What is anaerobic work capacity and W’?


What is anaerobic work capacity and W’?

In a previous article we already discussed the Critical Power model. This model consists of two components. In the Critical Power article we focused mainly on the aerobic component, in this article we will continue with the anaerobic component. This component is especially important during short intensive efforts, think of a short steep climb. Or an attack in the last kilometers of a race.


Anaerobic work capacity (also called AWC or W’) can best be seen as an energy tank that represents the size of the anaerobic energy system. The larger this tank, the more power you can release above Critical Power. More power over short efforts of a few minutes, but this also means more power over longer duration. For example also over your 20minute test as we saw in the previous article. To calculate how much ‘anaerobic’ energy you can release we need to know the exact size of your AWC tank. The amount is represented in an amount of KJ (kilojoules). When this AWC tank is empty you will only be able to ride at your turning point, and you will clearly have to recover before you can go back into the red. The body recovers from an anaerobic effort via the aerobic system, which can, among other things, burn the lactate aerobically and thus ‘recharge the tank’.


By now we know that AWC is very important for (repeated) short efforts. It is therefore easy to think that the bigger this tank is, the better it is. To a certain extent this is true. However, the body is so adaptive that one comes at the cost of the other, so an increase in AWC can come at the cost of FTP. This is because the body produces lactate faster when it becomes more anaerobic; therefore, it will tend to produce more and faster lactate at lower intensities.
Whether that is advisable and important to increase your AWC depends entirely on your goal. If you are training for a long cyclo, it is smarter to make sure you are aerobically fit and you need to focus less on AWC. If you are training for a short criterium of an hour, then releasing anaerobic energy is a lot more important!
For example, if we look at a 20 minute test (1200 seconds), a person with a low AWC (12000KJ) can release 10w ‘anaerobically’ over 20 minutes (12000KJ/1200sec= 10w). A person with an incredibly high anaerobic capacity (36000KJ) can then release 30w over these 20minutes (36000/1200=30w).
If both persons ride 300w average over 20minutes this means a Critical Power of 290w for one and 270w for the other. A substantial aerobic difference!


Because these are very intensive efforts, it is important that you are rested and fresh when you start these trainings. In addition, you should also ensure that you are fully recovered when you start the next repetition, so the rest between the blocks is very long. Think of blocks of 30sec to 2minutes full throttle, after which you cycle for minutes on low intensity to get the acidification out of the legs. Strength training in the gym can also increase your anaerobic work capacity.
The great advantage of the anaerobic system is that it responds very quickly to training, it is really a matter of a few weeks before this system has improved. This is in contrast to the aerobic system which takes much more time to develop.


How important anaerobic energy is depends entirely on your goal. An increase in the anaerobic system can be at the expense of the aerobic system, so it is very important to carefully plan these workouts. Therefore, always make sure that you look carefully in which phase you schedule your anaerobic workouts, and always make sure that you do them fresh and rested! In addition, it is obviously a model where you do calculations of performance and energy systems, it is therefore very important to look critically at your input data before drawing conclusions.
This model and theoretical background can be very helpful in your training approach. Feel free to contact us about what we can do for you. Or check out our training application JOIN which creates a personalized training schedule for you.