The body has three primary ways of creating energy. These physiological pathways are called energy systems. For cyclists, the most important energy system is the aerobic system. However, the anaerobic system plays a vital role in performance too. This article will cover how you use the anaerobic system to put power to the pedals and how you can train it to become a faster cyclist. 

Key Takeaways

  • The anaerobic energy system does not use oxygen to create energy over a short timeframe.
  • Cycling is primarily aerobic, and anaerobic capacity is highly dependant on aerobic fitness.
  • Anaerobic fitness is highly trainable and requires specific high-intensity intervals.

What Is the Anaerobic Energy System?

The anaerobic energy system, also called the lactic acid system, is the body’s way of creating energy in the form of ATP quickly. Primarily using glucose as fuel, this energy system powers the muscles anywhere from ten to thirty seconds for intense efforts. The anaerobic system bypasses the use of oxygen to create ATP quickly through glycolysis. Even though this energy system produces energy rapidly, because of anaerobic byproducts, it is limited due to the excess byproducts. 

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The most important byproduct of this process is lactate. Some of the excess lactate enters the Krebs cycle for aerobic respiration, and the rest is cleared via the bloodstream. As your effort becomes more intense, the amount of lactate eventually outpaces the body’s ability to use and clear it. This balance point is referred to as Lactate Threshold

So what actually limits the anaerobic energy system? The answer is complex and still being studied. However, the current research suggests that it involves your body’s inability to fully use lactate in addition to the familiar sensation of muscular acidosis. The burning sensations are the result of hydrogen ions, which increase acidity in the muscles.

What is Anaerobic Capacity?

As with all of your energy systems, the anaerobic system has its limitations. While aerobic capacity is usually measured in terms of VO2 max, anaerobic capacity is measured in power output during a thirty-second sprint test. Alongside capacity, another important metric is repeatability—how many times you can repeat a hard effort. Both are crucial for performance. The good news that you can increase both your power output and repeatability with the right training.

How Do Cyclists Use the Anaerobic Energy System?

Cyclists use the anaerobic energy system quite often in a ride. It is important to remember that all three of your energy systems are active to some degree. However, it can help to think of the anaerobic system with three different applications, starting, sprinting, and threshold. 

Starting

Every time you start exercising, the anaerobic system kicks in to provide a quick burst of energy before the aerobic system takes over. This is why you have to catch your breath from walking up a flight of stairs even when you are fit. The anaerobic system is creating energy quickly, and then the aerobic system takes over producing energy and clearing lactate. When you are riding, you’ll use the anaerobic system rolling out of the parking lot and resuming your ride from a stop sign. 

Sprinting

This is a power file from a crit race. It shows usage of the anaerobic energy system for over eleven minutes.
An example of cycling power from a crit race with a short 6% grade each lap. This race demanded over twenty anaerobic efforts.

Another way cyclists use this energy system is with quick bursts of power. This is what cyclists typically associate with the anaerobic system. Whether it’s a sprint or hammering up a steep hill, you’re using the anaerobic energy system.  

Threshold

The third way to think about how cyclists use the anaerobic system is with steady-state efforts near threshold. This is when the aerobic system is using the maximum amount of oxygen, and the anaerobic system begins to contribute. This power output level can usually be sustained for 20 minutes to an hour as your body uses the aerobic system to clear lactate. 

Even though the anaerobic system powers the hard surges during a ride, the aerobic system aids in recovery between those hard efforts. As a result, the greater your aerobic fitness, the more power you will be able to produce anaerobically. 

How to Train the Anaerobic Energy System

Training the anaerobic system for cycling is fairly straightforward—complete high-intensity intervals. However, aerobic fitness levels play an essential role. Aerobic fitness serves as the foundation for the anaerobic system, which is why base training is vital. Not only will your anaerobic power be higher, but so will your glycogen storage, which is the fuel for anaerobic efforts. TrainerRoad’s training plans incorporate the requisite aerobic training while including discipline-specific anaerobic workouts. 

Anaerobic Interval Training

Training the anaerobic energy system requires a particular stimulus—repeated efforts above 120% of FTP. These types of intervals activate your type 2b muscle fibers and improve fiber recruitment rate and efficiency. Progressing the number of repetitions will increase your anaerobic capacity and fatigue resistance.

Example Anaerobic Workouts

This is an example of an anaerobic energy system workout that features short, but intense intervals.
TrainerRoad Anaerobic Workout: Joe Devel

A good example of a TrainerRoad anaerobic workout is Joe Devel. Consisting of four sets of anaerobic power repeats ranging between 15 to 45 seconds, this workout helps you build your ability to do a lot of work and repeat it.

Aerobic Energy System vs. Anaerobic Energy System

Both the aerobic and anaerobic energy systems provide the energy your body needs when cycling. There are three primary dividing lines between the energy systems—time, fuel source, and oxygen. The aerobic system uses oxygen, glucose, and fats to produce energy slowly but it can do so for a long time. The anaerobic system creates energy quickly from glucose but only for a short time frame. Even though these energy systems are different, the anaerobic energy system is highly dependent on the aerobic system. Training both will lead to increased fitness and performance. 


For more cycling training knowledge, listen to Ask a Cycling Coach — the only podcast dedicated to making you a faster cyclist. New episodes are released weekly.



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Jesse Fortson

Jesse Fortson lost over 145 pounds with TrainerRoad's help. He uses his experience as a teacher and race mechanic to get faster for crits, gravel, and marathon XCO races.