Human Energy Systems and Programming Considerations


When it comes to fitness and physical training there are so many different avenues that you can pursue.

There’s strength training, low threshold aerobic/cardio training, high threshold aerobic/cardio training, power work, sport specific training, circuit training, HIIT, etc.

But if you’re just going for “overall fitness,” what is the best one? 

Or how do you know the correct prescription for each one? 

It’s a difficult matter and it can be overwhelming. 

However, I’m going to simplify this process even more by breaking down each component of the human energy systems to give you a basic understanding of the different forms of exercise out there and then give you some tips and recommendations on writing a comprehensive plan to help take your fitness and performance to the next level.

Let’s get into it!

The Energy Systems 

There are 3 ways for the body to create a muscle contraction, which is the essentially end result of how these energy systems work. 

That’s the goal, muscle contraction in order to pull two connecting bones together. 

Keep in mind, each energy system functions a bit differently for the given demands placed upon the body, but they ultimately have the same goal which is to create energy for contraction.

This energy comes from the food you eat, which is either used immediately or stored for later. 

Below I go into more details about each specific energy system and how they get to the end result. 

The Anaerobic Phosphagen System (*Primarily short duration work)

The end goal of all energy systems is to produce Adenosine Triphosphate (ATP). This system has ATP on hand and available for immediate use. That means when you’re going for a short sprint or about to hit a max lift, you’re using the ATP available in that moment. This system does not use any oxygen nor does it use lactate (a product of glucose breakdown in the glycolytic system). This is your main strength and power system. It will only last for about 10 seconds of hard all-out effort before you use up the current ATP stores. It doesn’t last long.

The Glycolytic System (*Primarily moderate duration work)

Let’s now say you continue to sprint or perform a hard all-out task. Maybe you're doing a “sprint” WOD and you have to slam the gas pedal. This system will start to take over predominantly once you run out of that available energy. The muscle cell will take glucose (simple sugar aka carbs) to produce the necessary ATP for muscle work. It takes this glucose from the available blood sugar and from what’s stored in the muscle cell at the moment. 

*Glycolysis is the process of breaking down carbs into simpler components for energy.

This system will go on to produce lactate (formed from pyruvate), which can then be recycled. Lactate is a good thing since it allows glycolysis to continue to produce ATP and help the production of more NAD+ (which can then accept hydrogen ions, reducing acidity). The acidity is what makes your muscles burn when you’re working so hard. 

In most athletes, this system will operate for about 30 seconds to 3 minutes given the athlete is operating at a level beyond their VO2 Max (maximum oxygen consumption). Therefore no oxygen is being used if you’re continuing to push yourself past the recovery limit. That’s when the muscles burn and you eventually “red line” aka your power output and work performance start to decline and you can’t give anymore effort. You’re above the lactate threshold, therefore lactate levels spike because of how much you’re utilizing glucose and your inability to clear lactate.   

Mitochondrial-Oxidative Respiration (*Primarily long duration work)

This final system is your aerobic system. This one takes place within the mitochondria of the cell and operates in the presence of oxygen to help burn fat and carbs. It will allow you to turnover much greater amounts of ATP (energy), but it takes longer to get that ATP. This system operates at lower levels of intensity, for example a 5 mile run or a slower WOD that you pace yourself for. 

Operating in this system will occur below your lactate threshold since you’re not performing at such a high intensity that you have to kick on the process of glycolysis, creating more lactate. This system uses the electron transport chain complete with molecules and proteins that bond with the hydrogen ions (again, what causes burning in the muscles) and uses them to create larger amounts of ATP. So think low, long durations for this system. Much more efficient for long term work, but not as powerful. Diesel fuel here. 

Programming Considerations 

So now that all the science and chemistry is out of the way, let’s move onto the real-life application. How should we target each of these systems in our training and how frequently?

This can be a loaded question for many athletes out there all having different backgrounds and different goals, but to keep it general let’s focus on the functional athlete who’s moderately trained and is trying to maximize all of these components of fitness.

When structuring their plan, each aspect of fitness is divided into specific buckets. For example, let's use power, strength, moderate-to-high intensity work, low-to-moderate intensity work, and sport specific/gymnastic work. 

From there you can see where each energy system would fall. Strength/power into the phosphagen bucket, moderate-to-high intensity into the glycolytic bucket, low-to-moderate work into the mitochondria/oxidative bucket, and sport specific/gymnastic work into the phosphagen bucket. 

Of course it’s not always that clear cut and these systems are constantly overlapping, but for the majority of the time, that’s the energy system you will primarily be using during that task. 

Now let’s script a general weekly plan based on maximizing each one keeping in mind fatigue and ability to recover. 

For this athlete, let’s pretend it’s a low stress week, training has been going well, no injuries to note, and they work a normal full-time job on top of training. 

*We have to mention that otherwise the plan could be written completely differently, but the majority reading this will most likely have a ton of other responsibilities. 

Monday: Power, Strength, Low-to-moderate work

Tuesday: Sport specific/gymnastic, Moderate-to-high work

Wednesday: Low-to-moderate work

Thursday: Power, strength, low-to-moderate work 

Friday: Sport specific/gymnastic, Moderate-to-high work

Saturday: Power, strength

Sunday: Low-to-moderate work

The weeks are laid out like this in order to minimize the accumulation of fatigue and maximize the athlete’s ability to recover. The moderate-to-high intensity work for the average trained athlete will be pretty rough and can take longer to recover from, hence why it’s only 2x/week. Meanwhile, low-to-moderate work (think steady state cardio) can be performed multiple times a week since recovery will be much greater there. 

For the sake of this, I’m not going to get into specifics with volume and lift selection for the strength and power part, but that does have to be in check and should be monitored week-to-week depending on the athlete's goals. More volume (sets x reps x load) potentially means more fatigue.

Moderate-to-high intensity work will also consist of those tough circuits, WODs, metcons, whatever you want to call them, that have your heart rate consistently at or above that zone 4-5 range. It’s freaking hard work.

Remember, as a functional athlete you want to maximize each energy system so that you’re enhancing your whole fitness package. Going to classes that have you rolling on the floor, gasping for air at the end, time after time, is only focusing on one piece. In order to enhance your performance and health benefits you need to spend time in each bucket to make the changes required. 

Let me know if this blog helped and if you have any questions, leave a comment below or shoot us an email to

As always, we’ll be rooting for ya!




Written by: Phil Gauthier 

Phil is a Doctor of Physical Therapy and Certified Strength and Conditioning Specialist.

He is also an Owner and Co-Founder of the performance gear company, Element 26 (E26).

E26 prides itself on developing functional gear for the functional athlete to help you "Destroy Your PR's, Not Your Body." 

To reach Phil or any member of the Element 26 Staff, please email us at: and we will respond to you ASAP!

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