What Is The Aerobic Energy System: A Beginners Guide [2019 Edition]

Before we get into the aerobic energy system, I want to recommend our most comprehensive guide on athletic training for people over thirty: The Strength Matters System of Athletic Development.

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In today’s article, I’m going to introduce you to the aerobic energy system. I’m going to explain what it is, why you need to pay attention to it, and how to implement it into your own training immediately. For some, this may be game-changing. For others, truly life-saving.


As a reader of this blog and a loyal follower of Strength Matters, I want you to move away from thinking in sets, reps, workouts, and rest periods. To truly reach maximal fitness potential, you have to start thinking about training in energy systems.

This is one of the most important leaps you can make. You’ll move from beginner, or fitness amateur enthusiast, to immediately thinking like an everyday athlete.

Human beings are designed to be aerobic. The more aerobic we are, the more resilient we can be in life. Fear of “losing strength” has reduced aerobic training and popularized anaerobic training (HIIT) in recent years.

However, aerobic training cannot be forgotten.

We prioritize the aerobic energy system above all other energy systems. Such is its importance. It’s the foundational aspect to any training program we do.

A well-developed aerobic system has significant carry over to all other energy systems. It allows people to recover from effort and work faster, and it improves the function of just about everything else that goes on in the body.

Would you like to recover faster between sets and be able to fit more volume into your training? Would you like to burn more fat? Would you like better body composition?

Or in terms of health and vitality, would you like to have an improved immune system? Improved cognitive function? Improved digestion? A stronger heart?

After all heart disease is still the biggest killer.

The list goes on.

We place an emphasis on health above all else here at Strength Matters. And better health starts with a better aerobic energy system.

Human beings are designed to be aerobic. The more aerobic we are, the more resilient we can be in life.Click To Tweet

The Three Energy Systems

There are three energy systems. The body draws on all three, regardless of the type of effort you put in. They merely change in the amount of energy they contribute depending on the duration and intensity of the effort.

They are:

  • The ATP-PC system, or alactic system
  • The Anaerobic glycolysis, or lactic acid system
  • The Aerobic system

Here’s a brief overview of what you need to know about all three:

  • ATP (Adenosine tri-phosphate) is the only energy source for all bodily functions and movements.
  • When ATP is used for energy production, it must be replenished.
  • The body can replenish ATP aerobically or anaerobically.
  • The aerobic system replenishes ATP with the presence of oxygen.
  • The alactic and lactic systems replenish ATP without the presence of oxygen.

I hope I haven’t lost you in science. It can get a lot more complicated than this, but I’m doing my best to make it as simple as possible to understand.

In terms of working timeframes, we’re looking at:

  • Alactic = activities < 10 seconds
  • Lactic = activities lasting approximately 40–60 seconds
  • Aerobic = activities lasting hours

Alternatively, the visual below might help you have a better understanding.

What Is the Aerobic Energy System?

The aerobic system accesses a massive store of virtually unlimited energy. In simple biological terms, the aerobic energy system utilizes fats, carbohydrates, and sometimes proteins for re-synthesizing ATP (cell energy) for energy.

Aerobic means with the presence of oxygen.

It’s a lot more complicated than this, but in essence, think of the aerobic system as using oxygen as its primary fuel source. This energy system can extend out work for hours or sometimes days.

An example of work that would be aerobic would be a 60-minute row, run, or swim. Anything that is classified as aerobic is lengthy in nature, but low in intensity.

Aerobic work is sustainable for long periods of time.

The important word here is sustainable. If it’s not sustainable, it’s not aerobic. Period. And by sustainable, we mean repeatable.

For example, could you run for 60 minutes, rest 10 minutes, and then repeat that same run again? Could you cover the SAME distance in the SAME timeframe?

If not, it’s not true aerobic training.

We Prioritize Aerobic Training Above All Other Energy Systems

There would have been a time when I would have prioritized strength above all else. Everyone needs to get stronger, right?

Well, as you get older and farther away from elite fitness, you realize that health comes first. Without good health, well, nothing else really matters.

Good health is the secret to longevity, and good health lies in training a fully functioning aerobic energy system.

