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HIIT Workout – What It Is & Why It Works?



In 1994, Dr. Angelo Tremblay PhD (& his colleagues) from the Laval University in Quebec, Canada, performed what has become known as a landmark study in the comparison between steady state endurance training and High Intensity Interval Training.

In the study (which you can see here http://www.fastexercise.com/pdf/Canadian_Study.pdf ) subjects were divided into two groups, containing both men and women.


One group performed endurance training for 21 weeks, 4 or 5 times a week, for a total of 30-45 minutes.


The other group performed HIIT for 15 weeks, 4 or 5 times a week for 30 minutes.


The results have become legendary in the ‘fat loss world!’ The endurance group consumed almost 15,000 more calories than the HIIT group, BUT the HIIT group lost on average 9 times more subcutaneous body fat!

The question was… WHY?

Tremblay & his colleagues concluded that, “Metabolic adaptations resulting from HIIT may lead to a better lipid utilisation in the post exercise state & thus contribute to a greater energy & lipid deficit.”


What this means in plain speak is HIIT could lead to a heightened post workout metabolism that continues to burn calories for some time!

This post exercise phenomenon is known as EPOC – Excess Post-exercise Oxygen Consumption.

Now here is something very interesting for all you physics geeks (like me!) The second Law of Thermodynamics states that energy can never be created nor destroyed – it just changes form.

In the human body that means calories (potential energy) can either be stored in muscle or fat cells, or it can be converted from potential to actual energy!

Yep… The more ‘intense’ your training session the more benefit to you in your fat burning efforts. The more potential energy you will convert to actual energy & this could potentially carry on long after you have carried out the HIIT session.

This comes with a caveat of course… The more intense your training the more you have to play around with frequency and volume or over-training could be a real concern.
It also comes with a warning… HIIT isn’t for everyone & should be treated as every other training protocol; a tool to be used as and when it’s appropriate, NOT as the training protocol itself! With that said, let’s have a closer look at HIIT…


What Is Exactly High Intensity Interval Training?


HIIT is a form of exercise (any can be used) that is performed at 100% intensity for a short burst with a short recovery period & then repeated for the desired amount of rounds or time.


A classic HIIT session I use with clients is the Kettlebell Swing – Take a moderate Kettlebell (many ego lifters have found themselves staring down the toilet by not taking this advice!) and you will swing, with correct technique, as fast as you can for 30 seconds. Take 30 seconds recovery and go again. Perform for 10-20 rounds!

HIIT can also be performed as a circuit as follows. All exercises performed for 30 seconds with a 30 second rest in between each exercise:

Kettlebell Swing
Air Assault Bike
Dumbbell Squat & Press
Sprint on Treadmill

At 100 % intensity this training is brutal so please make sure you don’t a) overdo it and b) have the correct recovery protocol in place.

For the record, 100% was once described to me as imagine finding yourself on a railway track with a train baring down on you. There is a bridge 20 seconds or so ahead which you can jump safely off onto a lower track, but only if you sprint at your top speed. You make it just & bend double catching your breath for 20 seconds or so, when you happen to glance up again and see another train and so the process is repeated!

Obviously, at this level of intensity there are a few issues to be addressed…

Not everyone should be prescribed HIIT – when done correctly it is a brutal training tool… As such there needs to be a good level of fitness and health in the person attempting it.

You need to be able to recover… HIIT can (& often does) leave your central nervous system & immune system compromised for some time, so it’s not an everyday training programme.

Understand that if you choose to train this way often then you must realise the relationship between frequency, intensity, & volume… In a nutshell, the more you use HIIT the less intense each session needs to be and the less volume you can do safely!

What this means is it’s not really HIIT!

Train safe, train smart, leave the ego at the door, & use HIIT briefly for full benefit!


HITT is extremely popular, and for good reason!



Paul Webb

Ex Athlete & Strength Coach


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