Zone 2 training….”I can’t run that slowly”…..


It has been given a few names now… “Polarised training”, 80:20, “MAF” but there is a growing consensus that training at low intensity FOR YOU for a significant proportion of your total time is a very effective way of training for an endurance athlete at this stage of the year in particular.

Anyone who has been a member of any of the Triathlon forums on Facebook (“The Ironman Journey” is a major one with 12,000 members) for any length of time will have seen a rash of posts about this time of year that can be summarised as “do I need to train in Zone 2, it feels so slow” “I can’t run that slow” “I have to walk to keep my heart rate down”. Many people seem to understand that is what they should be doing but not generally why. Some people get quite aggressive about it too! “I’ll train the way I always have, it works for me” well, maybe it does so far but are you achieving your full potential and getting the best out of precious training time by minimizing “junk miles”?

But how can running or cycling slower help you do so faster? Hard to fathom but it DOES. The theory seems to have started with the work of Stephen Seiler, an exercise scientist. He studied the training of a range of elite endurance athletes including Cyclists, Nordic Skiers, Rowers, Runners and Swimmers. He found an remarkably consistent factor linking them. They all did approximately 80% of their training at low intensity. This work has since been followed up with specific studies on athletes in the same sport comparing those that trained in this way and those that didn’t showing that those who incorporate a high proportion of low intensity work got better results in testing.

I would have been sceptical if I hadn’t inadvertently proved it to myself. I trained a group of first time half marathon runners about 4 years ago, at their request I did most of their long training sessions with them at a speed considerably slower than I was capable of. My own shorter training sessions continued at a higher intensity. We all ran the “Run To The Beat” Half Marathon together finishing in around 2:40. Around 2 weeks later I ran the Gosport Half in 1:39 – becoming my then PB and considerably faster than I expected to run – without doing any long runs at that pace.

Nobody seems 100% sure of exactly why this works;  I’ll try to keep science to a minimum but a little will help you understand the theories:

The body has two primary energy systems, the Aerobic and Anaerobic systems. In short the Aerobic (“with oxygen”) utilises oxygen Carbohydrates and fat to power activity. It can do so for a very long time as the body even of the leanest athlete has enough fat to fuel several triathlons back to back. The Anaerobic system utilises Glycogen (stored sugar essentially) but it cannot do so for long periods of time as there are relatively limited glycogen stores. Both systems work at the same time but the ratio will vary as intensity of activity changes. Sadly Fat takes longer to process than carbohydrates so the faster the body needs to burn fuel the more it will take from carbohydrates to try to replenish that glycogen.

There are numerous variants on training intensity zones based on key points where physiological changes in the proportion of Aerobic and Anaerobic systems take place – an article on it’s own –  but for our purposes today we need to consider 3 zones:

Zone 2 (“steady”, 73-80% maximum heart rate, 56-75% FTP on the bike, feeling you can go harder, breathing through the nose and able to conduct a conversation) is considered to be the zone in which the body burns 65% carbs and 35% fat.

Zone 3 (“moderately hard”, 80-87% Maximum HR etc) changes the ratio to 80% carbs 20% fat. It is the intensity to race a half ironman or half marathon. The top of zone 3 and into zone 4 is called the “threshold” or “OBLA” (Onset of Body Lactate Accumulation) and signals another physiological change.

Zone 4 (“Hard”, 87-93% Max HR) is the point at which the body predominantly relies on the anaerobic system, burns muscle stores of glycogen and very little to no Fat. It is also the point at which the body generates more lactate than it can use and clear- hence OBLA. It is the intensity for racing 10km and 5km races.

Most trained athletes will, by choice, train  in zone 3 and even if they start at a lower intensity drift into it if not monitoring their heart rate, intensity or pace – it is a mental comfort zone that is not necessarily “comfortable” physically but “feels right” and is where you consider you are putting in a suitable amount of effort (and pride and guilt play a part in this too) but not requiring the pain and effort of training in zone 4.

Desirable results of your training are building the aerobic system and improving the ability of the body to burn fat, adapting to the training load, increasing the mitochondria (little fuel cells) in the muscle cells, increasing the number of blood capillaries, the amount of plasma in the blood and the stroke volume of the heart. The truth is that zone 2 intensity is ideal and zone 3 too hard to achieve those results.

All training causes damage to the system, rest is when adaptation makes the body stronger faster or more able to deal with training loads. If there is less damage the body can concentrate on getting stronger and less tiredness will be carried through to the higher intensity days.

Zone 3 should be avoided as a grey area for training, yes, untrained athletes will see a benefit from training here anyway but this is likely eventually to cause plateauing in training adaptations. Later season race specific sessions will be in zone 3 so your time will come… but it its not the best for building that base.

Higher intensity sessions into zone 4 and beyond form an immensely important part of even long distance race training and should be included in any programme. They will improve your economy, help to develop and use different types of muscle improve general strength and your confidence.

Training in Zone 2 will feel difficult and awkward at first and you will feel a dent in your pride when you see people you know or where you feel you want to show that you are a faster runner, you may even have to accept the indignity of walking up hills, but, do you know what? Nobody really cares and the benefits are well worth it. Call it a zone 2 run on Strava and we will al know! You will get more efficient, you will be able to go faster while still in zone 2 as training progresses and you will maximise your training adaptation.

Since originally posting this blog I have been convinced that amateur cyclists don’t spend enough time training to really reap the benefits and that “sweet spot” “tempo” or top end of zone 3 training allied to hill reps and high intensity work is the most effective.

“If you always do what you have always done you will always get the same results”

DML December 2016


Leave a Reply

Your email address will not be published. Required fields are marked *