In the article about ‘the basics of training’, we already noticed that in prescribing a workout that this is mostly done by power and/or heart rate zones. To get a better understanding about these zones, this article will focus on what these zones are and how to use them.

Why training in zones?
Let’s start with the main reasons to use training zones. By using a power meter and/or heart rate monitor you can specify your workout. By doing so, you make sure you can better reach your training goals and also monitor your intensity. It’s an easy way to make sure you train at the right intensity, duration and do not under- or over-train by doing too much or too little in a training. Afterwards, it is also possible to get a better insight of your training and by doing so monitor your progression and see to what kind of workouts your body reacts the best. Getting a clear picture of what you have actually done in your workouts is the most important starting point to plan your future workouts and specifying zones is a great tool in doing this.

At the moment, there are quite a lot of different distributions of training zones used. Most of them are basically all based around the concept of your threshold heart rate and functional threshold power (FTP). The idea is to name these concepts by 100% and distribute the zones between a certain percentage of the threshold heart rate or FTP.

Three energy systems
But what are the underlying physiological concepts of these distributions? The body basically has 3 energy systems to create ATP , which creates energy and can be used for muscle contractions and thus cycling. These systems are the creatine-phosphate system, the anaerobic system and the aerobic system. The first one is mainly used during sprinting and is emptied after around 15 seconds of vigorous exercise, afterwards the aerobic and anaerobic system take over. The anaerobic system can produce a lot of energy in a short time but also can only be maintained for a short period of time and therefore you must scale down the exercise intensity. The aerobic system uses mostly oxygen and fat to produce energy and is therefore the most sustainable system. So, for maintaining an intensity for a long period of time, like cycling, this is the way to go. However, all energy systems always work next to each other to produce the energy, but depending on the exercise intensity one system contributes more than the other to the energy production. At a low intensity, the aerobic system can free almost all the energy, but if exercise intensity increases, the anaerobic system is used more and more.

Threshold
This is nicely shown during an incremental exercise test. In the beginning your lactate levels, which arise when the anaerobic system takes over, will be close to resting levels. When the power increases, the more and more lactate will be produced. During an exercise test there are basically two important thresholds, which will later explain the defined training zones. The first threshold is called the aerobic threshold, this is the point at which the aerobic energy system is at its maximum energy production capacity. The second threshold is commonly known as the ‘anaerobic threshold’ or FTP. This is basically the last point at which the production and removal of lactate is stable, above this intensity lactate will only accommodate. So, from this viewpoint there are three distinctive training zones: below the aerobic threshold, between aerobic and anaerobic threshold, and above the anaerobic threshold.

Heart rate zones
To translate this concept to heart rate zones, we use five heart rate zones: recovery (60–75%), D1 (75–85%), D2 (85–95%), D3 (95–100%) and resistance (100%–max), all based on threshold heart rate. D1 is below the aerobic threshold, D2 is centred around the aerobic threshold. D3 is just below and around the anaerobic threshold and resistance is above the anaerobic threshold.

Let us dive into the different zones to see what type of exercises are used for the different zones. Recovery is mainly used the day before or after a hard training session or race and, of course, also as recovery between intervals during an intense training session. D1 is an exercise intensity at which the aerobic system is mainly active. The energy production at D1 is mainly dependent on oxygen and fat and by doing so you build your base and endurance capacity.

At D2 around the aerobic threshold, the aerobic system is still the main energy source, but also more carbs are being used. This intensity burns a lot of calories but is best used in longer intervals. By exercising at this intensity, you will burn both fat and carbs. However, training too much and being too monotonous at this intensity will also create a lot of fatigue and probably even overtraining.

Training in heart rate zone D3 is basically training around the anaerobic threshold. This is hard and just barely sustainable. This can only be done when your body is well rested, because D3 will produce excessive fatigue. Training in heart rate zone ‘resistance’ is training above the anaerobic threshold. Therefore, you will only be capable of staying at this intensity for a couple of minutes.

Conclusion
So, here you have the way you can distribute your heart rate zones and how to monitor which energy system you are using. Depending on the goal you have, you can decide to train one energy system more than the other one. Training with a power meter gives the opportunity to monitor your training with even more accuracy, because power lacks the time delay heart rate has and power is less affected by variables such as fatigue, caffeine, sleep and earlier workouts. So, maybe the most important lesson to take home from this article is to use heart rate zones as a great tool to differentiate between the different energy systems, but never ignore your own feelings and use your head!