Now, before I offend anybody’s strength training religion, you NEED a base level of strength. We believe in balanced fitness and balanced, healthy everyday athletes who are just as strong as they are aerobically fit.

But when it comes to creating training plans for individuals, we look at the bigger picture in front of us. If someone is as equally strong as they are aerobically fit, we’ll prioritize the aerobic system first. Because the stronger and more robust the aerobic system is, the greater the volume, work and intensity can be. With a superior aerobic system, a person’s ability to recover will be that much greater. Not to mention, a person will be more resilient in life.

It is the same for beginners. If they don’t have any strength or any basic aerobic function, we’ll prioritize aerobic work over strength for them. We need to build their sustainability and improve their ability to recover faster. It doesn’t mean we don’t do strength. Far from it. We’re just prioritizing aerobic system training first to create a fully capable human with balanced fitness.

What could this look like? Well, if we’re looking at a 5-day training week, we’d include 3 days of aerobic-based work and 2 days of strength work.

I repeat, it doesn’t mean strength work is not important. It just means we’re prioritizing the aerobic system first, and it allows us to revisit absolute strength with a more developed, complete system at a later date.

Strength training comes under the definition of anaerobic alactic training. Advanced everyday athletes do have the ability to make weight training aerobic. However, this takes years and years of development.

People spend the majority of their time in the aerobic system. Think about it. Walking, moving, being at work, just living life. A stronger, more robust aerobic system carries over to everything you do in life.

A stronger, more robust aerobic system carries over to everything you do in life.Click To Tweet

However, here’s the problem.  Most people in today’s society have completely lost the ability to perform basic aerobic sustainable functions. Walking is a great example of this.

Biologically, humans are set up to “go long” or sustain work for extended periods of time. However, this is no longer the case in society. Modern society is allowing us to become lazy. We don’t have to walk as far. We take elevators instead of stairs. We drive short distances to get to our destinations. We sit more than we stand.

We want to do shorter, more intense workouts. (Don’t get me started on HIIT training.)

The list can go on and on. Nothing highlights this more than living in a ski resort and seeing people’s fundamental lack of ability to walk around the resort.

If you haven’t read this blog post yet, I’d highly encourage it:

The #1 Thing I’ve Learned Living In A Ski Resort

How We Assess Basic Aerobic Capacity

When people start working with us, we always go through the same assessment process. Health first, then movement, and then basic strength and aerobic capacity.

If you’d like to learn more about our health assessments click the link below:

The Strength Matters Health Assessments

We have complex aerobic capacity assessments. However, people have to earn the right to unlock these, but they must first demonstrate good levels of strength AND basic aerobic capacity.

When it comes to basic aerobic capacity testing—and I emphasize the term basic aerobic capacity testing because this is just a snapshot of an individual in the initial testing phase—we have a number of options.

The 10-Minute Assault Bike Test

We always start with the 10-Minute Assault Bike Test, maximum calories in ten minutes.

This is great for beginners, intermediates, and advanced alike. It’s a simple test that almost anyone can perform. There is virtually no requirement to learn technique, unlike running or rowing.

The ability to control aspects of this test and provide valid, repeatable results allows us, as coaches, to clearly notice patterns in performance, and compare and contrast those patterns to other everyday athletes.

It’s not a true aerobic capacity test. It’s just a 10-minute work capacity snapshot. But we learn a lot about an individual in 10 minutes.

When analyzing the results of this test, it’s important to take into consideration the bodyweight of an individual.

A 137 lb female, who scores 100 calories in 10 minutes, compared to a 210 lb male who scores the same, shows that his work rate is significantly more inefficient as he is using more bodyweight. It’s not all about the calorie score, but we monitor and track this over time to see improvements with each individual.

Not everyone, however, has access to the assault bike. If that’s not an option, we have other options, but it comes down to a coaching decision and is based on experience.

Alternative Basic Aerobic Capacity Tests

If the assault bike is unavailable, we progress to other types of testing based on the experience of the individual and the goals. We have three more options:

  • The 20-Minute Walking Capacity Test
  • The 2 km Row Test
  • The 5 km Run Test

The 20-Minute Walking Capacity Test

This is quite possibly the most fun and deployed test that we do for people who start working with us. After analyzing hundreds of clients’ data around steps in addition to our general observations, we’re coming to realize that people are losing the ability to walk for long periods of time.

