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The how, what and why of interval training

This blog about the how, what and why of interval training teaches you how to improve your endurance performance. What exactly is interval training? And why should you do interval training? What makes interval training effective? How do you design an interval training and how do you best execute it? You will know that at the end of this blog. I’ll also give you tips and tricks for your interval training, so that you learn to swim, cycle and run faster.

My first interval training was in 1990, almost 35 years ago. On the CAV Energie athletics track, led by Alex Halter. I looked forward to it as much as I dreaded it. The training was a series of 200s and 400s. They went fast. The day after, I felt those typical ‘after-interval-track-session-legs’ that I’ve come to appreciate. But what exactly did I train? To be honest, I had no idea.

What is interval training?

The core of interval training consists of blocks at high speed, interrupted by breaks. This way you can run for longer at higher speeds than if you were to run at one continuous speed for the entire training. The Finn Lauri Pikhala was the first coach to have his athletes do interval training in a systematic way. With success, as his pupil Paavo Nurmi won Olympic medals at the Olympic Games of 1920, 1924 and 1928. Emil Zatopek took interval training a step further and won gold at the Games of 1948 and 1952. In the book ‘The Science of Winning’ Jan Olbrecht describes the four building blocks of interval training: 

  1. Number of repetitions
  2. Intensity
  3. Interval duration
  4. Rest between intervals

Het hoe, wat en waarom van intervaltraining - fietsen

These four building blocks allow you to vary endlessly to create interval trainings. Jacco Verhaeren, the former coach of Pieter van den Hoogenband, took pride in never having Van den Hoogenband do the same training twice. Later in this article you will see some sample interval workouts.

Why would you do interval training?

The ultimate goal of interval training is to get faster. In this GCN vlog from June 2024, Olav Aleksander Bu, the Norwegian coach of Olympic triathlon champion Kristian Blummenfelt, says that training in the so-called ‘zone 2’ is overvalued. Previously I wrote on this site about zone 2 training. I agree that endurance training alone will not help someone achieve personal records. I however do not consider zone 2 training to be a waste of effort. Interval training will only pay off if you have a good aerobic base. And you develop that with endurance training. In combination with interval training, you can achieve your best performance. Below are four reasons to add interval training to your schedule.

Four reasons for doing interval training

  1. Improved aerobic and anaerobic capacity: Interval training combines high-intensity blocks with low-intensity breaks or periods. So you train both your aerobic and anaerobic systems. The result: more endurance, more lactate tolerance and/or more lactate production. (You can read further below what the effect of different types of interval training is).
  2. Rapid performance improvement: Interval training allow you to make rapid progress – faster than improving by zone2 training. The reason is your body needs more time to improve through aerobic training than from anaerobic stimuli.
  3. Efficiency: Interval training is time efficient. You can achieve the same or even better results in a shorter time than with long workouts at low intensity.
  4. Mental resilience: Interval training helps you become mentally stronger. You learn to deal with the pain and fatigue that build up during the intervals.

Het hoe, wat en waarom van intervaltraining - lopen

How do you execute your interval training?

You now know the ‘what’ and ‘why’ of interval training, but how do you execute your interval training? Your training starts with the warm-up, followed by the core, and ends with the cool-down.

1. The warm-up

A good warm-up helps you activate your aerobic system and warms up your muscles, tendons and joints, which reduces the risk of injuries. During running or swimming training, you ideally do a number of activation and technical exercises so that you can start the core of the training ‘neuromuscularly warmed up’. Before you start the core of your interval training, you often do a few more accelerations (for running, cycling or swimming intervals), or gradually increase the intensity (for cycling or running intervals).

2. The core

To design the core program, you need to know the goal of your interval training is. More precisely formulated: which system(s) do you want to train? The three main types of interval training are lactate balance intervals, VO2Max intervals, and anaerobic capacity intervals.

a) Lactate balance intervals

These intervals optimize the lactate shuttle, which allows you to better process lactate. In a previous blog I explained that lactate, a residual product of anaerobic energy generation, is not bad. In fact, lactate, together with fats and oxygen, forms the fuel for your aerobic system.

b) VO2Max intervals

These types of intervals increase your maximum oxygen absorption capacity. You improve your heart-lung system and your fundamental aerobic processes. These intervals increase your heart’s maximum stroke volume, your maximum aerobic capacity, and your maximum oxygen uptake. These intervals also increase your lactate tolerance and your body’s ability to store and remove lactate.

c) Anaerobic capacity intervals

Anaerobic capacity intervals increase your maximum lactate production, your maximum anaerobic capacity, your ability to store lactate and the speed of your anaerobic metabolic process. These are the most intensive intervals.

3. The cool-down

After the last interval, do not run straight to the shower, but first do a cool-down. This helps to lower your heart rate, regulate your breathing, remove waste products and relax mentally. Some athletes still do stretching exercises, others do not. Opinions differ on this. When my athletes ask me whether to stretch or not, my answer is: if you like it, you can do it. At least, do it in the right way (which is beyond the scope of this blog).

The how, what and why of interval training: example sessions

Each of the three types of interval training has its own parameters for writing the core of the session. You will find these parameters below, with an example session for illustration.

a) Lactate balance intervals

The parameters for lactate balance intervals are:

  • Number of reps: between 3-12 (or more)
  • Intensity: just below your anaerobic threshold (the intensity at which you can absorb just enough oxygen to balance the production and breakdown of lactate). In practice this means: between your 10km and half marathon race pace
  • Time of the intervals: between 3-15 minutes
  • Rest between intervals: relatively short: between 3 minutes for long intervals (> 10 minutes) to 3-2 minutes for medium intervals (5-10 minutes) to 2-1 minute (for intervals shorter than 5 minutes).

