I thought the best way to begin this book would be to motivate you by highlighting the large gap in potential achievements when comparing HIIT to CT, taking into account a range of common exercise aims. As you’ll see, HIIT is superior to CT in every way.
We’ll now compare the two training methods in the following areas:
Exercise Enjoyment Weight Loss Exercise Duration
Improved Fat Burning Capacity Anaerobic Threshold
Maximal Oxygen Uptake / VO2 Max Athletic Performance
When most people begin an exercise regime, they assume that CT is the only form of aerobic exercise there is, even though there are many things you can do with CT; treadmills, cycling, rowing, skipping, stair climbing, elliptical trainers etc.
Due to the usual fitness advice that new exercisers receive, they envisage many hours toiling away while staring at a blank wall.
For most people, CT soon gets boring. Exercising at the same, or very similar levels for 45+ minutes can be rather monotonous for the vast majority of people.
Surveys repeatedly show that boredom with exercise is one of the main reasons people give up. I’m sure you can relate to this.
What can be more boring than sitting on a stationery exercise bike (or insert machine here) for 45 minutes, peddling away at the same speed and intensity for the entire duration?
With HIIT, because you are constantly changing the pace, it’s far more interesting. Informal discussions with clients show that rather than dreading the thought of an exercise session, they actually look forward to the thought of a HIIT session and all it involves.
There’s something extremely enjoyable about running on full burners for only a few seconds before having a nice gentle stroll, then going full throttle again.
A problem with CT is that the thought of only being ten minutes into your run and having another 30+ minutes remaining and at the same pace can be rather demotivating.
However with HIIT, knowing that you’re running at an intense pace for only a few more seconds before having a nice easy walk for one or two minutes for example can be pleasing to the mind and can spur you on indefinitely.
Working at high intensities is a lot easier if you know you have a rest coming up round the next corner.
This can be backed up by taking a look at a study carried out at Liverpool John Moores University in 2011. The aim was to compare ratings of perceived enjoyment between one group partaking in HIIT and another in CT.
The first group of 8 men performed 6 high intensity intervals running for 30 seconds at 90% of their maximal heart rate. These intervals were interspersed with 3 minute periods of walking at an easy pace.
The second group ran for 50 minutes at a constant pace equivalent to 70% of their maximal heart rate. All participants assessed their enjoyment by using the Physical Activity Enjoyment Scale.
This scale consists of 18 questions where subjects rate their enjoyment on a scale of 1 – 7. The higher the scores – the greater the enjoyment.
Ratings of perceived enjoyment in the HIIT group were rated at 88 points whereas the CT group rated their enjoyment at 61 points. This was despite ratings of perceived exertion actually being marginally higher within the CT group.
But for those reading this book who regularly participate in HIIT and for those who are about to find out for the first time – The fact that HIIT is more enjoyable than continuous training should come as no surprise.
Studies have indeed shown that when it comes to weight loss, HIIT is far superior to CT.
In 2011 at the University of Western Ontario, 20 men and women were assigned randomly to a HIIT group or a CT group.
In the HIIT group, subjects were required to run on a treadmill with 4 to 6 bouts of all out sprints lasting 30 seconds.
Each 30 second bout of all out sprinting was separated with recovery periods lasting 4 minutes. The CT group jogged on a treadmill at around 65% of their maximal heart rate for between 30 and 60 minutes.
Training sessions for both groups took place 3 times per week for a duration of 6 weeks.
What were the results? After the 6 week study, subjects in the CT group lost a total of 5.8% of their fat mass. This is great news.
But what about the HIIT group? Subjects in the HIIT group lost a total of 12.4% of their fat mass.
The results speak for themselves that HIIT is clearly superior over CT when it comes to fat or weight loss – At least this is true when participating in HIIT sessions 3 times a week over a 6 week period as in the study.
But does partaking in high intensity activities provide superior results when they are carried out habitually over a longer period of time? Let’s take a look at another study.
In 1990, The American Journal of Clinical Nutrition analysed data taken from the Canada Fitness Survey. In the survey, 1366 men and 1257 women aged between 20 – 49 were analysed for body fatness, fat distribution (waist to hip ratio measurements) and energy expenditure, frequency, intensity and duration of habitual leisure time activities.
All data was collected via use of an extensive questionnaire as well as by physiological measurements taken in a clinical setting.
In order to determine the effect of exercise intensity on body fatness, subjects from each sex were divided into four sub-groups taking into account the metabolic equivalent of task (METS) value of their leisure time activities; Group A – subjects not reporting activities of 5 METS, group B – between 5 – 7 METS, group C – between 7 – 9 METS, group D – subjects reporting activities of 9 METS or higher.
Before I give you the results, let’s take a look at a few examples of METS values.
Sleeping scores a METS value of 0.9, walking at 3 mph (4.8 km/h) gives a value of 3.3 METS, whereas for HIIT purposes, sprinting or rope jumping would give a METS value of 10.
Every single activity in existence has been given a METS value, which effectively grades the physical intensity of the given activity.
If you’re curious about how intense your job or favourite hobbies are considered then simply carry out a web search for the Compendium of Physical Activities.
