What Is HIIT?
As the name implies – HIIT, also known as Interval Training (IT) or Sprint Interval Training (SIT) consists of a set number of high intensity exercises, each immediately followed by periods of recovery.
The high intensity exercises can range anywhere from between 5 or 10 seconds to 5 or 10 minutes. Likewise the periods of recovery can range in duration too.
HIIT also enables you to mix up the intensities of your high intensity periods as well as your recovery periods.
By keeping everything varied during a workout, your training session remains considerably more interesting when compared to continuous training (CT).
During the course of this book, I will be referring to CT many times. I’m sure you’re aware of what CT is however, just to clarify CT usually involves exercising at the same intensity for the entire duration of the exercise session.
For example, jogging, cycling or swimming at the same speed or intensity for 45 minutes or more.
To attain the maximum benefits from HIIT, with the least time investment, ideally the high intensity exercise periods should be extremely intense, as intense as you can possibly make them.
They should fatigue you quickly and you should give them everything you have.
However this will only last for a very short duration as exercising at high intensity for extended periods is difficult. This will be due to the rapid build-up of lactic acid as well as a depletion of creatine phosphate (CP) stores, an energy compound in your muscles that powers the body when engaged in extreme high intensity activity.
This combination will prevent you from exercising any longer at your current high intensity, at which point a recovery period will be required.
The recovery period should involve light exercise such as walking, gentle jogging or cycling at an easier pace. This will stop blood pooling in your legs, something which happens following exercise without a cool down.
The recovery period also assists in the removal of metabolic waste products such as lactic acid.
During this time, CP stores will also be replenished, enabling the body to perform high intensity work again, such as sprinting or high intensity cycling.
The recovery period is used to prepare the participant for the next high intensity period of exercise which should soon be approaching.
The variables which can be manipulated during a HIIT workout are as follows:
Duration (time or distance) of high intensity interval. Intensity (speed, resistance) of high intensity interval. Duration of recovery interval.
Intensity of recovery interval.
Number of repetitions of both high intensity interval and recovery interval. Mode of workout (running, cycling, rowing etc).
Why Does HIIT Work So Well? An Evolutionary Look
As living beings, working in intervals is much more natural than working at the same pace constantly. If you think about it, when in our daily lives do we ever work at the same intensity?
From waking up to going to bed, our work rate and heart rates fluctuate all day long. Since our activities change constantly, so does the blood flow around our bodies to supply oxygen and energy to the working muscles when it’s in need.
As we were evolving, our bodies learned to use a greater proportion of energy by performing tasks in intervals over performing the exact same task at a steady and constant pace.
During the course of any one day…
Hunting and gathering, climbing, walking and carrying would all involve intermittent bouts of short bursts of high intensity activity.
In addition, escaping danger would involve the same kind of short burst, high intensity activity.
This was a survival mechanism since we never knew when we would be attacked by predators in such a dangerous world.
Our bodies needed to have an explosion of energy ready for us when we were required to run hell for leather from wolves, bears, other animal predators or even from our deadly spear wielding ancestors from rival tribes.
I’m sure you can relate to the fact that developing the ability to run long distances at a steady pace would not have enabled our ancestors to catch prey or escape predators. However, developing the ability to sprint short distances at an extremely fast pace certainly would have.
HIIT is what comes naturally. It should therefore be no surprise that we experience superior benefits using HIIT over CT.
If you feel the need to relate HIIT to a more modern perspective then simply think about children and what they naturally do in the playground when playing with other children.
Do children play at the same pace for an hour at a time? Or do they instead run around for a few seconds or minutes and then stop for a rest?
Obviously it’s the latter. It’s clear that short bursts of high intensity activity is hardwired into our genetics.
As a consequence and to reiterate, we burn more calories naturally by performing any task in intervals over performing the same task at the same rate for a prolonged period of time.
This is true as long as the interval reaches a high intensity, such as if you were running away from a spear wielding ancestor.
In fact, the higher the intensity the better for your fitness related goals, whatever they are.
Luckily for us, we can apply these principles to accelerating weight loss, improving our cardiovascular system, improving athletic performance and to a range of other exercise related aims.
One of the principal laws of nature as well as human physiology is that we adapt to stress.
By maintaining a constant pace of 70 – 75% of our maximal heart rate for a prolonged period of time, as in CT, we simply aren’t stressing our bodies anywhere near enough to force it to make the rapid changes we’d be hoping for, especially when considering the huge time investment that many of us put into exercise.
