8 Powerful Truths About High Intensity Interval Training

Within cardio training, there are mainly two different methods to get in better shape: high intensity interval training and continuous cardio training. Continuous cardio training is performed by working aerobically without breaks for a certain period, e.g. 45 – 60 minutes.

You work with a relatively constant intensity during the entire training. Unlike continuous cardio training, interval training is a training type that is divided into intervals consisting of periods of work followed by periods of breaks.

High Intensity Interval Training (VO2 Max.)

High Intensity Interval training man running with high intensity

How long you work or take a break from training can be varied in several ways, and will each give a special physiological benefit. In 8 powerful Truths About High Intensity Interval Training, we will explore this.

The amount of oxygen in the blood is relatively constant. The amount of oxygen we can draw out of the blood is the maximum oxygen uptake, which differs from person to person and depends, among other things on our individual genetic composition – our composition of fast/slow fibers – and training state.

Maximum oxygen uptake and high intensity training

The maximum oxygen uptake is an important factor that describes how good a person is at producing energy using oxygen (aerobic energy). The maximum oxygen uptake corresponds to the maximum amount of oxygen that the body, including the muscles, can absorb from the blood.

What determines oxygen uptake is the heart’s pumping rate, heart rate, the amount of blood pumped around per heartbeat (stroke volume) and the muscles’ ability to absorb oxygen from the blood.

HRM and high intensity interval training

You can also use the heart rhythm, i.e. the heart rate as a guiding factor. Training with an intensity around the maximum oxygen uptake requires a heart rate of about 95 – 98 percent of the maximum heart rate reserve. Use a heart rate monitor (HRM) or the Borg scale for this purpose.

The heart rate all the time must be a little lower than the maximum heart rate, otherwise, the training will be too hard. The training session will be shortened if the intensity is too hard, and thus the training yield will also be less.

Interval training – set your pace

The body can only handle a limited amount of training with such a high intensity. Therefore, it is important to train with an intensity level that improves the maximum oxygen uptake rather than with an intensity that is too hard and may lead to overtraining, or an intensity that is too low and thus a waste of time.

Interval Training Workouts

High Intensity Interval training Exercises smiling female runner

It is not possible to run long distances with an intensity of 95 – 100 percent of the current maximum oxygen uptake. Training that improves the maximum oxygen uptake must therefore be organized so that you can achieve the desired intensity for shorter periods, interrupted by less intensive periods.

Such training is called interval training or interval training workouts, which is characterized by the eternal alternation between intensive and less intensive periods. There are many forms of interval training, and it is actually only the imagination that sets the limits of how to structure the training.

However, it is important to emphasize that even if you perform this form of training with the correct intensity and in the right amount, it is still a very hard and stressful form of training that has a high risk of injury.

What Happens When You Run Interval Training?

When you run interval training, you thus alternate between periods of high intensity followed by breaks of low intensity, such as easy jogging or walking and then shift to high intensity again.

When you accelerate from the breaks to high intensity and run much faster than usual, you stimulate completely different parts of the muscles than you do if you just run a trip at the same pace all the time.

The reason why the tempo changes stimulate the muscles more than a normal easy run at the same pace is that the sprints and accelerations hit both the slow and fast muscle fibers, which we divide the muscles into.

Interval training impacts muscle fibers

The slow muscle fibers develop strength slowly but are enduring. The fast-twitch muscle fibers can be divided into an ‘a’ and an ‘x’ type, with the ‘x’ being the largest, fastest and least enduring. It is the nervous system that controls the muscle fibers via impulses generated in the brain.

The impulses are sent via nerve cells from the brain through the spinal cord to the muscles, which contract and thereby cause movement. Each nerve cell supplies a certain number of muscle fibers, all of which are of the same type, that is, either fast or slow muscle fibers.

The slow muscle fibers are already activated at low running speeds, while the fast fibers become more and more involved as the running speed increases.

At a normal run of 3 km at the same pace, it will primarily be the slow muscle fibers that are active. Whereas in a sprint as at the beginning of a new interval, almost all muscle fibers will be active.

When we start an interval with a rapid increase in pace, all the muscle fibers are set in motion. You achieve to train muscle fibers that will not be trained if you run at an easy pace all the way.

Classic Interval Training

High Intensity Interval training Exercises Classic interval training

So, interval training is a training form where we alternate between work periods and rest periods. Because of the planned rest periods, it is possible to train with high intensity during the work periods. Classic interval training is a structured training form where you determine in advance both the length of work, the length of rest and the intensity of each work period.

Besides, you also choose the number of intervals/work periods in advance. The number depends on the basic form as well as on the length of the selected periods. The pace or intensity of the work periods must be adjusted so that the first and last work period can be completed at the same pace.

Keep the interval pace

If the speed in the first work periods is too high, you will have to shorten the intervals and thereby lose some of the desired training effects.

Interval training is intended as a training form that improves the maximum oxygen uptake. Therefore, interval training is also considered a hard form of training with high quality – high training effects.

However, interval training can also be used in many other contexts, with a much lower intensity, but where a tight structure is maintained. Many training programs for beginners are based on the interval principle e.g. where you start by running for 4 minutes and walking for 4 minutes often spread over 20 minutes of training.

Fartlek/Speed Play as Interval Training

Speed play/fartlek is a more unstructured form of interval training. Speed play is a Swedish invention, where you run more on the feeling than based on a fixed structure. This means that the work periods are not determined in advance, and in the same way the rest periods also vary according to who you run with and where you run.