The results of the study showed that group D had the lowest waist to hip ratio, lowest waist circumferences and lowest body fat percentages over all other groups and in both sexes.
This held true despite group D actually expending a similar amount of total energy during activities as did group A but much less than participants in groups B and C.
Let’s clarify here that in the study, participants in group D expended similar amounts of energy during activities as did group A (but less than groups B and C), yet their body compositions were completely different.
Clearly there are other factors coming into play here and of course we’ll be discussing them shortly.
So why is HIIT so superior for weight loss over CT? Well there are two main mechanisms for this.
It has long been known in physiology that when you increase the intensity of the exercise; you actually increase the rate of carbohydrate metabolism and therefore decrease the rate of fat metabolism.
You’re probably thinking that if you want to lose weight, or more specifically you would like to lose fat then this would run counter to achieving your aims.
However, when you increase the exercise intensity, you also increase the total caloric expenditure, in fact the total caloric expenditure increases exponentially.
So if you burn a greater percentage of fat calories from lower intensity exercise, the total number of fat calories actually burned off is far lower due to the lower total amount of calories actually used in the activity.
Whereas if you increase the intensity; you’ll burn off a lower percentage of fat calories but from a far higher total caloric expenditure.
If you think about the logic behind this; a lower percentage of a greater number is far more than a higher percentage of a much lower number.
Unfortunately there remains many health care professionals that don’t quite understand this logic and so their patients and clients never experience the benefits that come from higher intensity activities.
It is understandable to assume that by engaging in lower intensity exercise, patients would be oxidising a higher proportion of fat to carbohydrate than by engaging in higher intensity activities and so this approach would appear superior for weight loss.
By considering the energy spent during exercise, this hypothesis seems to be justified on some levels.
However, as we are beginning to learn, this simply is not true. Clearly there are other factors working here, such as what happens post exercise.
It’s these post exercise mechanisms that are too often overlooked, even by health care professionals and many personal trainers, especially when it comes to cardiovascular training.
The other mechanism is excess post exercise oxygen consumption (EPOC). Please read the section entitled Improved Fat Burning Capacity below as we’ll be discussing EPOC in great detail there.
And another thing – Take another look at the study above. There’s one thing in that study that the sharp eyed reader will have noticed. This brings us to our next sub-heading.
Look again at the duration of exercise in the two subject groups above. What do you spot?
When reading this study, you’d think there was some kind of a mistake. In fact for the study to have been fair, both groups really should have had similar exercise durations but this wasn’t the case.
In the study, the CT group exercised for an average of 45 minutes per session.
Compare and contrast that to the HIIT group that exercised only for an average time of 22.5 minutes per session.
You read that correctly; the HIIT group exercised for precisely half the time of the CT group.
Yet by the end of the study and the subjects all had their body fat percentages taken again, the HIIT group had lost more than double the fat that the CT group had lost; 5.8% in the CT group and 12.4% in the HIIT group.
The study shows without doubt that you can lose more than twice the amount of body fat by performing half the amount of exercise with HIIT over CT.
In practical terms, this means you can shorten your HIIT session considerably and still attain superior benefits over and above a much longer and less interesting CT session.
Are you beginning to see the benefits of HIIT now?
In fact, what is the number one reason why most people claim not to take part in any fitness activities?
It’s not out of laziness or lack of money, but instead lack of time is cited. By making proper use of HIIT, you can attain superior benefits over CT with only a fraction of the time being invested.
So we’ve established that your HIIT sessions really don’t need to be that long in order to achieve incredible and even superior benefits over CT.
But how much time during the actual week must you put in? How many individual exercise sessions should you take part in to see these benefits?
Well in the study above, a 12.4% reduction in fat mass was achieved in just three individual sessions per week (for 6 weeks). I’m sure I don’t need to tell you just how incredible this is.
However, I can refer you to one study that tested the results of only a single bout of HIIT per week on cardiovascular mortality; cardiovascular disease being the single largest cause of death throughout the entire world.
This study was truly huge, monitoring 56,000 men and women over a 16 year period.
The results were that for cardiovascular disease prevention, a single weekly HIIT session significantly reduced the risk of death in both men and women.
Interestingly, they discovered that increasing either the duration of a single HIIT session or the frequency of weekly HIIT sessions had no additional benefits when it came to prevention of death from cardiovascular disease.
This study goes to show that if your goals are not weight loss, but more fitness maintenance and disease prevention, all you really need is a single 22.5 minute session per week in order to achieve this.
In reality, who can now cite lack of time as an excuse for not exercising?
Improved Fat Burning Capacity
It is known that the more you exercise the greater fat burning potential your body creates for itself.
What I mean by this is that the more you exercise, over time your body becomes more efficient at burning fat no matter if you’re out and about engaging in your daily business or even when you’re sat on the couch watching a movie.
Why is this? There are several mechanisms within the body that makes this the case.
Increase in Mitochondria
The first of those mechanisms is the increase in the number of and the size of the existing mitochondria within the muscle cells.
Mitochondria are known as the cells “power houses” as this is where glycogen is oxidised and energy is created. When we exercise, over time the increase in mitochondria and their efficiency enhances the body’s ability to burn fat for us.
