Energy production and management are the core of endurance sports. Your body has three main energy systems that enable you to put power to the pedals—aerobic, anaerobic, and PC-ATP. In this introduction to the different energy systems, we’ll cover how they produce energy, how they are different, and why they are essential. 

Cellular Energy

ATP or adenosine triphosphate is a molecule that your cells use for energy. Produced by mitochondria in the cells, ATP releases stored energy that fuels the body. The more ATP your body can produce, the greater your cycling performance. 

Each energy system produces ATP in different ways based on how quickly your cells need energy. The good news is that you can train each energy system. With the right structured training, the body becomes more efficient and effective at creating ATP.

Aerobic Energy System

The aerobic energy system is the superstar of cycling and provides most of the body’s ATP. The aerobic system is the slowest in creating ATP and fuels efforts longer than a couple of minutes. Through the Krebs cycle (also referred to as the citric acid cycle), your body produces ATP using oxygen and either glucose or fatty acids. 

When cycling, the aerobic system is the primary power producer from standing still to the point that your cardiovascular system cannot utilize any more oxygen (VO2 Max). In terms of the cycling power zones, this includes active recovery, endurance, tempo, sweet spot, and threshold. 

However, just because you start riding above your threshold doesn’t mean your aerobic system turns off. The aerobic system continues working to help process the by-products of the other two energy systems. 

Anaerobic Energy System

The anaerobic energy system produces ATP rapidly and doesn’t require oxygen. This system is the primary power producer for intense efforts lasting thirty seconds to around three minutes. Anaerobically, your body converts glucose into ATP and pyruvate. The pyruvate is then converted into ATP or lactate. 

During a ride, you begin to use the anaerobic energy system anytime you tip over your FTP. Usually, you can feel when your anaerobic system is working hard because of the burning sensation in the working muscles. Related anaerobic power zones include threshold, VO2 Max, and of course, anaerobic capacity. 

ATP-PC Energy System

Technically, this system is called the phosphocreatine energy system. For simplicity’s sake, most cyclists just refer to it as the neuromuscular power zone because that is its primary application. This energy system uses creatine phosphate to produce ATP quickly and does so anaerobically. It also provides energy without producing lactate, so it’s also called the alatic system. The ATP-PC energy system powers maximal efforts lasting less than fifteen seconds.

The ATP-PC energy system is what fuels your max sprint power and short bursts. While this system produces energy quickly, it requires extended periods of recovery. This is why you have to rest in between sprint efforts.

Aerobic vs. Anaerobic vs. Neuromuscular

Each of the three energy systems provides the energy your body needs when cycling. While each one produces ATP differently, the end goal is power to the pedals. There are three primary dividing lines between the energy systems—time, fuel source, and oxygen.

The aerobic system uses oxygen to produce energy slowly but can do so for a long time. The two energy systems that use anaerobic processes exist in a much shorter time frame. It’s important to remember that cycling is mostly an aerobic sport. When you are creating energy anaerobically, it doesn’t mean your aerobic system turns off. Repeated anaerobic efforts increasingly become more aerobic. For this reason, building your aerobic base is crucial for endurance performance. 

Training each energy system requires a specific stimulus and is related to each of your power zones. Riding in each zone sends a unique signal to the body, which then drives adaptation. Every TrainerRoad training plan targets the energy systems that you’ll need for your event. 

More on Energy Systems

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References and Further Reading