Training zones are a way to classify the intensity of our training but they are probably the most confusing metric in running. In my opinion the only people that should be using zones are researchers or coaches discussing training trends over long periods of time. For day to day training and planning training sessions we should forget zones entirely. That might sound like a big call but let me explain .
Let talk about the three zone model first to start to understand the problems with zones.
The three zone model.
In simple terms there is easy running that we can sustain for hours and hold a normal conversation ( Zone 1 ) , there is moderately hard running that we can sustain for 1-3 hours ( Zone 2 ) and there is very hard running that we can sustain for less than approximately 30-60 minutes ( Zone 3).
This model has been used extensively in research as it has some physiological underpinning. Ie there is some basis for arguing there are three distinct training zones from which the body adapts differently to. This is where the 80/20 theory of training stems from. Elite endurance athletes spend 80 % of their training in zone 1 and 20 % in a mix of zone 2 or 3 (its actually more like 90+% in Zone 1 if you define it by time or distance rather than sessions – the original research was based on the number of sessions in each zone; if you did 10 runs and two of them were hard then 20% of them were in zone 2 or 3 yet if we look at time or distance its closer to 10% as the warm up and warm down and recovery are all in zone 1 as well . I discuss this more in the periodisation video) .
The borders of each zone were discussed in the threshold chapter. You will recall there are a number of ways to determine the boundaries of each zone and those boundaries are more transitions rather than distinct borders.
The problem with the three-zone model is the zones are too broad to be used for exercise prescription.
For example for most athletes Zone 3 anything faster than 10km pace. Whether its 100m all out sprints or a park run its all zone 3.
Zone 2 is 10km pace down to about marathon pace.
Zone 1 is anything slower than approx marathon pace.
If we look at a practical example of say a 40 minute 10km runner; the zones would look like this
Zone 1 \< 5 min ks
Zone 2 5 – 4:00 min ks
Zone 3 \> 4 min ks
A zone 2 run could be quite hard or relatively comfortable.
Zone 3 intervals could be all out sprints or 1km reps at just under 4 min k pace
A zone 1 easy run could be very easy at 6 min ks or a more brisk 5 min k pace. The fatigue that results from an easy run at 5 min k pace would be higher than a run at 6:00 min k pace yet it’s all zone 1.
The idea that training adaptions and training stress are the same anywhere throughout a particular zone is just not valid.
Key Take Home
Whilst a three zone model has some scientific basis supporting it , it is way too broad to be used for training prescription.
Because of this coaches have tried to narrow down the ranges of the zones by adding more zones in order to provide a smaller target range.
BUT there is no physiological basis for any more than 3 zones. Models that use 5 or more zones have picked arbitrary numbers to define their zones.
For example
Some common definitions of the zones in a 5 zone model based on max heart rate are
Zone 1 – 50-60 % or 50-65% or < 65%
Zone 2 – 60-70 % or 65-80% or 65-75%
Zone 3 – 70-80 % or 80-85% or 75-90%
Zone 4 – 80-90 % or 85-92% or 90-95%
Zone 5 – 90-100%. or 92-100% or 95+%
( these were from well respected coaches or websites )
You can see there are notable differences between the models.
The idea that we can break down intensity into 5 zones that can be defined as a percentage of a number that does not change with fitness and fits neatly into multiples of exactly 10% is a gross simplification of human physiology and not based on any actual science. It also comes with a very wide error margin .
For example if you are using a formula for max heart rate ( which as we learnt in the heart rate chapter comes with an error margin of +/-10 beats ) and then add to that the different definitions of zones the error compounds even further.
If your max heart rate is 180 +/- 10 beats then zone 2 would be somewhere from 102 to 152 bpm depending on which model you used and allowing for the error margin in max heart rate. Clearly a very broad range and completely useless for exercise prescription
Basing it on threshold heart rate or even better threshold power is better – here are some examples of common 5 zone models used
Zone 1 <85% or 65-85% or < 80%
Zone 2 85% -89% or 85-90% or 80-88%
Zone 3 90% -94% or 90-95% or 89-94%
Zone 4 95% -99% or 95-102% or 95-100%
Zone 5 >100% or >102% or >100%
You can see there is far better agreement between models than using max heart rate. Hence why using threshold heart rate or power is a far better anchor point than max heart rate
Key Take home
Whilst there is some physiological underpinning for a 3 zone model , a 5 zone model is entirely arbitrary with no scientific agreement on the boundaries of the zones .
Zone 2 training ( in a 5 zone model or top end of zone 1 in a 3 zone model ) is a big trending topic at the moment but what actually is it ?
Is it 60-70% of max heart rate or 65-75 % , or is it 85-90% of threshold or 80-88%? Even if you had an accurately determined max heart rate and threshold there is still a wide range of intensities covered by the different definitions. One persons zone 2 might be significantly lower or higher intensity than anothers depending on which model they use.
