Posted April 14, 2013 by Katrin Schlee in Health

HIIT – New Kid on the Block?


Have you been hit over the head with a little something called HIIT lately? If you haven’t then you are in the minority because, believe me, it is much bigger than a stone age battle club! From scientific research study to official publication to implementation by the public: we all know it takes time for any idea to filter through the layers and become standard practice, particularly when it comes to scientists trying to replace deeply entrenched and flawed beliefs with new facts. HIIT has been talked about for quite a while but has only relatively recently received the full-blown public exposure and acclaim it so rightly deserves. HIIT has been one of the most frequently used acronyms in fitness magazines up and down the country for some months and its core message is reverberating through online forums and blogs like the voice of a howler monkey echoing through the Brazilian rainforest. HIIT, or High Intensity Interval Training, is being hailed as “the new way” to exercise, drowning out all previous vociferous calls for long-duration steady state exercise and concerns over the potential for injury in high intensity training for the non-athlete.

What is HIIT?

HIIT, or High Intensity Interval Training, is – simply put – a series of intervals of low-intensity cardio alternating with bursts of high-intensity effort. The idea behind this combination is that the body has the opportunity to recover during the low-intensity part enabling you to push yourself a lot harder during the intense phase. Far from being a hyped-up exercise fad HIIT comes with a crisp white coat to back it up: scientific research has shown that post-exercise fat and calorie burning are dramatically increased. HIIT matches traditional endurance training in terms of metabolic adaptations of skeletal muscle and performance improvements, albeit at a much reduced exercise volume. So you basically spend less time working out but you do have to work much harder during that time.

So is HIIT the young kid on the block who has just arrived wearing its new Asics trainers? Or is it really the fitness veteran in disguise who has come to wrestle with a lame and puffed out gym regime? I am here to tell you that the “old school” is alive and kicking and flexing its shapely muscles. The best coaches and trainers, not to mention elite athletes, have used this method for years. Endurance athletes, too, have long used HIIT which can take up as much as 50 – 75% of their total training volume. As a core training strategy it is an indispensable instrument in the tool box of any serious coach when devising medalwinning training plans. Its main benefits? It torches body fat and elevates fitness levels in the shortest period of time. What’s not to love?

The Tabata Protocol

So how come HIIT has dropped right out of the clear blue sky and hit us like a ton of bricks without anybody seeing it coming? As a training strategy, repackaged, marketed and sold in book or DVD format, it is often and perhaps understandably advertised as ‘new’. But should we not already know about it? Let’s look at when and how it was first

In 1996 Professor Izumi Tabata of the National Institute of Fitness and Sport in Japan looked at the effects of moderate-intensity training versus high-intensity intermittent training on anaerobic capacity (the total amount of energy obtainable from the anaerobic, ‘without oxygen’, energy systems) and VO2max (the maximum capacity of an individual’s body to transport and use oxygen during incremental exercise).

Tabata’s original study used a protocol of 20 seconds of ultra-intense exercise (at an intensity of about 170% of VO2max) followed by 10 seconds of rest, repeated continuously for 4 minutes (for a total of 8 cycles). His athletes trained 4 times per week, with an additional day of steady-state training, and saw improvements similar to a group of athletes who did steady state (70% VO2max) training 5 times per week. It was established that the steady state group had a higher VO2max at the end (from 52 to 57 ml/kg/min), but Tabata’s group had started with lower levels and gained more overall (from 48 to 55 ml/kg/min). Furthermore, the Tabata athletes had gained an anaerobic capacity advantage of 28% over the steady state group. An impressive improvement!

The results of the study showed that high-intensity intermittent training did indeed improve both aerobic and anaerobic energy systems significantly, with the rate of improvement in VO2max being one of the greatest ever recorded. There is of course a strong link between improved VO2max levels and improved performance outcomes. Even though the original research was undertaken with highly trained Olympic speed skaters as test subjects training at correspondingly high levels, the conclusion was that the results could be easily transferred to sportsmen and women everywhere with a focus on accelerated rates of improvement in terms of performance and body composition. The time effectiveness of the protocol cannot be underestimated. It is worth remembering that Tabata’s athletes achieved their increases in VO2max and anaerobic capacity in one fifteenth (!) of the time it took the steady state group to achieve the same results. That’s too good to be true, isn’t it? But true it is!

How does HIIT work?

There is no specific formula to HIIT. Its effectiveness is guaranteed even in individuals who are deconditioned. Depending on your level of cardiovascular fitness, the moderate-level intensity can be as slow as walking or cycling at a moderate pace. The original Tabata protocol set a 2:1 ratio of work to recovery periods, for example, 30–40 seconds of hard sprinting alternated with 15–20 seconds of jogging or walking.

A typical HIIT session may last between ten and thirty minutes, so this kind of workout is not only effective in terms of physiological gains but also in terms of time. Individuals who are unable to spend long periods of time in the gym due to work or family commitments can no longer present any excuses as to why they are unable to get off the sofa and get fit.

What effect does HIIT have on the body?