However, by reaching a peak of 100% of our maximal heart rate and holding it for as long as we’re capable, if only for a few seconds, not being able to push ourselves any more, feeling the lactic acid building up, burning us and hurting us, this will force our bodies to evolve extremely quickly to better be able to cope with these new physiological conditions.
This is evolution. Let’s use it to our advantage.
Who Is HIIT For?
The vast majority of people will have no problem with HIIT.
The Trained Individual
For those better trained individuals, HIIT will give you a chance to further improve on your gains and at a much faster pace. HIIT will give you a chance to test your capabilities to the maximum.
If you consider yourself cardiovascular trained but have never incorporated any form of HIIT into your training, you should find you’ll take to HIIT extremely quickly and will have no problems adapting.
The sudden extra shock to your system will force your physiology to make those changes to your fitness at a rapid pace which you’ve never experienced through CT.
The Untrained Individual
If you’re sedentary or have little exercise experience then it’s always suggested you check with a doctor before embarking on an exercise programme to ensure you’re fit to take part.
This is true for any new exercise programme, not just HIIT.
I want to make extra certain you understand the above point because the whole idea of HIIT is to work at higher intensities when compared to other forms of training, albeit for shorter durations.
While it’s true that you can carry out HIIT at comfortable intensities when starting out, the aim should always be to be working as hard as you possibly can; 100% of your maximal heart rate.
(Ideally you should also be aiming to hold this intensity too, for as long as you’re able.)
The build- up of lactic acid in your muscles, as well as the depletion of CP stores, will be the deciding factor in just how long you’ll be able to hold this intensity and it will be different for every participant.
You can and should build up to this level, but it has to be understood that this is where you should be aiming to go, and the sooner the better.
Therefore, if you’re an untrained individual, you should start off at the easier end of the difficulty spectrum.
You can do this simply by making your high intensity periods slightly less intense and for a shorter duration.
You can also increase the length of your recovery periods to something that is manageable.
Within a short number of HIIT sessions, you’ll be able to increase the intensity and you’ll be surprised by just how quickly your fitness improves. I’ll provide evidence for this shortly.
For those who are worried about having to reach such high levels of exertion, I will say that there will be times in life when you’ll be required to use bursts of high intensity and all-out effort.
Imagine the next time you’re rushing to catch a train or plane, carrying two heavy bags of luggage. Perhaps you have a family emergency you need to attend to and you need to be home as quickly as possible.
You’ll not think twice about the level of exertion needed to get home under such circumstances.
How about when somebody snatches your bag, wallet or cell phone?
Wouldn’t it be preferential that you had training for when the time arrived?
Of course you’ll leave plenty of fuel in the tank when just starting out and will ease yourself gradually into the all-out efforts of HIIT over a few weeks.
Nobody is asking anybody to become an Olympic athlete overnight.
However, when things become easier for you, as they will do very quickly, you should be expected to increase the intensity and not the duration of the exercise.
Unlike with CT, intensity is the magic word, and not duration. Quality not quantity!
I have read anecdotal evidence from an elderly gentleman recovering from multiple bypass surgery, who after having been cleared by his doctor, took part in HIIT sessions.
The patient made incredible improvements to his cardiovascular system, despite giving up his medication and having complete non-adherence to his prescribed diet. His doctor later told him to carry on doing what he was doing. It appears that HIIT is safe even for people recovering from multiple bypass surgery.
If you’re still worried about the risk from such high exertion due to your age or fitness level, I refer you to a study published in the New England Journal of Medicine.
The study showed that the actual risk from any particular bout of vigorous exercise was extremely low; 1 death in every 1.51 million episodes of strenuous activity.
Furthermore, the study showed that habitual vigorous exercise, such as HIIT actually lessened the risk from sudden death from the actual exercise itself.
One should not be surprised that controlled exercise diminishes the chances of sudden death happening from say, sprinting to catch a train while carrying your luggage.
The Busy Individual
For those people who lead busy lifestyles and are hard pressed for time, HIIT allows you to achieve all the benefits of a longer workout session and indeed more in a far shorter duration.
Due to many years of fitness advice and propaganda, people believe wrongly that to lose weight and to build a healthier body and heart requires a great deal of continuous training, which of course requires a great deal of time.
Studies show that the number 1 reason for non- compliance to exercise programmes is a lack of time. With HIIT, this can no longer be used as an excuse.
If you’re the type of individual who spends much time away on business trips, staying in hotels or on vacation then rest assured that with HIIT, there’s little need for any equipment and in some instances, there’s no need for a great deal of space either.