Training Zones

Training Jun 02, 2022

What are they and why do we use them?

For any endurance athlete who aims to maximise their performance, setting training zones is very important for getting the most out of your training. Training intensity exists on a continuum, with intensity being measured in power output in cycling. By dividing intensity into groups or bands, we get training zones. Training zones are widely used in endurance sports to determine and guide training intensities in order to elicit specific training adaptions. In order to target and drive specific training adaptations, training intensities need to be set in the correct zones for your individual physiology. Doing this will enable you to drive adaptations and enable you to improve specific areas of your cycling performance.

For example, in order to elicit aerobic adaptions that are associated with fatigue, it’s required to work at intensities that maximise the rate of fat oxidation. Similarly, in order to increase your VO2max, it’s necessary to work at an intensity that’s hard enough to elicit close to maximal rate of oxygen consumption.

Training zones are widely used in endurance sports. There are several classic versions and interpretations of training zones. The most common zones you will see in endurance sports are a 3 zone model, 5 zone model, 7 zone model, or even 8 zones. All methods have the same fundamental principles to identify different threshold intensities.

The Science

Here we cover the different energy systems the body uses when exercising, and the scientific methodologies that have been used to understand these systems. These different methdologies each lead to their own classification of these energy systems, and open the door to similar but slightly different zones.  We also cover how coaching practitioners have built on top of these “essential” energy systems, to produce more complex training zones guides

For every pedal stroke we take, energy is required. All energy that is produced to allow work to be done is produced from the breakdown of the molecule ATP. The human body has three major energy systems that can produce ATP; ATP-PC system, Glycolytic system, and Oxidative system. Both the ATP-PC and the Glycolytic system are anaerobic pathways, meaning that they don't require oxygen to produce ATP. The Oxidative system is an aerobic pathway, it requires oxygen to produce ATP.

All three energy systems are engaged during cycling activity, but the extent to which each one is involved varies depending on the duration, intensity, and other factors. To train effectively, you must stress and train specific energy systems that are most relevant to your goal demands and current strengths and weaknesses.

We mentioned different systems in our bodes allow them to do different types of work, and therefore be good at different types of activity - eg marathon vs sprint. We highlighted that we classify these systems using zones. But how should we determine the zones for each individual, so we know the intensity they should work at to drive the adaptation they need, to get to their goal?

Setting Training Zones

There are numerous methods for setting training zones depending on what equipment you have access to. However, here we’ll briefly cover the key physiological principles that define zones.  We’ll take a look at three methods that are fundamental to our current understanding of the body’s responses to different exercise intensities. These are lactate threshold, critical power, and ventilatory thresholds. Understanding these fundamental principles is essential as this is what allows us to calculate training zones without having to do the gold standard laboratory measures.

Lactate Threshold:

  • Considered the gold standard for setting training zones is to use lactate thresholds determined from a graded exercise test. As exercise intensity increases, blood lactate concentrations rises, this relationship is used to identify lactate thresholds.
  • The first lactate threshold is known as LT1 and is used to demarcate moderate and heavy exercise intensity. This threshold is defined as the lowest intensity at which there is a sustained increase in blood lactate above resting values.
  • The second lactate threshold, also known as LT2 or MLSS (maximal lactate steady state is used to demarcate heavy and severe exercise intensity. This threshold is defined as the intensity that causes a rapid increase in blood lactate indicating the upper limit between lactate production and clearance.

The graph below shows a typical result from a lactate threshold test with the 3-zone model.

Critical Power:

  • Another method of determining thresholds is the Critical Power method. This method derives from the concept that the power-duration relationship above a certain ‘critical power’ follows a hyperbolic curve (see image below). It’s been shown that critical power occurs close to the maximal steady state (MLSS).   Critical power demarcates heavy and severe domains of exercise. This test has the benefit that it will also provide information about the size of your anaerobic capacity which is represented as W’.
  • W’ is the amount of work that can be done above critical power. W’ represents your anaerobic capacity.
  • Critical power and W’ can be used as a better alternative to estimating training zones than FTP.

The graph below shows a typical critical power curve with the 3-zone model.

Ventilatory Thresholds

  • Another method of determining training thresholds is by analysing oxygen uptake kinetics. Oxygen demands increase with exercise intensity, the oxygen responses from different intensities can be used to identify training thresholds.
  • The first ventilatory response used to set training zones is Ventilatory Threshold 1 (VT1). VT1  is a marker of intensity at which blood lactate begins to accumulate in the blood. VT1 is  identified at the point where the breathing rate begins to increase.
  • The disproportionate increase in ventilation is the second Ventilatory Threshold 2 (VT2). VT2 occurs at the point where lactate is rapidly increasing with intensity, and represents hyperventilation even relative to the extra CO2 that is being produced.
  • The last ventilatory response used to set training zones is VO2max. VO2max is the maximal consumption of oxygen. It is the maximum capacity of the body to take in, transport, and use oxygen during exercise.

The image below shows oxygen responses to different training intensities.

In line with science, it’s the 3 zone model that is based on robust physiological thresholds and is the most commonly used model in sports science research. This model also relates closely to the domains of exercise.

What does this look like in practice?

The image below highlights all the common training zone models, including the Pillar training Zones. What we can see from the image is that all zone models have a similar relationship with the key physiological thresholds. Even though some have different terminology and the total number of zones, the zone models can be used interchangeably using the physiological landmarks.

  • For all zone models, endurance work is done below the lactate threshold in Zone 1 and/or Zone 2. The zone models with higher breakdowns (5-8 zone model) make the distinction between recovery, easier endurance and higher endurance.
  • In the 3 zone model, threshold work is done in zone 2 and all work done in zone 3 is seen as intensities above threshold.
  • For the 5 zone model, zone 3 is threshold work and zone 4 and 5 break down higher intensities into VO2max and Anaerobic capacity efforts.
  • In the 7 zone model and the Pillar training model, threshold work is split into two, zone 3 and zone 4. High-intensity zones if further defined into 3 zones; Zone 5 VO2max, Zone 6 Anaerobic capacity, and Zone 7, Neuromuscular.

So to summarise all of the above:

  • Training zones are widely used in endurance sports.
  • There are numerous variations of training zones, commonly ranging from 3-8 zone models.
  • Various methodologies have been used to define the energy systems and therefore the training zones.
  • Different training intensities target different training adaptations.
  • Applying specific training zones in your training approach allows you to target specific adaptations.
  • Individualised training zones your specific physiology are required to achieve optimal training outcomes.

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Welcome to Pillar! We’re a small UK-based team (full of real athletes) who are developing an app dedicated to all areas of cycling training. Whatever pains you can think of related to your training, we want to solve them. Pillar is still at an early stage. The first feature we’ve built is an adap…
Welcome to Pillar! We’re a small UK-based team (full of real athletes) who are developing an app dedicated to all areas of cycling training. Whatever pains you can think of related to your training, we want to solve them. Pillar is still at an early stage. The first feature we’ve built is an adap…


Ifan Roberts

Enthusiastic sport scientist, crazy about all things endurance.