So how does this increased capacity compare between HIIT and CT? Let’s have a look at another study.
At the University of Guelph, Ontario in 2008 the study was intended to observe HIIT and its ability to improve the body’s fat and carbohydrate metabolic capacities in untrained individuals.
The subjects took part in 10 x 4 minute bouts of high intensity cycling separated by 2 minute recovery periods. Exercise sessions took place 3 days a week for a duration of 6 weeks.
At the end of the study, a resting muscle biopsy was taken and there were found to be increases in citrate synthase (26%), a mitochondrial enzyme and 2 different fat transport proteins (14% & 30%).
It was found that while cycling at a steady pace of 60% of their maximal heart rate potential, there was a marked increase in fat and carbohydrate oxidation capabilities.
Unfortunately, one limitation of the study was that it did not compare HIIT subjects with CT subjects which would have been interesting to observe.
Just to clarify, the study showed that the marked increase in fat and carbohydrate oxidation capabilities were for CT workouts after the HIIT sessions.
This shows that after performing HIIT for a period of time and then returning to CT, your body has become more efficient at burning fat.
In another study at the same university in 2006  8 women took part in 10 x 4 bouts of high intensity cycling with two minute recovery periods.
The subjects took part in 7 exercise sessions over a two week period. At the end of the study, fat oxidation capabilities had increased by 36%.
Yet again unfortunately, there was no CT group to compare results to. You’d hope they would have learned their lessons at this university but the good thing that came out of the study was that you can see incredible increases in fat burning potential after only 7 exercise sessions. This is the power of HIIT.
However I will now bring your attention to another study that took place at McMaster University in Ontario in 2006. I’m assuming there must be some kind of rivalry between the Ontario institutions to become the authority in HIIT research.
16 men were randomly assigned to either a HIIT group or a CT group.
Each group performed 6 training sessions over 14 days on a bike.
The HIIT group took part in 4 – 6 x 30 second all out bouts of exercise with 4 minute recovery periods between.
The CT group took part in 90 – 120 minute bouts at around 65% of their maximal heart rate.
The muscle biopsy samples taken before and after the study showed that there were similar increases in fat and carbohydrate oxidative capacity in both groups.
But yet again – what stands out from the study above?
Take another look at the overall exercise durations for both groups because the differences here are massive indeed.
The HIIT groups exercise sessions lasted for an average of 22.5 minutes compared to the CT group which lasted for 105 minutes.
Over the duration of the study this works out at 2 hours 15 minutes (HIIT) and 10 hours 30 minutes (CT).
There you have it. With only a fraction of the exercise duration, HIIT is comparable to CT when it comes to increasing muscle fat and carbohydrate oxidative capacity.
Excess Post Exercise Oxygen Consumption (EPOC)
The second mechanism I referred to is termed oxygen debt or excess post exercise oxygen consumption (EPOC).
If you read a lot on the subject of health and fitness then you may commonly hear EPOC described as the after burn effect.
When you exercise on full burners as you would with a HIIT session, the aerobic system alone cannot possibly supply you with enough energy to fuel the activity.
Although it will do its best and give you all it has, the anaerobic system will have no choice but to come into play to provide extra energy assistance.
This point typically comes in at between 65 – 85% of your maximal heart rate, as we’ll discuss in the next section.
I will explain the principle of EPOC with the help of an example.
Imagine you were going for a swim from one side of a lake to the other.
You knew it would take an hour to complete this swim so naturally, you decide to pace yourself.
Even if it was your goal to reach the other side of the lake in as fast a time as possible, you would still pace yourself so you wouldn’t run out of energy too soon.
But what if a shark suddenly appeared and started to swim towards you?
Luckily you see a large rock directly in front, about a minutes swim away; so you turn on the full throttle and give it everything you have to reach the rock in order to save your life.
Now, would you say you would be breathing harder after reaching the rock or after reaching the other side of the lake? Of course the answer is that you’d be breathing harder after reaching the rock.
This is because turning on full burners has placed immediate and great stress on your aerobic metabolism; this is partly why you’re breathing so hard.
A very basic evolutionary and physiological principle is that your body adapts to stress.
So if you escape from sharks on a regular basis, or better yet, mimic the shark part in a more controlled environment such as a swimming pool then your body is going to change for the better.
Another reason why you are now breathing harder after reaching the rock than when you reach the end of the lake is because you are now requiring additional oxygen to replenish significant energy stores that were used in haste via non-oxidative metabolic pathways in order to save you from the shark.
Now this part is very important; you will now need to deal with the incredibly large amounts of lactic acid that have built up in your muscles during the swim as a result of turning on the full throttle.
The build-up of lactic acid has had nothing to do with the duration of the swim at all, but is there solely due to the high intensity of the swimming, having escaped from the shark.
This elevated level of oxygen consumption, which will last for several hours, will continue to have a training effect on the body. This is what is meant by the term EPOC or the after burn effect.
You have finished training, yet you are still burning fuel or calories at an elevated rate due to the high intensity of the activity.
Let me reiterate that there is no EPOC from CT because the activity is just not intensive enough.
EPOC is only gained after high intensity activity.
How long will EPOC last for? That all depends on exactly how intense the activity was.