In order to understand HIIT we need to look at the body’s energy systems. In the presence of oxygen the body will use the aerobic energy pathways; when oxygen runs out it will switch to the anaerobic pathways. The idea behind HIIT is that you work hard enough to get into the anaerobic training zone. Working exponentially harder for short periods of time means that after your exercise session the body will need to do more work to recover, a process which burns more calories. All the available blood sugar has been burnt off and so the body will need to resort to an alternative source of energy: fat. Post-exercise the body will increase its use of fat as fuel due to the fact that it has cleverly picked up on and adapted to the “stressor” of its glycogen stores being rapidly depleted during the short anaerobic bursts. In order to replenish glycogen in the liver and muscles it will have to preserve carbohydrates (so no burning there!) and will have to take its fuel from fat instead. The result is that you can sit back and enjoy your ‘free fat burning session’ whilst your body is busy making the necessary adaptations in preparation for the next assault on its glycogen reserves.

It is true to say that with Aerobic exercise you will burn most of the energy during your session. In contrast, short bursts of anaerobic exercise (HIIT) will burn a great amount of energy both during and, for a prolonged period of time, after your session. Working in the anaerobic zone helps to increase your resting metabolic rate by raising Excess Post-Exercise Oxygen Consumption (EPOC). The fat burning process after your HIIT session has ended can last for 14 hours and burn 37% more calories! Burn, baby, burn! We love it!

HIIT has been shown to reduce subcutaneous adipose tissue (fat situated directly under the skin) even more effectively than traditional much longer endurance training sessions. As explained above, the carbohydrate deficit in the body makes muscle use fat for fuel. But remember: this favourable fat-burning strategy needs to be supported by the right kind of nutritional approach in order to really come into its own. HIIT, with all its proven benefits, will still not bring about any marked changes in body composition if underpinned by a diet high in saturated fats and simple carbohydrates, no matter how hard you work. In fact, HIIT in combination with a short-term low carb diet will melt body fat even more rapidly than with a balanced intake of macro nutrients.

What about the ‘Fat Burning Zone’?

“So what about the ‘Fat Burning Zone’?” I hear you cry in astonishment. Questions such as this will naturally crop up after all the years of public indoctrination by the top health and fitness gurus. I will explain. For years Personal Trainers and other health professionals have extolled the idea of low to moderate‐intensity continuous training (LMICT), a type of training that keeps you within the ‘Fat Burning Zone’ for maximum benefits in terms of body fat reduction (as it was previously assumed). It was only just before the arrival of our ‘new kid’ HIIT on the fitness scene that the Personal Training fraternity resolved to stand united against the newly unpopular ‘Fat Burning Zone’, when, in fact, most of these Personal Trainers and of course Group Exercise Instructors had previously taught this concept for years. I remember the days when fellow trainers asked me why I was teaching classes where people had to work at such a high level. They said it really wasn’t necessary. Fortunately for my clients I have always worked this way. My core approach to teaching fitness is exactly the same as it was 10 years ago. Go hard and see results!

But let’s get back to the old FBZ. Why the sudden hate? Well, in short, staying in the ‘Fat Burning Zone’ is good — leaving it behind for much higher levels of exertion is better! I have written about longer duration exercise myself in the past as a means of effectively burning body fat. But it is not the only way. And it is not the most efficient way. It is true that if you are performing low to moderate‐intensity continuous training (LMICT), i.e. at 60 – 70% of your Maximum Heart Rate, the percentage of calories burned from fat is greater than if you were to perform a high intensity workout at 70%+ of your MHR for the same length of time. So the only real fat burning benefit arises when the low intensity workout is a long one. It is worth bearing in mind, however, that a high intensity workout will yield a greater total amount of calories burned plus it will make you burn more calories from fat after you have left the gym… in the case of HIIT the effect will last for many hours. Great news for those who would rather sit on the couch feeling like a fat incinerator than a potato.

For years I have loved the idea of weaving maximum effort phases into every one of my workouts. In all the group fitness classes I have taught over the years I have pushed my clients through cycles of hard and intense exercise interspersed with steady state aerobic work. There are no fancy explanations from me about what is happening inside the body to make clients understand complex principles: people believe in what they are doing because they see the results and those quite frankly speak for themselves. My class participants’ and Personal Training clients’ fitness levels have improved dramatically in the process, my clients’ body fat levels drop significantly with regular attendance and this fact alone is a huge motivational factor for people when making decisions about their fitness training and class attendance on a day-to-day basis.

Interestingly and contrary to popular belief, HIIT has exploded onto the health and fitness stage backed up by a significant body of research which categorically states that it is indeed a training method which is suitable and highly effective for the deconditioned, the elderly, the obese and those with cardiovascular disease. And what better reason than this for HIIT to be embraced and promoted by all fitness and health care professionals?

Look out for my next article, which will give concrete examples of HIIT routines you can try out for yourself and will also give an overview of HIIT protocols for the above groups.


Happy Training!

Katrin Schlee

Katrin Schlee
Head of BODYShoxx® Training Systems UK and Independent Health and Wellness Professional, Kat has worked in the health and fitness industry for over 10 years as a Group Fitness Instructor, Personal Trainer and Fitness Writer.