT training you want to be working at 90–95% of your VO2 max as this is where you’ll get the benefits of improved fitness. (3)
VO2 max is the amount of oxygen available to use for exercise, and research shows that those with a higher VO2 max lose more fat and get more out of their exercise sessions, likely because they can work harder for longer. (4)
Remember, HIIT is designed to be very physically demanding over a short period of time, which means when doing it properly you should be pushing to your max in every set.
Now, I say this knowing that unless you’re a professional athlete you probably don’t have access to the equipment you need to measure and track changes in your VO2 max.
So what do you do? Well, for us folk who are looking to get fit, look good and feel great, not perform at the highest level it makes much more sense to monitor and try to improve our work output.
This means aiming to do more work in the same amount of time in each consecutive session. Do this and you’ll still see fantastic results without needing to measure your VO2 max.
What Are the Benefits of HIIT Training?
High-intensity interval training is popular for good reason. It’s not only time-efficient in comparison to long bouts of steady-state cardio but there are also several other fantastic benefits.
Let’s take a look.
#1: HIIT Can Burn More Calories in Less Time
Perhaps one of the best things about HIIT training is that compared to other types of exercise you can burn more calories in less time, making it much more lifestyle friendly.
For example, most people will find it easier to do a quick 10–30 minute HIIT workout than they will a 45–60-minute run or walk.
When researchers compared HIIT training to weightlifting, cycling and running they found that it can burn up to 30% more calories even though they were exercising about two thirds less than the other groups. (5)
This means when done with intensity HIIT training can be done in a fraction of the time but still give you fantastic results.
#2: HIIT May Help You Burn More Fat
The way it does this is a little convoluted so bear with me.
I came across research showing this effect when looking at the impact of HIIT training on metabolism and research showing that it can increase metabolic rate through something known as EPOC or excessive post-exercise oxygen consumption. (6, 7, 8)
EPOC is essentially the additional calories you burn due to an increase in metabolism after exercise due to the increased oxygen needs of the body.
Sounds great right?! Well, it turns out that this effect is not significantly different from the increase in metabolism seen from all types of exercise.
The only difference is, HIIT results in a larger but shorter-lasting effect whilst longer duration exercise creates a smaller but longer-lasting effect. Over the course 24 hours the effects are the same.
However, an interesting point to come out of these studies is that HIIT to make the body use fat more than carbs for energy which could provide greater overall fat loss when compared to steady-state cardio. (9)
#3: HIIT Can Improve Oxygen Consumption
Oxygen consumption is related to your ability to sustain performance during exercise of both short and long durations and refers to your body’s ability to effectively use oxygen to do this.
Research how consistently shown that HIIT is just as effective at improving oxygen consumption as traditional long bouts of cardio, but does this in less time. (10, 11, 12)
I’d argue that if you’re looking to improve general fitness in the quickest way possible then HIIT is the way to go.
#4: HIIT Can Be Done Without Equipment
I’d wager a bet that along with being able to rapidly improve fitness and increase fat loss most people would also like something that is free and needs no equipment.
HIIT fits the bill on all counts here. Which means you can do it whenever you like and wherever you like without worrying about expensive gym membership or equipment.
What Are the Disadvantages of HIIT Training?
Nothing is absolute and whilst there are clearly several fantastic benefits of this type of training. In my efforts to give you a clear, rounded picture I’d amiss if I didn’t also share with you the downsides of HIIT training.
#1: It’s Not Great for Beginners
We’ve been talking a lot about how intense HIIT training is and how to get the full benefits you need to be working at your max.
Unfortunately, this means if you’re new to HIIT or exercising, it’s probably not going to be a suitable form of exercise for you.
HIIT is designed to be an intense, all-out form exercise that creates a large amount of fatigue. This means if you’re not ready you can drastically increase your recovery needs and also increase your risk of injury.
The same goes for people coming back from a long layoff or recovery from an injury too. Take the time to build up your fitness using low-intensity methods before slowly building back up to HIIT training.
Take some time to build up a base level of fitness with traditional forms of cardio or more easy-going intervals before gradually moving into HIIT training.
#2: HIIT Can Increase Your Risk of Injury
The truth is that all forms of exercise present some level of injury risk but through using proper technique and managing your fatigue and recovery you can mitigate the majority of this risk.
However, with HIIT mitigating your risk may be a bit harder than with other types of exercise. This is mostly due to how fatiguing this type of exercise and the likelihood of your technique going to shit the more fatigued you get.
This combination of fatigue and worsening technique is what’s most likely to lead to injury, especially if you’re doing circuit-based HIIT that involves a mix of exercises of varying complexity.
To help you minimise your injury risk you want to:
- Warm-up properly before working out
- Use simpler exercises that require less technical skill
- Stop or change exercises when you notice your form break down
- Build a base level of conditioning before doing HIIT training
#3: HIIT Can Impact Your Other Workouts
This is quite a specific downside and not something will impact everyone.
For example, if your goal is to improve fitness and lose some fat then doing HIIT is a perfect way to do this and provided you manage your recovery and don’t overtrain you will see results.
However, if your main goal is to maintain or build muscle and you’re only doing HIIT as complimentary cardio, then you’ll need to be mindful of how this can impact your performance in the weights room.
HIIT training is intense which means it creates a lot of fatigue and increases your recovery needs.
If you fail to take this into account by training too much, doing HIIT before you lift weights or not prioritising recovery then you’ll quickly notice your performance take a hit across the board.
How Often Should You Do HIIT Training?
This answer depends on a number of factors including your goals, training experience and current level of fitness.
This means there is no true one-size-fits-all answer.
However, I’ve found these recommendations to be suitable for most people, particularly if you have body composition goals and are also regularly strength training:
- Do 1–3 HIIT sessions a week, starting on the lower end of the scale if you’re new to it or coming back from a layoff/injury
- Always do your HIIT workout on your rest days or after you’ve lifted weights
- To keep your workouts short and intense aim to do 15–40 minutes including your warm-up and cool down
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