The more intense the activity – The greater the EPOC.
Naturally, the effect of EPOC is at its maximum during the first few hours post exercise when the body has the greatest need to recover.
The effect of EPOC then gradually diminishes over and up to the next 48 hours – The harder the intensity of the prior activity, the longer EPOC lasts.
Are you now imagining the physiological benefits that are possible by engaging in regular and sustained HIIT? The potential is massive.
So why else are there such incredible differences in improvements between HIIT and CT?
Well this has to do with the body’s energy systems. There are three energy systems in total; the ATP system, the glycogen or lactic acid system, finally there is the aerobic system.
Each system uses fat and carbohydrate for fuel in different frequencies.
Each system is used in different proportions depending on the exercise intensity. They are working all the time in the background and slide in and out of action depending on what we’re doing.
The ATP system is used for high intensity work such as sprinting and lasts usually for 10 seconds or less before becoming depleted.
The term ATP refers to adenosine triphosphate which is in rare supply in the body, but don’t worry, once it runs out the body can quickly make it again, luckily for those who do HIIT regularly.
The glycogen/lactic acid system lasts for a bit longer, usually for between 30 seconds to up to 3 minutes and beyond depending on your fitness.
Glycogen is the body’s supply of fuel which it uses for everything; it tends to be made available to order.
The aerobic system is the system we use the vast majority of the time; when we’re eating, sleeping, watching TV or performing very light to moderate exercise.
When we perform CT for long periods, we are only in effect using the one energy system; the aerobic system.
It’s only when we cross the 65 – 85+% of our maximal heart rate threshold (depending on how fit you are) does the glycogen system come into play. This is where we are in effect utilizing energy on two levels.
This is the spot we must aim to hit (or even higher), albeit for only a short duration when partaking in HIIT.
In fact, in HIIT we should aim to go for 100% of our maximal heart rate in order to train our ATP system also. This way we’re utilizing energy on three levels, not two and not one.
Unlike CT, HIIT gives a workout to all three energy systems and not just the aerobic system.
This gives us an all-round better workout and has many physical benefits for us that a less interesting CT session can’t touch.
By participating in HIIT, you receive a large increase in post exercise fat burning over and above what CT can do. You should think of this as free training time because you have ended your workout session, but your body is still burning fat at an elevated rate.
To clarify this point a little more, I’ll reference a study that showed that 24 hours after a HIIT session, HIIT subjects were still burning calories at an elevated rate, whereas the CT subjects were not.
Over the 24 hour period that followed HIIT sessions, this equated to an extra 100 calories burned over the CT group.
This is quite significant and why HIIT participants can burn more energy and lose more fat by carrying out a lot less work than CT participants.
To really hammer home the fact that you continue to burn fat at an extremely elevated rate following HIIT workouts, I will reference another study that took place at Laval University in Quebec in 1994.
The study was designed to discover the outcome of CT and HIIT on body fatness and muscle metabolism.
32 men and women were assigned randomly to a CT group or a HIIT group. The CT group took part in a 20 week programme whereas the HIIT group took part in a 15 week programme. By the end of the protocol, the mean estimated energy cost of the CT group was 120.4 MJ and the mean estimated energy cost of the HIIT group was 57.9 MJ.
Now consider that these figures represent the energy cost from the exercise activities only and not with the inclusion of EPOC.
Consider also that the CT group’s exercise programme lasted for a full 5 weeks longer than that of the HIIT group. This isn’t how I would have designed the study, but let’s run with this.
At the end of the study, body fat skin fold measurements were taken and the HIIT group were found to have undergone a reduction in body fat a full nine times greater than that of the CT group.
Read that again. Nine times greater!
All this despite the amount of energy actually used during the exercise activities were more than two times greater in the CT group over the HIIT group.
Clearly the only way this can be explained is that there are energy sapping physiological changes taking place only following exercise that produces high quantities of lactic acid (HIIT).
It further goes to prove that it’s not about the duration of exercise, but the intensity.
I’m sure you’ve heard of the old saying “no pain – no gain” which was coined by Benjamin Franklin.
It appears it really is the truth.
What does the anaerobic threshold refer to? It refers to that moment when you cross over from the aerobic system to the glycogen/lactic acid system.
When exercising at any given intensity, lactic acid builds up in the bloodstream.
The higher the intensity, the faster it builds up. When exercise intensity increases to an extent where the production of lactic acid is in excess of its rate of removal/metabolism in the blood then it inevitably builds up to a more noticeable concentration where we begin to feel pain.
This is termed the anaerobic threshold.
In real terms, when exercising it’s that moment when the painful, performance inhibiting build-up of lactic acid can be felt in the muscles.
Typically, in untrained individuals, the anaerobic threshold will arrive at around 65% of the maximal heart rate.
The fitter the individual is, the higher the anaerobic threshold.
Therefore if we only carry out CT work then we will seldom cross over the anaerobic threshold.
What problems does this bring? Well it means you’ll not be training your other energy systems.
When we cross over the anaerobic threshold repeatedly such as during HIIT, we’re in fact regularly training the anaerobic energy systems (glycogen/lactic acid system and the ATP system). So what effect will this have on us?