If you train in a group, the runners in the group can take turns determining both the intensity and length of the intensive work periods. As a result, part of the training will resemble the excitement that is during a competition, where you must always be able to follow the group leader’s tempo changes.

Vary your interval training

If you train alone, you can let the terrain determine the intensity by, for example, increasing the pace between lampposts or side roads. One of the most effective places to train fartlek is in the woods, where changes in terrain, the distance between trees or forest paths can indicate the length of work periods.

One problem with speed play is often the play, the unstructured, which often means that the training will remind about competition too much. The training therefore, risks becoming too hard and thus places great demands on the length of the recovery, which can disrupt the continuity of a training program.

Hill Training

High Intensity Interval training Exercises hill training

Hill training is a kind of interval training that performs on hills or stairs. The structure of hill training can be managed in the same way as traditional interval training. By training on hills improves the strength and power of the buttock’s muscles, calf muscles and the muscles on the front of the thigh.

Hill training is not real strength training, as strength training cannot be performed more than 5 – 10 times before you get too tired. But the buttock’s muscles when you run uphill or on stairs become more powerful. A more powerful starting point means that both the hovering phase and the running steps are improved.

Running on hills or stairs also means that you have to lift your knees higher than when running on a flat road. Higher knee lifts help to increase the stride length and also the stride frequency, which ultimately makes it easier to run faster. The running economy improves too by training on hills or stairs.

Tempo Run 

High Intensity Interval training Exercises Tempo Run Workouts

A tempo run is the classic form of exercise to improve or move the lactic acid threshold. Tempo run includes 20 to 40-minute runs with an intensity equal to or slightly below the lactic acid threshold. A typical training session will include approximately 3 kilometers of warm-up running followed by 5 to 8 kilometers of pace running with an intensity equivalent to the 15 kilometers of pace, replaced by 2 kilometers of cool down.

It is a hard training session that, in addition to the positive effect on the lactic acid threshold, will also provide a mental toughness that makes it easier to cope with hard training sessions or competitions, since tempo run learns the body to run faster before it gets tired. A good solution to complete these pace runs is to use a heart rate monitor to control the intensity.

Tempo runs as test race

A tempo run is also used as test race to prepare for competitive races in the future to test whether you can manage to keep a pace to e.g. a half-marathon. If you train for a marathon, you can also get some good lactic acid training sessions by participating in 5- and 10-kilometer races.

However, you should remember not to run too fast as it will require a longer recovery time and thus limit the training effort several days after.

10-20-30 Interval Training

10-20-30 is the name of a completely new training concept for ordinary exercise runners developed by researchers from the University of Copenhagen. The form of training makes running more fun, halves your training time and lifts your shape to new heights.

10-20-30 training is a form of training where running speed often changes. It is performed in the order 30-20-10. The runner runs at low speed for 30 seconds, followed by a 20-second run at a moderate pace and then a 10-second fast run/sprint.

This takes one minute and is repeated 5 times. The runner then takes a 2-minute break. Such 5-minute periods are performed 1-4 times during a training session.

In other words, it’s Intensive interval training where you run

30 seconds low tempo

20 seconds moderate tempo

10 seconds sprint

So, you run 10-20-30 races the other way around: Like 30-20-10.

Anyone can join. The good thing about this form of training is that everyone can participate because it is a relative load. The whole essence of this kind of training is intensity. It is the intensity and the pressure you put on your body that makes the difference.

Final Thoughts

Interval training has proven to be the most effective training method to improve one’s fitness. This is because you periodically train much more intensively than with traditional distance training and thus challenge the cardiovascular system, joints and muscles much more.

At the same time, it makes you a better and faster runner and as you have read about in this post, there are many ways to vary the intervals, which also makes it more fun to train.

I hope you get something out of this post and if you have any questions about the topic or want to leave your own Personal review, please leave a comment below.

What are examples of high intensity interval training?

High-intensity interval training is a series of exercises with high intensity in fast, short-term activities with small breaks in between. It can be 5x1000 meters with 3 min. breaks between each in running training intervals, or 3 sets (intervals) of 5-8 repetitions in free weight exercises.
Share this Posts with your friends

6 thoughts on “8 Powerful Truths About High Intensity Interval Training”

  1. Hitting the slow and fast muscle fibers and the benefits of it is something I have learnt recently. And I am still doing research about it but I decided to already put it in practice. And I am really seeing results. I feel my body responding positevely to this type of training. Will I go back to how I trained before? Nooo, high intensity is way better!

    • Hi Ann

      Thank you for the comment. Yes, high-intensity training with variation recruits more muscle groups and fiber types, which gives a more resilient strength and a great feeling of surplus. But You also have to be in a certain shape to cope with the loads and avoid injuries.

      Be Well

  2. Hello there! Thanks for sharing this educating and informative article on the truths about high intensity interval exercises. I only partake in random exercises during the weekends, and I must say I never paid much attention to what type of exercise I was doing. Now that I have gotten to know more about interval exercises and their benefits, I think I’ll focus more on them.

  3. Hi Henrik, Thanks for your in-depth article on interval training. It is easy to think of just going out for a jog. Then to add some interval training to it is another thing. But understanding the various types of muscles and the oxygen in your blood has shown me that it is a much more complex idea than just going out for a run. You have given lots of material to digest on high intensity interval training when you are doing far more than just going out for a jog!


Leave a Comment