For people who are new to fitness or new to aerobic capacity work, we often deploy this alongside the assault bike test, even when the assault bike is present. It becomes a foundation for everything else that we do.

The test is simple. Choose a route that’s repeatable and has no obstructions. Start from the same point each time and set a timer for 20 minutes.

How far can you walk (in miles) in that 20-minute period?

Walking just so happens to be our starting point for developing aerobic capacity, and for many, this becomes a fun weekly test.

The 2 km Row Test

If the assault bike isn’t present and the training age of our client is that, that they demonstrate enough experience with a Concept 2 rower, we deploy the 2 km row test.

Simply how fast can you row 2 km? Again, this is not a true aerobic capacity test, but we can pull the data from the Concept 2 site and analyze/compare it to that of other people around the world.

It’s not our preferred choice because of the skill required in rowing technique, but it’s a great test none the less. For beginners/intermediates, it’s a tough test. For advanced, yeah, it sucks because we know we can go so much deeper into the CNS, which can totally destroy you. It’s a test that we dread to see when it comes up.

The 5 km Run

The 5 km run is only deployed when people have the basic movement and baseline strength levels nailed down, and the option of an assault bike and rower isn’t available. This 5 km run is also used when the athlete’s experience means that the walking test is not suitable.

It’s a test for highly skilled individuals, and it has the highest risk for injury. It’s important that we own the movement and the skill of running first.

It’s a fun test, only to be deployed in special circumstances. 

How Do We Train the Aerobic Energy System?

The aerobic system can be trained through a cyclical or mixed modal approach. Cyclical means things like walking, running, swimming, biking, rowing, etc. Mixed modal means using a number of modalities, similar to that of circuit training.

For people who are new to developing the aerobic system, we start with the cyclical approach first. It’s easier to implement and easier to track. Mixed modal is very much dependant on somebody’s training age and abilities in a given task. We use that method for intermediate to advanced individuals.

In principle, we like to progress people from aerobic endurance to aerobic power. That means the pace of work tends to progress from slower to much faster contractions. We focus on training aerobic intervals that are 25% of the timeframe of the goal in mind.

For a 4-hour marathon race runner, we would deploy interval training of 60 minutes. A 5 km race runner, there would be intervals of 5 minutes if they were aiming for a 20-minute pace.

Once we decide on the interval pace, we then approach the training plan in the following manner:

  1. Under pace
  2. Increase volume
  3. Increase pace
  4. Reduce rest

Nearly all people we work with start with 60-minute intervals. It’s only over time, often years, we progress down to much faster contractions that would involve 30-second interval repeats.

To develop a fully-fledged aerobic energy system, you need to build the base of support so that you can go deeper into the nervous system to elicit better results, thus the faster the contractions become.

Think of a manual car. You don’t want to just use one gear, right? You want to develop competency using all the gears. Most people think aerobic capacity involves working on faster intervals – 30 seconds on, 30 seconds off, and repeat. That trains only in first gear. What about fifth gear?

You need to earn the right to get to faster intervals, and that means starting with slower contractions and longer durations first.

When training true aerobic intervals, you need to demonstrate repeatability. The aerobic intervals are 25% of the time of the race goal. If we’re practicing for a 4-hour marathon time, our 60-minute working interval should be so much so that you could continue for a further 3 hours.

You shouldn’t be crawling around on the floor gasping for breath. That’s not aerobic training. Aerobic training is about sustainability and repeatable efforts.

But here’s the problem. The vast majority of people have never done 60 minutes of sustained aerobic work before. More often than not, we need to get people to adapt to 60 minutes of sustained work effort, and that often starts with simple plain-old walking.

Walking: A Sample 12-Week Plan to Better Aerobic Capacity

For people who have never run before and are looking to do a 5 km race for the first time, this is our preferred method of building their aerobic capacity before actually running. Most people who decide to run 5 km have never actually walked it before. So guess what, we get them to walk it first.

It’s also a great plan for people who have been lifting weights all their lives, and they realized that they now need to do something about their high resting heart rate and high blood pressure.

Before trying this program I’d recommend testing your 20-minute walk capacity test and resting heart rate. Then, once you’ve completed the program, retest to see the improvements made.