Because we are creating more lactic acid within our muscles, our bodies will have to adapt to this. Over a short space of time our anaerobic threshold will be pushed back.
So instead of feeling that painful lactic acid build up at 65% of your maximal heart rate, you’ll now be feeling it at 70% of your maximum, and then 75%, then 80%.
What is happening is that your body is becoming much more efficient at dealing with the painful lactic acid build up, enabling you to work harder and for longer without feeling that burn.
If you push back your anaerobic threshold then by definition, you are increasing your aerobic capacity because the amount of work you can do aerobically has increased in proportion to anaerobic work. In real terms, what effect does this have on your life and functionality?
Well having an increased aerobic capacity can improve your life in many ways, particularly if you were previously deconditioned.
No longer will you be exhausted simply by going about your daily routine.
No longer will you feel a build-up of lactic acid from taking part in any previously painful physical activity.
Can you see how this can improve the quality of life for unfit individuals?
You’ll be able to go on walks in the countryside, on vacation and play with the kids and not have to break a sweat.
If shopping for groceries for example was previously strenuous for you, you should now be able to handle this chore without the feeling of exhaustion you had before.
This is one of the positive training effects of HIIT. We are becoming fitter in ways that CT can’t reach.
HIIT increases our tolerance to ever more intensive exercise. This is why professional athletes such as Footballers will often train using HIIT since it helps delay the build-up of lactic acid and therefore fatigue.
This has obvious benefits for those partaking in sports where there is constant stopping and starting action such as Football, Rugby, Badminton, Tennis, or pretty much the vast majority of sports in existence.
Let’s compare the effects of CT and HIIT on anaerobic threshold by taking a look at a study published in the American Journal of Cardiology in 2005.
The study subjects were 14 men who had recently undergone heart bypass surgery. The subjects were split into a CT group and a HIIT group.
The CT group took part in a 10 minute warm up, 30 minutes of training at 65% maximal heart rate followed by a 10 minute cool down.
The HIIT group took part in identical warm ups and cool downs. Their training protocol was 2 minutes training at 90% maximal heart rate with 2 minute recovery periods at 40% maximal heart rate.
The total exercise duration was 30 minutes, the same as the CT group.
The length of the study was 16 weeks and subjects trained two days a week.
All subjects rotated training equipment; treadmill, stair climber and a combined leg and arm cycle ergometer to add variation.
Due to the length of the study and to keep everything fair as well as practical, as fitness levels increased, the individual intensity was increased on a daily basis.
Anaerobic threshold was measured by “time to exhaustion” in seconds while working at 90% maximal heart rate. Both groups were measured at the beginning and end of the study.
At the beginning, both groups measured an average time of 100 seconds to exhaustion.
At the conclusion of the study, the CT group measured a much improved time of 230 seconds to exhaustion.
However, the HIIT group measured a far superior time of 480 seconds to exhaustion.
To conclude; anaerobic threshold was significantly increased in both groups, but to a far greater extent in the HIIT group.
The study showed that HIIT is far superior over CT in giving us a greater tolerance to an aerobic challenge.
The study also showed that high intensity training can be safely carried out by an “at risk” group such as those recovering from heart bypass surgery.
By increasing tolerance to hard work to such an extent as this, it should be easy to realise the benefits this would have for the individual concerned.
Gone will be the days when thieves could snatch your wallet and expect to make a clean getaway.
While anaerobic threshold refers to the intensity of work possible before reaching the glycogen/lactic acid system, anaerobic capacity refers to the amount of work that can be carried out using both the glycogen/lactic acid and ATP systems.
It’s the capacity of work that can be carried out between first feeling pain and quitting altogether in a heap on the floor.
I will now demonstrate how compact it’s possible to design your workouts while still achieving superior gains by referencing an extremely famous study by a Japanese scientist whose name you may well recognise.
In 1996, Dr Izumi Tabata designed a study with the aim of discovering the effects of CT and HIIT (actually Tabata) on anaerobic capacity.
Using a cycle ergometer, subjects exercised 5 days per week for 6 weeks.
The CT group worked for 60 minutes at an intensity of 70% maximal heart rate.
The HIIT group worked for 20 seconds at 100% maximal intensity with 10 seconds rest for a total of 8 bouts.
The total time for the HIIT workout was – only 4 minutes.
At the end of the study, the CT group were found not to have undergone any significant increases in anaerobic capacity.
This is not really surprising considering subjects exercising at a steady state of 70% maximal heart rate would have been unlikely to have passed the anaerobic threshold.
The HIIT group however had experienced gains of 28% in anaerobic capacity. All this from exercise sessions consisting of only 4 minutes.
Now, to many reading this book, you may be thinking – well that’s all well and good, but when will I ever need to exercise until I drop? To which I would say – hopefully you’ll never have an emergency where you’ll need to sprint like your life, or the life of a loved one depended on it.
But having an increase in anaerobic capacity should be considered a bonus for any professional or recreational sportsman who regularly delves past the anaerobic threshold.
Just like HIIT itself – Tabata, which is a form of HIIT is becoming increasingly popular the world over. We will revisit Tabata in the HIIT Protocols section.