There is actually no physiological difference between zone 1 and zone 2 – it’s a made up border. Coaches will say zone 1 is for warm up and recovery and zone 2 for building your aerobic base. Is there really any difference between those ? Recovery runs arent really for recovery anyway they are adding more volume with minimal stress to help build your aerobic base. ( see the video on easy runs for a complete discussion on this )
There is no difference between zone 1 and zone 2 other than training load. Eg a run at low end of zone 1 will elicit less training stress than top end of zone 2 – they will both be under the Aerobic threshold , you will be able to hold a normal conversation in both zones and the key training adaptions are the same.
This is only the start of the problem of using zones.
The next major issue is most watches or training software these days will work out your zones for you and tell you if you are working too hard or too easy BUT now we introduce even more sources of error.
First of all different watches / software use different models to determine training zones.
Next we have the issue that a model is only as good as the data it is fed.
What I mean by that is each model relies on several key data points to determine training zones. A determination of either max heart rate or threshold heart rate/pace/power must be made from which to base training zones on.
Let’s say for example your watch/software defines threshold as the highest pace/power/heart rate you can hold for 40 minutes. ( which to be fair is not a bad definition for a good percentage of athletes ). The software will analyse all your data to find the best 40 minute effort you have done and use that to calculate your zones.
But let’s say you have not done a 40 minutes non stop max effort. All you have done is some easy runs and some intervals. The software doesnt know this , it just looks for best effort over 40 minutes . You might have done 8 x 1km at 4min k pace with 90 seconds walk recovery but the average pace over the 40 minutes is more like 5:00min k pace , your heart rate might have been consistently hitting 160-165 in the intervals but average heart rate over the 40 minutes is 150 when you take the recovery periods into account. Using 5min ks or 150 heart rate would be underestimating your threshold hence all your zones will be calculated from that will be lower than what they should be.
Some models require a maximum 3 minutes and 10-15 minutes effort , if you havent done a max 3 minutes effort it can over estimate your threshold and therefore all your zones are set too high.
Key Take home
Unless you
a) know what data your software needs for accurate modelling and
b) have fed the model the relevant data it needs
then your threshold and any zones based on that will be inaccurate.
Then we have the additional problem of inaccurate data , wrist heart rate is problematic , GPS can be patchy in places leading to speeds faster or slower than we have actually run and power can have spikes in it. Unless the data the model uses is valid then any calculations based on the data are invalid.
If you want to use software to determine zones understand the model , feed the model the data it needs and make sure the data is accurate.
Why use zones in the first place ?
Coaches and athletes talk about zones as a means to help set the right intensity for a training session to maximise training adaptions. Yet the 3 zones are too broad and 5+ zone models are arbitrary , not comparable and subject to large error margins.
Hence I argue coaches should forget zones entirely in their discussions with athletes on training intensity. Human physiology is more complex than we would like and our desire to place training intensity in neat well-defined boxes is at odds with what’s really going on.
So if we dont use zones what do we use ?
Keep in mind the reason to use zones is to help guide training intensity. Ensuring our athletes train at the right intensity is of course extremely important – it’s just that using zones is a poor way to do that.
We need to ask ourselves what intensity do we want our athletes training at for a particular run. To answer that we have to understand what training adaption we are hoping to elicit in a run.
Trying to run based on training zones is a backwards way of looking at it. The aim isn’t to train in a particular zone , the aim is to train at an intensity that maximises the training adaptions we are after for in that session. We have got so caught up in zones we have lost sight of the bigger picture.
For example every one is caught up on zone 2 training but the adaption we are after is improving our base aerobic fitness. To do that we need to exercise at an intensity that you can hold a normal conversation at. Some days it will be faster , others slower depending on fatigue levels and numerous other factors but as long as you can hold a normal conversation you are running at the right intensity, ( So if your watch or software tells you that you ran 30 minutes in zone 4 but you could talk comfortably the whole time then your watch is wrong! )
Or if we look at training sessions in zone 3 ,there is a big difference between a workout like
4 x 4 minutes very hard with 4 minutes recovery vs
10 x 3 minutes hard with 1 minutes recovery.
Both seasons are in zone 3 but they are two vastly different workouts. Telling your athlete its a zone 3 workout is about as useful as telling them its a hard session so run fast!
The 4 x 4 minutes session is a VO2 max workout, the 10 x 3 session is a threshold workout. A 40-minute 10k runner may aim to complete the 4 x 4 at around 3:35 min k pace and the 10 x 3 at 3:55 pace. We need to be able to guide the athlete with more precision than we can using zones.
As a coach the first thing to ask yourself when thinking about what intensity your athlete should run at is what training stimulus are you wanting to provide in a particular session. That then guides your intensity prescription.
I will talk in detail on what intensity is optimal for each of the different types of training runs in the particular videos on those training runs.
Key Take homes
Instead of prescribing training based on zones , determine what intensity and duration is optimal to stimulate the desired training adaption.
Using a percentage of an accurately determined threshold is the best means of prescribing intensity.