June 12, 2026
I often say I help people build "real fitness" in my 1:1 coaching.
What do I actually mean by that, though?
I define it as being developing all aspects of your fitness; not just one.
That begs the question: what makes up your "fitness?"
Primarily:
Strength
Aerobic fitness (conventionally called 'cardio' or 'endurance training')
Anaerobic fitness
Power
Mobility
Anaerobic fitness is among the most important on this list, but it doesn't get nearly as much attention as the others.
This newsletter will cover what it is, why it matters, and how to train it.
For a deeper dive or a video version of this content, go here.
Anaerobic means 'without oxygen' and aerobic means 'with oxygen.'
When you do any sort of endurance or conditioning work, your body is either deriving its fuel from anaerobic or aerobic energy systems. [1]
There are a few key differences between these different means of producing energy.
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First: they differ in how quickly versus how much and for how long they can produce energy. [1]
Your anaerobic energy systems can produce energy much faster, but your aerobic energy systems can produce a lot more and for a lot longer period of time.
The anaerobic systems become useful when you need energy produced at a rate that your aerobic system can't keep up with (such as high intensity running).
These anaerobic energy systems are your predominant source of fuel during activity where you hit fatigue within approximately 1–4 minutes.
In other words, a 400 meter run done at maximum effort would be anaerobic while a 5k run done at an easy to moderate pace would be an aerobic run.
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Second: your anaerobic energy systems differ from the aerobic ones in that they produce lactate and acid within the muscle. [1]
As this acid builds up, it will inhibit further muscle contraction and energy production.
Thus, one of the main ways your body gets better from anaerobic training is by being more efficient with the clearance of lactate and the buffering of acid.
Anaerobic training is truly the foundation of any conditioning program.
That is, it arguably should be prioritized before you program other forms of conditioning (such as zone 2 cardio...).
Obviously, performing anaerobic conditioning will make you better at activities that are dependent upon anaerobic energy systems. However, the benefits stretch beyond this.
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When you do any sort of endurance work, you are typically using all of your available energy systems at the same time; it's just a matter of which one is contributing the most.
That same lactate and acid build up we mentioned before can also inhibit your body's ability to produce further energy and muscle contractions from aerobic processes.
So, the better your body is at clearing lactate and acid from the muscle, the more "freed up" your aerobic energy systems are going to be.
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Moreover, this is the exact sort of process your body does when it is recovering in between sets of strength training.
The reason you need to rest ~2-4 minutes in between sets of squats (for them to be of high quality) is so that your body can clear all of these built up metabolites.
The better your anaerobic fitness is, the more effective and efficient your rest periods will be. This will make each set that much higher quality over time.
It isn't conjecture to say that true anaerobic conditioning is one of the most health-promoting types of exercise.
The adaptations your body has to make in order for your performance to improve are the same it has to make for improved health.
Some of the most consistent findings with regard to health from anaerobic training include:
As we said before, your anaerobic energy systems provide the majority of the energy used to produce movement for maximum effort activity lasting ~1-4 minutes.
The sweet spot here is going to be in the ~1-2 minute range; as 2-4 minutes tends to be a 50/50 split between anaerobic and aerobic. [1]
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As you may have noticed: lifting weights oftentimes falls within this time frame as well.
It is true that lifting weights is going to be fueled primarily through anaerobic energy production.
The difference is that the energy production itself isn't the limiting factor in weightlifting.
In other words: when you hit failure on a set of 10 on leg press, the cause isn't necessarily anaerobic energy production itself.
In any training you do, whatever is the limiting factor to the exercise is what is being trained.
Thus, for maximum anaerobic development you will need something other than weight lifting alone.
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Exercise selections that will make the most sense include:
running
cycling
swimming
rowing
SkiErg
AirDyne (assault bike)
stairs
or anything similar
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There are a few different ways you can go about programming these exercises for anaerobic energy system development.
The simplest would be to approach it similarly to how you'd approach a set of squats.
In other words: when you do squats you are likely doing a set to near failure, resting for ~2-4 minutes, and then repeating this for however many sets you have planned for the day.
Taking that same approach, you could get on a Concept 2 Rower, row as fast as you can for 60 seconds, rest for ~2-4 minutes, and repeat for a planned number of sets.
This method is the easiest to combine with a strength training session, as you can simply treat this as one of your "lifts" for the day.
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Another tactic you can use is high intensity interval training (HIIT).
Understand though that most people have no idea what HIIT actually is.
It is not circuit training. It is not continuous high effort. It is an alternation between ridiculously high effort and ridiculously low effort. The low effort is crucial because without it you will never be able to achieve true high intensity due to fatigue.
On treadmill, you could do the following:
Run or walk at ~3-4/10 effort for 2 minutes
Run at ~9-10/10 effort for 2 minutes
Repeat 3-5x (depending on fitness level)
If you have access to a track, you could do:
1 lap at 3-4/10 effort
1 lap at 9-10/10 effort
Repeat 3–5x (again, depending on fitness level)
With this approach, the anaerobic training will likely be the entirety of the session. You could maybe toss some low-level accessory work on afterward, but you may find yourself not wanting to.
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It's worth noting that, when done right, this should be the hardest bit of training you do all week. By far.
1-2 sets using the first method I gave you will need ~48 hours for full recovery.
A full anaerobic session (as in the second method) will likely need ~72 hours for full recovery. [9]
With everything else that may be important for you to include in your training (lifting, endurance, etc.), this is probably most appropriately done just 1x/week.
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