Beta-endorphin is the “feel good” molecule that is responsible for how we often feel euphoric following an extra strenuous workout.
It’s formed in the hypothalamus of the brain as a response to pain. When we feel pain, either emotional or physical, it’s soon numbed due to the release of beta-endorphin.
Other functions of beta-endorphin as well as pain relief and giving us the feeling of euphoria is that it’s known to slow the growth of cancer cells and it can help us relax too.
Since beta-endorphin is formed when we experience pain stimuli, we know that large amounts are synthesized when we perform strenuous activity such as HIIT.
This is in response to the painful feeling of lactic acid that builds up in our muscles; the beta-endorphin tries to dull that pain.
Therefore when we only perform CT workouts, beta-endorphin is not created to the same extent.
In fact: “Published studies reveal that incremental graded and short term anaerobic exercise lead to an increase in beta-endorphin levels, the extent correlating with the lactate concentration.”
Of course, by “anaerobic” it means a more intense workout such as HIIT. The study showed that a greater amount of beta-endorphin is produced the harder you work out since you’ll be creating more lactic acid and the beta-endorphin is created as a response to that.
The study also went on to confirm that beta-endorphin levels do not increase with exercise performed at a steady state, such as with CT unless the CT lasts for longer than one hour.
This would explain the “runners high” phenomenon which is often reported by long distance runners.
The whole point of this section is to demonstrate how the “feel good” chemical which affects our moods is more easily created from a HIIT workout over a CT workout and that by training in intervals at high intensity you are setting yourself up for a day in a euphoric state.
It has long been known that exercise triggers positive feelings, makes us feel invigorated and is also a great treatment for depression, however the correlation between intensity of the exercise and feelings has not always been known.
Maximal Oxygen Uptake / VO2 Max
It is a person’s VO2 max which is often used to derive their overall fitness.
According to the American College of Sports Medicine (ACSM), cardio-respiratory fitness is determined by oxygen consumption, technically termed VO2.
The “V” stands for Volume, whereas the “O2” obviously means Oxygen. It’s measured as a relative rate in millilitres of oxygen per kilogram of bodyweight per minute (ml/kg/min).
VO2 max refers to a person’s overall capacity to transport and use oxygen during exercise.
As we exercise more and more, this capacity improves as our lungs and heart become more efficient at pumping oxygen rich blood around our bodies to the muscles which in turn become more efficient at using it.
So let’s take a look at a couple of studies which compare and contrast HIIT and CT with regards to VO2 max.
In one study, 27 heart failure patients with a mean age of 75 were split into HIIT and CT groups.
The HIIT group exercised at a rate of 95% of their maximal heart rate.
The CT group exercised at 70%. Sessions took place 3 times a week for 12 weeks and VO2 max was measured both before and at the end of the study.
After 12 weeks the HIIT group increased their VO2 max by 46% whereas the CT group increased theirs only by 14%. This is great news for HIIT.
In another study, 25 boys with a mean age of 10 were assigned to either a HIIT group or a CT group.
The CT group cycled for 20 minutes per session at 80 – 85% of their maximal heart rate.
The HIIT group carried out 30 second sprints on a stationery cycle interspersed by recovery periods for a duration of 20 minutes. VO2 max was measured at the beginning and end of the 8 week study.
At the end of the study, both groups showed increases in VO2 max, with the HIIT group being the clear winner.
There you have it.
When it comes to improving your overall fitness, as measured by VO2 max, which is as good an indicator of overall fitness that has ever been developed, HIIT is clearly superior to CT.
But what else did you notice about the two studies above?
Well the first study was carried out with heart failure patients, the oldest of whom was 86 years old.
In the second study the subjects were young children. Both studies involved strenuous exercise at 95+% of their maximal heart capability.
These studies together go to show that HIIT, despite being highly vigorous is indeed safe and even encouraged for absolutely anybody, no matter what their age or physical fitness.
Have you ever considered being tested for your own VO2 max?
There are several ways of going about it.
Perhaps the easiest method involves the treadmill or stationery bike at your gym (if you’re a member of one).
Typically you’ll warm up for a few minutes then you will run, walk or cycle with increasing speeds, gradients or resistance until you can no longer perform.
Since the aim is to discover the maximum quantity of oxygen your body is capable of taking in, you’ll be sent to your limit (be warned) and at this point, the time you lasted until is recorded.
This time is then placed into an equation, taking your gender into consideration (as well as age and other factors depending on the equation used).
You will be given a final number which is your VO2 max in millilitres of oxygen per kilogram of bodyweight per minute (ml/kg/min).
With this number you can of course compare it to the norms for your age and gender if you choose to.
But more importantly, you should keep a note of your score and use it as a benchmark for VO2 max tests in the future.
I can assure you that by taking regular HIIT sessions, your VO2 max will increase at a promising rate.
Which sports actually involve long periods of continuous activity? There are a few but really not that many; distance running, distance swimming, distance cycling and distance rowing etc.
When you think about it, nearly all sports involve some kind of stopping and starting action.
From combat sports like boxing and martial arts, racket sports such as tennis and squash, all the way to team sports such as football, both American and soccer as well as basketball or ice hockey.