Sample session

4x (6min with 2min recovery + 4min with 2min recovery). Total core: 40 minutes.

Het hoe, wat en waarom van intervaltraining - zwemmen

b) VO2Max-intervals

Thee parameters for VO2Max-intervals are:

  • Number of repetitions: between 5-15 (or more for short intervals)
  • Intensity: above your anaerobic threshold. This allows you to vary in the area just above your anaerobic threshold to well above it: between your 5km and 1500m race pace.
  • Time of the intervals: between 1-5 minutes
  • Rest between intervals: the same length as the interval up to half the interval.

Sample session

3x4min + 3min recovery + 4min block rest: easy jog + 4x3min + 2min recovery. Total core: 24 minutes.

c) Anaerobic capacity intervals

The parameters for anaerobic capacity intervals are:

  • Number of repetitions: between 5-15
  • Intensity: at race intensity of 2-4 minutes length (e.g. running: 800-1500m; swimming: 150-300m)
  • Time of the intervals: between 10-60 seconds
  • Pause between intervals: 3 to 4x as long as the interval.

Sample session

4x1min + 3min recovery + 10min block rest: easy jog + 8x30sec + 2min recovery. Total core: 8 minutes.

The how, what and why of interval training: tips & tricks

Interval training has its pitfalls. Here are six tips & tricks that help you to smartly execute your interval training.

Tip 1) Do one to maximum two interval sessions per week

Interval training requires a longer recovery time than endurance training. Therefore, do one to maximum two interval training sessions per week. That gives you time to recover in between. Recovery is done both passively – sleeping well and lying in the hammock – and actively. For example, through recovery training later in the day or as the first training on the next day. On the other days you can do endurance training to maintain or further develop your aerobic base.

Tip 2) Train, not race: at the end you should be able to do one or two more intervals

When I accidentally joined an interval training with the Ethiopian running top in November 2010, the coach shouted to me halfway through the second interval: ‘TRAIN, NOT RACE’. He was right: I was racing to keep up with the group, not training. In the GCN vlog mentioned earlier, Olav Aleksander Bu gives the wise advice to stop if you feel you can still do one or two intervals. The message: do not completely deplete yourself, but finish the session with a bit of reserve. This way you can also perform your training the next day properly. It also prevents you from physically and mentally exhausting yourself.

Het hoe, wat en waarom van intervaltraining: fietsen

Tip 3) Train at the right intensity

I already explained that there are several types of interval training. Each type has a specific purpose, and therefore specific parameters. That also means that you have to stick to the intensity of the type of system you want to train. That is why I advice to regularly do an exercise test, so that you know what your intensity zones are for your different types of intervals.

Tip 4) Intervals with the group, or alone?

You already know want to get across: if you do interval training with a group, you run the risk of running your intervals too fast or too slow. Usually too fast, because it is oh-so tempting to go with those at the front – who actually may also be running too fast. Remember this Loesje quote: Let your self-confidence be bigger than your ego. If you find it difficult to resist the temptation of the group, consider running your intervals alone.

Tip 5) Periodize your sessions and mix wisely

Too often I see athletes who train multiple systems simultaneously during their interval training. Or to do a lactate balance interval in the first interval of the week and VO2Max intervals in the second. That could have its purpose, but you have to know what you are doing. I prefer to see the type of interval sessions to be consistent for a number of weeks, before changing to the next system. That is core idea of periodization. That is why I also give advice in my  exercise test reports on how to periodise your interval sessions smartly towards your goal.

Tip 6) Create the right conditions

To execute interval training well, you need time, space and focus. My ideal interval starts with 15 to 30 minutes of warm-up running, cycling or swimming, a block of technique exercises and a couple of accelerations. Only then do I start with the core of the session. The core takes between fifteen to sixty minutes, followed by a cool-down of ten to fifteen minutes. If you add everything up, your interval session will take you at least an hour. That means you should plan enough time and don’t rush it.

Also organize space in your training sessions. This is often not a problem for running, but it can be for swimming or cycling intervals. Ideally, you schedule your swim intervals at quiet times during which you have the space to swim your own program and you can start at your own interval time. I know: that is not always possible. My trick is to persuade the other swimmers in the lane to swim with me 😉

Intervals on the bike can be difficult to do outside, because you are on public roads. That is why we have the smart trainer! You can ride that as long and as hard as you want, without the risk of hitting an oncoming fat bike.

High-level interval training can feel almost like a race. You know you’re going to push the boundaries. That requires focus. This implies you should give yourself enough time to mentally prepare for the core of the session. I also recommend my athletes to schedule interval training on their “best” days of the week. That is the day when they are most rested so that ‘they can hit it’. (And yes, there are also reasons to do interval training while fatigued, but I won’t go into that).


Interval training, combined with endurance training, can help you attack your personal bests. Interval training allows you to dot the i’s, increase your threshold values ​​and develop your physical and mental resilience.

A balanced approach, good timing, precise dosing and execution of the core of your interval session and sufficient recovery time are crucial to get the most out of your training.

Happy training!

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