2×20 Intervals

What are 2 x 20 Intervals?

In summary 2 x 20 intervals are two 20 minute blocks of hard, intense riding divided by a short period of recovery.


The main aim of the 2 x 20 interval workout is to increase your power output and subsequent average speed of your rides. More specifically, 2 x 20 intervals will increase your Functional Threshold Power or FTP. Your FTP can be defined as the maximum level of power you can output constantly for one hour.

Interval Training - 2x20 Intervalsimage by team traveller

Why bother?

So if you’re training for an endurance event like a century ride, why do you want to be increasing your functional threshold power? Well, put simply increasing your FTP will almost certainly improve your all round riding performance. While base training improves your endurance, increasing your FTP gives you more speed and power, no matter how long your event lasts.

Secondly interval training is a great way to control any intense workouts you do in order to maximize your recovery, reduce the risks of over training and injury.



Ideally you need a flat piece of road with little traffic and few junctions where you can be sure to get a good 20 minute period where you have few distractions and can cycle at a hard, steady pace.

Intervals are perfect for indoor training as when training indoors you can train with no interruptions. Secondly the lack of wind, other road traffic and hills means you can perform a more controlled and consistent session allowing you to compare data (heart rate, power output etc) between different interval sessions.


How to Perform 2 x 20 Intervals

There are a lot of different myths around concerning 2 x 20 minute intervals. While there are many variations out there and no one version is ‘better’ than the others I’ll detail below my version of the workout and introduce some basic variations you can incorporate.

There are many different ways to measure your efforts during these intervals (heart rate, perceived effort, % of functional threshold power etc). I’ll discuss these in more detail later in the article but i’ll include below some guideline % of Max heart rates (MHR) to give you an idea.


The Basic 2 x 20 Interval

  • 10 mins steady warm up (75% MHR)
  • 20 mins full intensity (85%-90% MHR, 100%FTP)
  • 10 mins easy pace (65% MHR)
  • 20 mins full intensity (85%-90%  MHR, 100%FTP)
  • 10 mins steady cool down (65% MHR)


When performing these intervals at ‘full intensity’ (as prescribed above) you should only just be able to complete the second interval. By the end your legs should be burning and lungs screaming at you to stop. This should be around 100% (or just over) your functional threshold power (FTP).


Variations of the 2 x 20 Interval

Stating the exact efforts to ride these intervals at is a difficult task. Below i’ll discuss some of the reasons why. By adjusting the gearing you ride the intervals at, you’ll dramatically affect your power output, heart rate and perceived effort.

My main cycling style is to spin smaller gears with a higher cadence and to rely more on my cardiovascular fitness rather than the power in my legs. By altering the gear i ride these intervals in I can massively change what my perceived effort (legs versus lungs), heart rate and power outputs are.

If i push too big a gear I blow up early with aching legs yet my heart rate remains low while my power output will have been high. Increase my cadence in to a smaller gear and my heart rate increases, my power decreases and the effort is on my lungs not my legs.

I like to vary the intervals i ride so sometimes i’ll choose a bigger gear than normal to challenge my strength and try to focus more on increasing my power output. Other times i’ll spin more, working my cardiovascular system more. Once you start doing these sessions you’ll soon get a feel for how you can vary the gearing to achieve different effects.


Why Interval Training Works for Cyclists

By riding 2 20 minute blocks at your max 1 hour power output you’re giving yourself a very tough workout. The recovery in between the intervals means the overall workload is less than if you simply rode for 40 minutes at that intensity with no break.

The big benefit of this workload being less is your body can recover quicker after the training session. This means you’re fresher and fitter for you next training session than you otherwise would have been. Intervals have long been proven to be one of the most efficient ways to make big improvements to your functional threshold power.


When to Use Intervals

When you ride these intervals, and of course how hard, will depend on your training program and your current level of fitness. Usually intervals should only be started in the Spring after you’ve developed a good base fitness.

That said, there is no reason why you can’t perform intervals at any time of the year so long as you allow your body to recover sufficiently afterward. Don’t under estimate how much these short sessions take out of you.

If you know you have a few days off the bike then go hard and maybe ride them at just over your functional threshold power. On the other hand if have a busy week and some big rides coming up then maybe 2 x 20 intervals aren’t the best session for you, at the very least you should ride them at a lower intensity that normal.

Leave a Comment

Previous post:

Next post: