Training Tips

An Introduction to Polarized Training for Runners

on September 08, 2020

As runners we tend to think the harder and faster we go, the fitter we will become. But did you know that running much slower could be the key to running much faster?

Traditional Zones

You will often see pace, power, and heart rate typically divided up into five or six ‘zones’ (learn more about heart rate zones in Zwift). Running in zones 1 and 2 is easy. Running in zones 3 and 4 is harder and running in zones 5 and 6 is very tough.

Many of us end up doing too much of our running in the middle zones, risking injury and increased fatigue over time. Polarized Training is all about reducing your time in the middle zones.

Three Simple Zones

In Polarized Training there are only three zones.

  • Low intensity: you can breathe easily and hold a conversation
  • Medium intensity: breathing is more focused and talk is minimal
  • High intensity: you are blowing hard and cannot talk at all

The aim is to do 80% of your training sessions in the low-intensity zone and 20% in the high-intensity zone. Why the lack of medium-intensity sessions? Because this middle zone is in effect a comfort zone.

As endurance athletes, we race in this zone so we feel we should train in this zone. But while gains can be made quickly here, greater and more sustainable long term gains are made at low and high intensity.

Running mostly at low intensity and spending some time at high intensity gives you the best "bang for your buck" - that is, the greatest increase in performance and recovery time balanced with the risk of injury and fatigue.

How to Divide Workouts

During a high-intensity session, you will likely pass through the medium intensity zones during warm-up, cool down, or interval recovery. That’s fine. You would still count this session as a high-intensity workout.

Furthermore, sometimes it’s difficult to stay in the low-intensity zone without occasionally moving into the medium zone when (for example) running up a hill or doing a particularly long run. Also perfectly acceptable. You would still count this session as a low-intensity workout.

In this way it is easier to split your week into 80% easy and 20% high-intensity sessions.

If you use heart rate to divide your high, low, and medium intensity training, you will find it very difficult to achieve an 80/20 split because your actual high-intensity work will most likely account for only 5% of your weekly effort. That is to say, actual running in the anaerobic heart rate zone will only account for approximately 5% of your weekly effort. So dividing exactly by HR will lead to a 95/5 split, whereas dividing by session will be more like 80/20 because your high intensity ‘sessions’ include plenty of time in the middle zones.

Why Run at High Intensity?

Running at high intensity is where the magic happens. This is where micro-tearing occurs. Muscle fibers break down and rebuild stronger than before. In old money this would be the top of Threshold Zone 4 and into Anaerobic Zone 5.

This is also the zone that will improve your VO2 Max. That’s the amount of oxygen your body can utilize during exercise.

Why Run at Low Intensity?

Running at low intensity is also a magical place to be. This is where mitochondria are formed. They are the energy transfer masters, breaking down nutrients and filling the cells with energy to maintain performance.

The more mitochondria you have, the more energy you can generate. Furthermore, the more oxygen your cells can hold (VO2 Max) the better the mitochondria do their job.

This is also the zone that teaches your body to use fat as fuel more efficiently. This means you can run longer without having to consume too much sugar, which causes so many gastric issues in distance running.

Finally, low-intensity running is less likely to result in injury. It enables the body to recover faster and reduces overall fatigue, allowing you to achieve a higher weekly training volume.

Worth Trying

If you are continually tired after your week’s training, if you suffer regular injuries, if you seem to have plateaued with your PRs - perhaps it’s worth slowing things down. Keep those high-intensity interval sessions, but drop the tempo runs back and don’t push so hard up those hills.

Run slightly longer, but a lot slower. You may just find that Polarized Training is the way forward for you!


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