Onward and Upward: ‘Energy Systems Explained’

You have probably seen terms on the whiteboard like lactic power, lactic endurance or aerobic endurance. I am sure that most of the time it leaves you with more questions than answers. We wanted to take a moment to help explain a little better and hopefully give you some info to help impress your non-CrossFit friends as you discuss your fitness.

As a living, breathing, blog reading individual (and hopefully member of CrossFit Cornelius) you’ve probably learned the basics around how food provides the body with energy. There are actually several different ways that this can occur and they depend on the activity being performed.

Depending on our sport or activity, nutrition, genetics, and level of training will each play a role which energy system is primarily utilized. Regardless of which energy system is predominantly used all energy is stored in the form of ATP.

Adenosine Triphosphate or “ATP” is the energy currency of the body. Each of the energy systems in the body have their own way of producing ATP to power our daily activities. There are pro’s and con’s to each energy system but ultimately having a better understanding of how our body uses energy can help us make informed decisions on diet and exercise.

We feel its best to test all of these systems to help keep moving your fitness forward on a regular basis.


Let’s learn about each energy system…

Alactic System aka “the Creatine Phosphate System”
Lactic Acid System aka “Glycolytic”
Aerobic System aka “Fatty Acid Metabolism”


“You don’t have to see the whole staircase, just take the first step.”              – Martin Luther King


Alactic System

(aka the Creatine Phosphate System)
What is it: The alactic system utilizes creatine phosphate (CP) as an energy source. It fuels high intensity efforts. Creatine is able to donate its phosphate molecules to the the Adenosine Diphosphate (ADP) molecule allowing it to return to ATP, with potential energy stored in its chemical bonds. Creatine comes from the food that we eat with the highest levels in red meat, pork, poultry, and fish. It can also be supplemented for vegetarians and vegans.

Time domains: This energy system is exhausted in 8-12 seconds for most individuals and you will fatigue when your CP and ATP stores have depleted. It is great for quick bursts of energy.

Efficiency:It requires 30 seconds to 2 minutes to replenish energy stores.

By-products: Heat released from the breaking of chemical bonds.

Examples of activity: You may see this energy system in action through the short powerful bursts seen in weightlifters, powerlifters, pitchers and shot putters.
What training looks like: Training the CP system means using short time domains with long rest periods in between. In the gym this means keeping rep ranges to sets of 6 or fewer reps.


Lactic Acid System

(aka Glycolytic system)
What is it: The lactic acid system utilizes glycogen (glucose stored in the muscles and liver) as a fuel source. It is for longer lasting high intensity activities. Our body is able to store about 500 total grams of glycogen in the muscle and liver tissue which provides around 2,000 calories worth of energy. Running out of this fuel source is commonly referred to as “bonking.” Some athletes consume carbohydrate foods, drinks, and supplements during training and competition to prevent running out of this valuable fuel source.

Time domains: It is the primary fuel source for activities lasting from 30 seconds to about 3 minutes. You know you have fatigued this energy system when hydrogen ion accumulation causes a burning sensation in the muscles.

Efficiency: The lactic acid system is very efficient at providing fuel but fatigues quickly. Due to the long recovery time it is favorable to alternate levels of intensity between glycolytic and aerobic dependence to sustain high output.

Byproducts: The byproduct of this system is pyruvate. Which must be cleared from the blood to continue to utilize this energy system. This can take 30-60 minutes.

Examples of activity: This energy system would rule during a 400 or 800 meter sprint or a hockey lines time on the ice. It is seen in mixed use with the aerobic system during longer workouts or soccer and basketball games where the players alternate between a slower jog pace with periods of intense sprinting and jumping.

What training looks like: To train this energy system you can utilize interval style training. Intense bursts of energy followed by a recovery period that allows you to stay at a threshold of high output. These athletes tend to have increased muscle mass and ideally lower body fat percentage.


Aerobic System

(aka Fatty Acid Metabolism aka Krebs Cycle aka Citric Acid Cycle…)

What is it: This is the creation of energy from fat, glycogen or protein in the presence of oxygen used to power low and moderate intensity activities. The mitochondria present in muscle cells takes the available fuel source through a variety of reactions to produce ATP. Since fat molecules packs 9 calories per gram they tend to be the main choice for this energy system. Even the leanest individuals carry enough body fat to fuel many days worth of activity.

Time domains: Any activity lasting more than 3 minutes in duration.

Efficiency: This system produces energy much more slowly than the others. The good news is it can utilize an unlimited fuel supply of fat.

By-products: The aerobic system only produces water and carbon dioxide when generating ATP.

Examples of activity: This energy system is your predominant fuel source for jogging, cycling, swimming long distances, and most of your daily activities.

What training looks like: Athletes who have become efficient at using fat as a fuel source are able to convert the energy from fat more quickly, allowing them to sustain higher levels of work capacity for activities with long durations. These athletes are usually easy to spot as they have exceptional muscle definition and extremely low body fat.

By training in all three energy systems we can become more efficient in all areas, thus increasing our work capacity across the board. Individuals who only try to utilize cardio or lifting heavy weights to improve work capacity will fall short of their well rounded counterparts. If you’re an individual who wants to improve general health it is beneficial to train each of the energy systems. This is exactly why we use all 3 systems during our class programming to help ensure you are staying as well rounded as possible.

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