Understanding Energy Systems and the Fuel They Use

Author: Nick Swanson, Owner and Coach of Through the Wall Training, LLC

In my last article I wrote about the timing of food and how it impacts our recovery and performance.  It is important to understand the energy systems in the body before going into detail about how to optimize your nutrition.  We must first understand what fuels our muscles in order to eat appropriately for training and recovery.  The body has 3 basic metabolic energy systems, which play different roles, depending on the activity you are trying to do.  These energy systems are:

  • ATP-CP, or Adenosine tri-phosphate – creatine phosphate system or phosphagen system
  • Glycolytic system (also known as the anaerobic system or fast glycolysis)
  • Oxidative system (also knows as the aerobic system)


ATP-CP System

The ATP-CP system is the system that is responsible for very short  (i.e. 1-2 repetitions), explosive movements.  This energy system is only good for about 6-10 seconds of activity.  Using cars as an analogy, the ATP-CP system would be your nitrous boost. This system uses ATP that is stored in the muscles to generate power.  The initiation of the ATP-CP system is nearly instantaneous.  Examples of an activity that would utilize ATP-CP are an explosive vertical jump, or a 1-2 rep max lift.


Glycolytic System

Your glycolytic system is what kicks in after your 10 seconds of ATP-CP energy is gone.  The glycolytic system relies almost exclusively on energy from converted carbohydrates from your muscles for energy.  The carbohydrate is broken down into ATP through a complex process and then consumed.  This system doesn’t last very long either; only about 1-2 minutes.  Again, with the car analogy, this is like a racecar – a fast burn of fuel for fast, high intensity activity.  If you are very in tune with your body, when running 200 meters all out on a track, or doing a 30-45 second max effort interval on the bike, you will feel a slight change in your body as you hit 10-15 seconds, and then again at around 35-40 seconds, as your body is transitioning the energy systems being used.   Next time you are doing these types of intervals, pay close attention to how you feel and see if you can notice it.


Oxidative System

The last system is the oxidative system.  This system relies on energy converted mostly from fat and carbohydrate in the presence of oxygen to produce ATP.  This is your Prius.  It doesn’t go extremely fast, but it lasts nearly forever.  The process of generating ATP is more complex than in the ATP-CP or glycolytic systems.  As a point of comparison, the glycolytic system only produces 2 ATP vs. 38 ATP in the oxidative system from the same basic raw materials. This is the system that is the most important to train as an endurance athlete.  However, that doesn’t mean there isn’t a place for doing training that targets your other two energy systems.


Hopefully you’ve now got a better understanding of the various energy systems used in the body, and how they are fueled.   I will go into more depth about the specifics of each in later articles that focus on specific training protocols for each energy system and the benefits of training those systems.  This article also lays the foundation for later discussions about how best to fuel the body and help understand why workouts are designed in a certain way as you go through your Epic Rides training plan.






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AUTHOR: Steve Mokan

Steve is the owner (and founder) of Chasing Epic Mountain Bike Adventures, and contributes regularly to our blog. He's passionate about providing customers with incredible mountain bike vacations, and he loves photography and travel when he's not working. Truthfully, he loves those things when he is working too.

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