This is our preferred method of building somebody up to a sustainable 60-minute aerobic interval.

Week 1:

3 x Week
20-Minute Walk Capacity Test.
How far can you walk in 20 minutes?

Week 2:

4 x Week
20-Minute Walk Capacity Test.
How far can you walk in 20 minutes?

Week 3:

5 x Week
20-Minute Walk Capacity Test.
How far can you walk in 20 minutes?

Week 4:

3 x Week
40-Minute Walk Capacity Test.
How far can you walk in 40 minutes?

Week 5:

4 x Week
40-Minute Walk Capacity Test.
How far can you walk in 40 minutes?

Week 6:

5 x Week
40-Minute Walk Capacity Test.
How far can you walk in 40 minutes?

Week 7:

3 x Week
60-Minute Walk Capacity Test.
How far can you walk in 60 minutes?

Week 8:

4 x Week
60-Minute Walk Capacity Test.
How far can you walk in 60 minutes?

Week 9:

5 x Week
40-Minute Walk Capacity Test.
How far can you walk in 40 minutes? 

Week 10:

3 x Week
60-Minute Walk Capacity Test.
How far can you walk in 60 minutes?

Week 11:

4 x Week
60-Minute Walk Capacity Test.
How far can you walk in 60 minutes?

Week 12:

5 x Week
60-Minute Walk Capacity Test.
How far can you walk in 60 minutes?

Twelve weeks of walking. For some, this will be both game-changing and life-changing. It’s also the start of getting people to truly train the aerobic continuum.

Health is so much more than working out inside a gym. This can be deployed in conjunction with a healthy strength training routine. Combine the two, you’ve got a winning weight loss program.

The art of sustained work is quickly being forgotten. Life does not revolve around 5-minute HIIT training sessions. Training for a healthy, resilient life starts with training the aerobic energy system in a progressive systematic manner.

Closing Thoughts

In recent years, the aerobic energy system has become the enemy of the fitness world, in favor of the alactic and lactic anaerobic methods. It shouldn’t be forgotten. It’s a vital system that is an evolutionarily efficient way for humans to produce energy. Aerobic training is the foundation for everything we do in life, and it has huge benefits to the cardiovascular system, lungs, and muscles in developing thriving longevity.

Heart disease is still the biggest killer in the world. Health comes first at Strength Matters, and that to us means the Strength of your heart Matters. It’s why we prioritize the aerobic energy system above all other energy systems.

Develop it the right way, and you’ll never look back.

The High-Performance Handbook for Everyday Athletes Over 30

Learn the world's most effective training system for people over thirty who want to look better, feel better, and perform better.

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Life’s better as an everyday athlete. ~ James Breese

About The Author

2 thoughts on “What Is The Aerobic Energy System: A Beginners Guide [2019 Edition]”

  1. Thank you James. Excellent article. You increased my understanding of the 3 energy systems because of the simple way you broke it down and explained it.
    I’m coaching my grandsons. They run the 3200 and 1600 meters in HS track. I took Phil Maffetones course last summer and we applied his emphasis on developing the aerobic system while we worked up to 80 mile weeks in the mountains in Colorado. At first, to stay aerobic, they had to walk up the hills a little. They wore HR monitors to track their HR
    After 2-3 weeks the walking stopped and every week their times dropped while the HR and running route stayed the same. My senior won a Texas State Championship in XC.
    Now we’re in track season, seven weeks from the State meet. They’ve continued the aerobic running throughout the winter. We have been doing Threshold, critical velocity (from Tinman Tom Schwartz) , and short fast intervals to build aerobic power and endurance.
    Are the fast (800m pace) intervals at 300, 400,, and 600 meters with 3-5 minutes rest enough to develop anaerobic strength? Are there workouts for middle distance runners you would suggest?
    I am looking forward to the next article about training the lactic energy system.
    Thank you

    1. Thanks for you reply Karl! Strength would need to be done in the weight room. You can do hill work and repeats, but it’s not quite the same. We have to think of the body as one unit and do core too… I wish there was a simpler answer! Have you read our book Maxium Aerobic Power? There are a ton of workouts in there that might assist… Good luck with the track meets!

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