Also there are track and field sports such as jumping, both long and high, shot putting or any throwing event and naturally there is sprinting too; all these sports as a consequence of short bursts of high intensity action will involve the rapid build-up of lactic acid.
Therefore dealing with this painful performance crippling lactic acid is of paramount importance to all athletes or even to the recreational sportsman.
If you are unable to deal with high lactate concentrations then you will be at a major disadvantage when compared to any opposition who is HIIT trained.
And not just your opposition either – But you will also be up against anybody vying for that same position as you on the sports team, for example, your teammates.
As with anything in life, if you want to get good at something then you need to practice it.
So if in your sport there is a need to deal with high concentrations of lactic acid, then in order for your body to get good at removing it, you’re first going to need to produce a lot of it.
Your body will soon find the best way of dealing with the lactic acid and you will adapt as a consequence.
By now you should be well aware that HIIT is the single most effective method of creating this lactic acid build-up.
By now you may not be surprised to know that the improved ability to deal with lactic acid build- ups can come extremely quickly by partaking in HIIT.
One study has shown that only six sessions of HIIT over a two week period can significantly reduce the build-up of lactic acid in the legs following high intensity cycling.
Having a superior ability to deal with lactic acid build-ups in your body will give you a significant advantage over your opponents and yes, dare I say it, even over your own team mates providing you’re involved in a team sport and your selection is far from guaranteed.
But let’s not pretend that HIIT is an alien concept to endurance athletes.
You may be surprised to realise that HIIT can in fact encompass as much as 50 – 75% of the total training workload of elite endurance athletes.
After all, what endurance athlete does not want to be better able to deal with lactic acid build-ups?
As already established, what is the superior training method for creating an abundance of lactic acid? Of course, we know it’s HIIT.
Do you imagine that elite distance cyclists such as Bradley Wiggins or distance runners such as Mo Farah simply ride or run all day long to achieve such high levels of aerobic fitness? Not at all!
Olympic gold medallist and Tour de France winner, Bradley Wiggins: “I do the same warm up every time I ride, and have done for ten years. I do 7 minutes working at an easy 60% of my maximum heart rate with a heart rate monitor, then 8 minutes working at 85%. Then I spend the next 5 minutes doing a series of intense 6 – 10 second sprints, interspersed at 95% with easy 20-second recoveries. It’s a routine anyone can follow and benefit from.” And that’s just his warm up.
While not strictly an endurance athlete, let’s also consider double Olympic gold medallist in the 1500m and double silver medallist in the 800m – Sebastian Coe.
While Coe did indeed regularly train at long distances, he was in fact known for utilising a type of interval training back in the 1970’s.
Coe regularly set training sessions where he would carry out 200m sprints with 30 seconds of recovery between each run. As well as that, he would frequently carry out as many as 30 bouts of 100m sprints on a hill. After each sprint to the top – He would simply walk to the bottom and repeat.
Of course, the optimum ratio of CT to HIIT for endurance athletes is a matter of constant debate and is far from settled however, what is clear is that all successful endurance athletes will include a significant amount of HIIT in their training regime.
It would make perfect sense too; if they want to enjoy all the benefits that HIIT brings and in a time frame that CT can’t match or even come close to.
Admittedly, many of these elite endurance athletes will work at the lower end of the high intensity spectrum and for longer periods.
I would say, as I’ve provided evidence for already that these elite endurance athletes would benefit greatly from an increase in intensity and a decrease in duration.
But this debate will no doubt continue.
What evidence do I have for making these claims? Let’s consider VO2 max again and its importance for endurance athletes.
Although VO2 max is associated with endurance work and not short bouts of high intensity, we have already established that high intensity exercise does better improve VO2 max over and above more specific endurance exercise – Quite a paradox when you think about it.
It’s perfectly reasonable to assume that an athlete with a VO2 max of 70 (ml/kg/min) will be able to perform at a higher level and for a longer period than an athlete with a VO2 max of 60 (ml/kg/min).
In a study involving competitive cyclists examining the effects of five different interval training protocols on 40km time trials (17), it was found that the training protocol with both the shortest and most intense interval periods produced the greatest improvements in time along in equal measure with the longest and least intense interval training protocol.
These interesting results could most likely be put down to the longer and less intense protocol being the most specific to the actual time trial they were training for.
With the shortest and most intense protocol out of the five groups ending in similar results, the author of the study expressed his surprise and made the declaration that the improvements in times were most likely down to an increase in VO2 max.
If you’re new to fitness, HIIT or even if you’re a more advanced participant, you’re probably wondering just how HIIT is superior to CT in almost every single way.
It has to do with how we adapt and evolve. For the body to make any physiological changes, you have to place it under stress. Without placing the body under the need to change, it’s not going to change.
By performing CT we just aren’t placing the body under enough stress for it to make any meaningful changes – At least not in an ideal timeframe. CT involves maintaining a steady rhythm that we are comfortable or only slightly uncomfortable with.
When we perform HIIT we are challenging our bodies. We are placing it under severe stress, far more stress than a CT workout would achieve, albeit for a short period of time. Evidently that’s all it takes.
