Blog post

Energy Systems



Have you ever asked yourself why we have training zones? Well, the short answer is, so that you can develop your different energy systems to go further and faster and be more powerful.

The human body has 3 basic energy systems, the Oxidative, Glycolytic and Phosphagen (ATP-PC). Yes it is a mouthful, but hopefully understanding them a bit better will give you some relevance in terms of your training zones. It is also important to note that all 3 energy systems are engaged during all forms of activity, however the ratio that each energy system is engaged differ.

  • During short sharp efforts like a track sprint, the ratio looks something like this: 95% PCr / 3% Glycolysis / 2% Oxidative
  • Longer hard activity like a crit race or XCO race the ratio will be: 20% PCr / 55% Glycolysis / 25% Oxidative
  • And for a marathon event (long road race, gravel or XCM) the ratio is: 5% PCr / % Glycolysis / 90% Oxidative

Off the 3 energy systems the most important and most complex energy system is the Oxidative system. (Aerobic). This system provides basic energy for everyday life. It uses both carbs and fat in a slow energy burn and creates energy in the presence of oxygen. For cycling in general this is the most important energy system as it will drive our efforts over a long duration. And yes, this is why I am so pedantic about you doing your endurance rides in the correct training zone.

On the other end of the scale we have the Phosphagen (ATP-PC) energy system (Anaerobic). This system drives short very hard efforts (10 – 30 seconds) and relies on ATP-PC and creatine phosphate to generate the required energy. ATP-PC is stored in your muscles.

And then, in the middle between these 2 poles we have the Glycolytic system or the Lactic Acid System (Anaerobic). This system uses stored carbohydrates to produce ATP and fuel efforts between 30sec and around 3 minutes (could be longer for some of you).  And if there is not enough oxygen to go around, lactic acid is produced to help push things along. If your body generates to much lactic acid your will get a burning feeling in your muscles and your effort will start to drop.

Ok, so how does this all relate to your training zones.

I use Andy Coggan’s training zones, he uses 7 power zones to deal with the different training zones.

Looking at the training zones and relating it to the energy systems we can join them as follows:

  • Endurance to low tempo: Oxidative system. (Aerobic)
  • High Sweetspot to Anaerobic Capacity: Glycolytic system or the Lactic Acid System (Anaerobic).
  • Anaerobic Capacity to Neuromuscular Power: Phosphagen (ATP-PC) energy system (Anaerobic).

Yes, you will see that I don’t have a match for the pure tempo zone. Off-course training at this zone has an Aerobic system benefit, but is also creates a disproportionate amount of fatigue for the training stimulus benefit you get and it is therefore much better to go down a step and focus on Z2 (endurance).

You will also see that I have changed the pyramid from what you would normally see, and I made the Active Recovery duration MUCH less that the Z2 duration. Active recovery is just that. It is a way for your body to clear some free radicals from your blood after a very hard effort. It is not a training zone. Please do not confuse training in Z2 with active recovery intensity. Endurance training requires a very focused mind. Coffee ride/cruise along the beach = active recovery.

We develop your training plan to develop all of these energy system. For track athletes the focus is more around (ATP-PC) and for E-racing, crits and XCO more around the Glycolytic system or the Lactic Acid System and our long-distance gravel friends the focus is more skewed towards the Oxidative system.

As many of you would know, my coaching philosophy is that of a more polarized approach and to add some spice to this discussion I have added a spreadsheet to will show you the pure 3-zone polarized training zones. To clarify though, although my coaching philosophy follows the polarized approach, it does not mean I don’t see and use Z3 (Tempo and Sweetspot) regularly in my training programs. Depending on where we are on the season, or your time constraints, Z3 still has a big role to play.

Hope you enjoyed my short energy systems / training zones summary. As always, don’t hesitate to reach out to me should you have any questions.


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