HIIT or, High Intensity Interval Training is one of the most vogue training modalities of the 21st century and now, more than ever, people are turning to it to keep them active. Indeed, it is an incredibly versatile type of training and ideal for those exercising without kit, with access only to body-weight exercises. But as with everything in life, HIIT comes with some caveats. To be effective it needs to be planned and executed in a certain way which hopefully the next few minutes of reading will help you to understand.
What is HIIT?
We'll start with the science. High Intensity Interval Training is a type of predominantly cardiovascular training, designed to maximise the total time spent between 85-95% maximum heart rate. HIIT utilises short bouts of exercise that are close to or at maximum effort (Buchheit and Laursen, 2013). These High Intensity Intervals are coupled with lower intensity (or rest) intervals, the length and number of which allow enough recovery for another high effort bout to be performed relatively soon after the previous.
So now that all the technical jabber is out of the way let me rephrase that. Essentially, if you were asked to run at a 9 out of 10 effort continuously for 2 minutes you probably wouldn’t be able to. However, if you ran at a 9 out of 10 effort for 10 seconds and then rested for 20 seconds, you might be able to complete 12 reps across a session (which equates to 2 minutes of running at a 9 out of 10 effort!). Essentially HIIT training tries to maximise the amount of very high intensity work you can fit into a short period of time.
Why use HIIT?
The real value of HIIT lies in getting fitter. One of the key factors in increasing cardiovascular fitness is maximising the time spent above 85% max heart rate (sound familiar?). This is because, the main contributor to increased cardiovascular fitness is an increase in stroke volume (the amount of blood the heart pumps out per beat; Richardson, 2000). The heart is a muscle and like every other muscle in the body the more we stress it (spend time above 85% effort) the more it will adapt (stroke volume increases) and the better our cardiovascular fitness will be (more blood pumped per beat, more oxygen to the muscles and less fatigue).
However, HIIT can also be used as a tool by coaches for body re-composition. If that term is unfamiliar to you, it simply means losing fat and gaining muscle to shift the balance between the two. Now, while HIIT is a hugely effective fat loss tool, it's influence on fat loss is more of a secondary mechanism that occurs as a side effect of its primary goal (to increase fitness). Much like how resistance training (lifting weights or training against load) is primarily programmed to build muscle or increase strength it can also have large positive effects on fat loss.
This effect on fat loss simply comes from what makes HIIT, HIIT. High intensity work. Fat loss is an energy game. If you burn more than you consume you will lose fat (Hall et al., 2012). The harder you work during exercises and the longer you sustain the work for, the more calories you burn in the session. There is also evidence that HIIT training in particular can induce a slight increase in basil metabolic rate (the amount of calories your body burns at rest) that can last for 24 hours (Petrofsky et al., 2013).
Unfortunately, the concept of HIIT has become muddled as many things are when they are thrust into the public limelight as the next saviour of exercise! More and more trainers began to construct HIIT workouts without first gaining an understanding of how and why they work. This has led to HIIT workouts with arbitrary time periods and no accurate definition of work intensity. Therefore, clients are often just completing “junk volume” that will neither make them fitter nor really aid with their weight loss goals.
So HOW do you do HIIT properly?
So if you've made it this far and you want some tips on how to effectively plan a HIIT session then you've come to the right place! Below are some of my top tips to make sure you are getting what you need out of HIIT workouts. Give them a go and watch your confidence, fitness and body composition change dramatically.
1) Stick to simple, closed chain exercises (preferably erg cardio machines) where it is easy to maintain form.
Sometimes people get carried away and want to throw over-complicated and difficult movements into the mix with HIIT workouts. While this isn't always an issue, just keep in mind the goal of the workout (to maintain >85% max HR for the specified work period). If the exercise is too complex or too hard and you burn out 10s into your 20s set, its not the right exercise for you! Some of my favourite HIIT exercises are as follows: Exercise bike, squat jumps, air squats, lunges, burpees, running and plank get ups.
2) Set a work intensity that matches the work time.
There are lots of versions of HIIT. The most widely used being tabatas (20 on 10 off etc.). Whatever work period you pick it should be matched to the intensity you complete it with. For short (<45s) work periods, your effort should be closer to maximum, while for longer (>60s) work periods, you're probably looking at between a 7-8/10 effort.
3) Match your rest periods to your work intensity.
Your body has 3 primary energy systems and all of them take different amounts of time to recover. As a rule of thumb if you're going full max out effort, you need between 1:2 or 1:5 work rest ratio (45s sprint = 4 minutes rest or 10s sprint = 20s rest). If you're below max effort you can get away with a 2:1 or 1:1 work rest period (30s work = 15s rest or 60s work = 60s rest)
4) Set rep targets to standardise intensity.
It can be really difficult to keep work intensity consistent across a set, especially as we get tired and our motivation to do so wanes. To counteract this, try and record a target to aim for on your first rep and set minimum drop off targets for each subsequent rep. For example if you're doing 15s of squat jumps at max effort, count how many you get in set 1 (lets say 12) and aim to not go below 10 until the set is over.
5) Use active rest to maximise time in high heart rate zones.
Rest periods don't have to mean fully stopping. Some research has suggested that keeping an effort of around a 4-6/10 in-between tabata style sprints (Dupont et al. 2004) can produce more favourable increases in cardiovascular fitness than simply passive rest (doing nothing). Think 15s of squat jumps followed by 15s of slow air squats as rest.
And that's it for today guys! I really hope you found value in this and it helps you all smash your home workout HIIT sessions going forward. If you did enjoy it, please share it on your pages and send it to your friends so that as many people can get the benefits from it. Alternatively, leave a like or a comment on the post letting me know what you thought (good or bad I'm always looking to learn!) or any questions you want to ask.
Tune in next week for round 3 of the blog where I'll be discussing one of my favourite approaches to hypertrophy training that is easily scaled to body-weight and limited kit. Escalating density training. See you soon!
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