When we run, cycle, row, skip or swim at 100% of our maximal heart rate, we accumulate lactic acid extremely quickly, we feel that burn, we deplete our ATP stores and we use all three energy systems. We therefore force our bodies to make bigger, better and faster changes.
In the interest of fairness, it’s important I list the benefits of CT too. In no way am I putting down continuous training. It is after all a fantastic method of burning calories, although not as good as HIIT, as has already been demonstrated.
CT is obviously better than being sedentary. In addition, in many cases and depending on the individual’s fitness, it may be advised to begin your fitness lifestyle with a few CT sessions just to ease yourself into it.
Even existing HIIT fanatics who train regularly would experience benefits from the occasional prolonged CT workout at 70% of their maximal heart rate.
A varied workout routine is always advised no matter what the participant’s aims may be, and an occasional CT session would provide that same shock or stress to the system that is experienced following those first few HIIT workouts.
Another plus of CT is that it’s essential for a number of sports such as distance running and other endurance based sports.
Yes, even after everything I’ve stated above, of course endurance athletes are still going to train in a manner that is specific to their sport.
However, for the vast majority of athletes, coaches and sports scientists it’s becoming the emerging belief that high intensity interval training is far superior to continuous training.
The only thing that goes against HIIT is the years of fitness industry dogma that advocates for and has always propelled CT.
Let’s take the example given by the American College of Sports Medicine (ACSM) which is the largest exercise science organisation in the world.
In 1995 they updated their Guidelines for Exercise Testing and Prescription, which replaced the earlier guidelines from 1990.
In 1998 these guidelines became the Position Stand for “The Recommended Quantity and Quality of Exercise for Developing and Maintaining Fitness in Healthy Adults.”
They recommended that healthy individuals, in order to maintain their present physical condition should train at an intensity between 55 – 90% (this intensity lowers for unfit individuals) of their maximal heart rate for a duration of between 20 – 60 minutes, 3 – 5 times per week.
More recently, in 2011 they republished their Position Stand reiterating much the same thing.
Except this time they said, “ACSM’s overall recommendation is for most adults to engage in at least 150 minutes of moderate-intensity exercise each week.”
Admittedly and to their credit, they do suggest that this can be achieved either by 30 – 60 minutes of moderate intensity exercise (five days per week) or 20 – 60 minutes of vigorous intensity exercise (three days per week).
Although I wouldn’t necessarily consider the activity “vigorous” if exercise duration approaches 60 minutes.
However, later they state, “Because of the importance of ‘total fitness’ and that it is more readily attained with exercise sessions of longer duration and because of the potential hazards and adherence problems associated with high intensity activity, moderate intensity activity of longer duration is recommended for adults not training for athletic competition.”
Let’s agree that ACSM performs some incredible work (they have over 45,000 members worldwide), they are the global authority in exercise science.
But we have already seen from the research above that “total fitness” is not “more readily attained with exercise sessions of longer duration.”
Consider also that in the same paragraph they appear concerned about potential hazards, perhaps understandable in an age of frivolous lawsuits.
In addition, consider their very genuine concerns over adherence problems (International Health Club Association research shows that 50% of new health club members quit within six months with 90% no longer regularly attending), also stated in the same paragraph, and one begins to sense just why the fitness industry advocates more towards CT than HIIT.
However, the research put forward in this book also demonstrates that HIIT is more enjoyable than CT, not to mention the likely increase in exercise motivation and adherence if people actually knew the other potential benefits they could attain from HIIT.
Put together, all this should mitigate those adherence problems if only HIIT was given the chance and publicity it deserves.
One book entitled Exercise and Fitness Knowledge – Fitness Industry Training Student Resource, quotes ACSM – “The American College of Sports Medicine recommends an aerobic heart rate training zone of 55% to 90% of the maximum heart rate as the exercise intensity necessary to achieve health and fitness training benefits from cardiovascular exercise.”
And doubtless professional trainers having learned from this resource will concentrate their efforts on CT as the primary method for weight loss, achieving fitness and helping clients achieve their dream bodies – And so the cycle continues.
This dogma, also spearheaded by the powerful mainstream media has labelled CT as “aerobic” or “cardiovascular training.”
This has led to the widely held assumption that CT and only CT can condition the aerobic system and lead to an improvement in cardiovascular fitness and a loss of weight.
How many times when you were at school can you remember actually having a dedicated HIIT session?
My assumption is that unless you had a coach on the “fringe” then the answer will most likely be – Never. Yet incredibly while engaging in any number of sports at school, team or individual, you will of course have been engaging in some form of high intensity interval training.
It beggars belief as to why the “link” is seldom made and children from an early age are never taken through their paces with regular HIIT sessions.
Things must change – Today more than ever.
Hopefully things will change and HIIT will become the normal and accepted mode for training in the future. Its superior benefits are clear for all to see.
I hope I’ve proven the superiority of HIIT over CT in the sections above.
It is clear that whenever researchers have compared both training types side by side, not only has HIIT normally matched CT in every category, but it usually far surpasses it.
Not only that, but it does so in a far shorter timescale to add insult to injury.
Once again, given that “lack of time” is the number one reason cited for inactivity and for not starting or sticking with a training regime, I feel that we really do need to hammer home this point.