Energy System Training

CrossFit is a broad, general and inclusive fitness program.  This means that we hope to be prepared for anything and be competent across broad time and modal domains. Energy system training addresses broad time domains.  From a simplified level, our bodies create energy through three different metabolic pathways.  We can target each of these energy systems based on the length of time and the intensity with which we are working and ultimately train our body to become more efficient at producing energy in each of these pathways. By training in each of these energy systems, we become efficient across different lengths of workouts.  You’re not just a sprinter, and you’re not just a marathon runner.

Anaerobic vs Aerobic

The three energy systems can be classified as either anaerobic or aerobic.  Anaerobic training relies on the creation of energy without the presence of oxygen.  Your body relies on readily available substrates to create a quick burst of energy that can be immediately called upon, but is used up quickly.  Aerobic training utilizes the oxygen that you consume to create energy through a slower energy production system but that lasts for a longer time and continually creates energy as long as oxygen is available and usable.

Anaerobic training can be broken into two categories: alactic and lactic. These two categories rely on two different energy systems.  Alactic training uses the ATP-CP energy system.  In this system, your body uses the readily available creatine phosphate (CP) stored in your muscles to synthesize ATP (adenosine triphosphate) or the energy currency of your body. Lactic training uses what is known as anaerobic glycolysis (or fast glycolysis).  This involves a long chain of chemical reactions to break down of glycogen or glucose to create ATP, or energy in its usable form. This is known as lactic training, because the byproduct of fast glycolysis, known as pyruvate is converted to lactic acid.

Aerobic training relies on the oxidative system, and is the primary energy production of your body at rest or in long, steady-state exercise bouts (e.g. distance running). If there is sufficient oxygen present at the end of glycolysis, the pyruvate is not converted to lactic acid, but is instead shuttled into the mitochondria, converted to Acetyl-Coenzyme A then is utilized in the Krebs cycle going through numerous chemical reactions to create more ATP.  This process can continue to create ATP as long as oxygen and certain other substrates are available.

What it “feels” like: Alactic, Lactic, Aerobic

Despite just receiving a crash course in basic level bioenergetics, it is oftentimes more helpful to understand these energy systems based on how they feel, not by what is occurring on a physiological level (although some may find that helpful).  After all, when you are in the middle of a tough 2 minute interval you aren’t wondering how your body is utilizing glucose, you’re wondering why this hurts so bad!  If you want to know which energy system you are training in, or if you want to make sure you’re “doing it right” and getting the desired stimulus, learn to listen to your body.  Here are the words and feelings we want you to associate with training in each of these energy systems:

Alactic 0-30 seconds  

Think: High, Fast, Short, Explosive.

Feel: Explosive, engine revved up quickly and cooled down pretty quickly

Lactic 30 seconds-2 minutes  

Think: Fast, Power, Extended Power, Power Endurance, Repetition, Interval

Feel: Pain, burn, uncomfortable, hurt

Aerobic Greater than 3 minutes

Think: Sustainable, Long, Cyclical, Flow

Feel: Continuous, steady, sustain

Realistically, there is some overlap between the three systems as you move from one into the other.  Your body doesn’t create energy solely in one system, but we can target which system your body is primarily drawing on by the effort we give within a specific time domain.

Work/Rest Ratios

CrossFit training seeks to increase your work capacity across broad time domains as well as within different modes of exercise.  This means that you aren’t just a sprinter and you aren’t just a marathon runner.  We want to work in short, medium and long time domains, correlating to the different ways your body produces energy.  Our workouts are designed to train your body within specific energy systems and we often do that through work/rest ratios, or interval training.  We work within a specific time domain, and then allow your body to rest and regenerate a specific amount of time so as to stay training in that energy system.  This way, we can create sustainable, repeatable efforts that work more effectively in developing fitness than does 45 minutes on the treadmill at a slow, submaximal pace.