The physiological basis of the training zones

Any effective training plan uses a variety of training intensities in order to maximise gains. For the coach and athlete, being able to communicate what the aim of training is relies on a classification of exercise intensity hence the ‘exercise training zone’ system.

Unfortunately, one system does not exist that is adopted by all coaches and scientists. In the UK, different ways of classifying training zones are used across the sports of running, cycling, rowing, swimming and triathlon. In this factsheet we present some underlying physiology which should allow translation, understanding, and enable comparisons across any system you come across in the training literature.

The exercise intensity domains

Intensity_domainsAlong the intensity continuum there are important landmarks that cause changes in physiology and will change the body can cope with exercise. The best training zone systems take these landmarks into consideration.

Sport scientists tend to use three main measurements in their description of physiology: heart rate (HR), oxygen uptake (VO2) and blood lactate (BLa). Examining how these 3 parameters behave during exercise allows the stress which the body is under during exercise to be quantified, and has led to the demarcation of exercise intensity zones, or ‘domains’. There are 5 main domains, as described in the table above.

Quite simply, there exists a continuum between being at rest and working ‘maximally’ – although it’s not that simple given that even the phrase ‘maximally’ can refer to different things! Sport scientists tend to use the phrase ‘maximum’ relating to the ‘VO2max’ – the intensity at which the body consumes the highest volume of oxygen that it is capable of in a minute i.e. exercise is supported by aerobic means. Anything above this is ‘supra-maximal’ (like sprinting). The next issue to factor in is that this continuum is not linear. In other words, working at 80% of your VO2max is not necessarily twice as hard as working at 40% of your maximum.

The exercise training zones

Training_zonesSince exercising in each of the intensity domains brings about physiological responses peculiar to that domain, it is therefore logical to conclude that repeated exercise (i.e. training) in each domain will cause different long term adaptations. For this reason, athletes can benefit by having their domain boundaries assessed (by laboratory testing) and the exercise training zones determined. Physiological testing enables heart rates and workloads (power outputs, running speeds) to be assigned for each zone. Table 2 shows how the exercise intensity domains link to the system adopted by British Cycling, and the types of training sessions that can be adopted.

How these zones are used to prescribe a training programme depends on many factors (strengths / weaknesses in the profile, time of year, type of event etc). Other factsheets in the PBscience series provide more details on these issues. However, a well balanced, annual programme should see a combination of work in each zone to ensure all aspects of physiology are developed.

Why are these training zones important?

An athlete could go out and just ride their bike, or just increase their running miles – broadly, this approach WILL get you fitter. However, the fitter you get, and the closer you come to your genetically set limits, the harder it is to carry on fitness (and therefore) performance gains

Using training zones allows you to ensure that you maximise the physiological systems one at a time. It’s a bit like layering a cake, or building a house: you start with a wide base, the foundation upon which to build higher. The common approach is to start in the lower zones, and build the intensity as the racing season approaches.

What training adaptations occur when I train in each zone?

In all truth, the training zones structure can be a little misleading – exercise intensity is a continuum, and although a series of boundaries do exist where the ‘rate’ of physiological differences accelerates, how ‘strict’ these borders are is not evidenced within the research. This means that training in one zone does not give improvement in one system alone; nor does training at the low end of one zone differ drastically from training at the high end of another! You will find more details of the training adaptations associated with each zone in the PBscience factsheets taking each zone in turn. In the meantime, take a look at this summary table to introduce yourself to how the body will react to training above and below the various boundaries.


Table taken from Training and Racing with a Power Meter by Hunter Allen and Andrew Coggan - well worth a read!

Take home message

This factsheet will have introduced you to the markers we can measure in the lab which help set exercise training zones. So, keep in mind:

  • Each training zone gives a range of exercise intensity that will bring about similar physiology: e.g. heart rate response, oxygen uptake, and blood lactate response
  • Accumulation of time in each training zone will therefore bring about specific adaptations...
  • ... although the zones are continuous so there is a large amount of overlap.
  • Layering your training, and using a mixture of training zones at differnet times through your build up will generally bring about the best results over a training year. Read our factsheet on periodisation or check out Dan's presentation on YouTube for more info
  • Using very precise measures of physiology ensure that you hit the right training stimulus in order to bring about the required training adaptations specific to your event.