Conditioning in CrossFit: Building an epic Engine (part 2)
In the first post, I broke down the theory—how to categorize different types of conditioning using a simple 3-zone model, how to think about training organization, and how to assess key thresholds like aerobic and anaerobic capacity. Now it’s time to shift gears.
In this second part, I’ll focus on the practical application: how to actually improve conditioning for CrossFit. I’ll discuss how to build an aerobic base, improve your anaerobic threshold, and push your VO₂max. Whether you’re trying to recover faster, hang on longer in tough Metcons, or compete at a higher level, this post will give you actionable strategies to build a better engine.
The Power of Aerobic Base Training
If there’s one thing that pays off over time, it’s a strong aerobic base. To quickly recap, I define the aerobic base by the aerobic threshold, which is the highest sustainable output you can achieve before your anaerobic system kicks into the next gear. Aerobic Zone 1 runs exactly up to the aerobic threshold, separating Zone 1 and 2. Improving your aerobic base means improving your body’s ability to deliver oxygen to the working muscles. This means:
Increased work capacity of the muscle due to improved oxygen delivery
Better recovery between rounds and sessions, due to faster clearance and quicker replenishment
Higher sustainable power output, due to a higher threshold
Traditionally, this is built with long, steady work—nasal-breathing efforts popularly called “Zone 2,” which, in our 3-zone model, is actually Zone 1. For athletes already training hard multiple times a week, this low-fatigue option is likely the best choice.
However, the adaptations you get from long steady work aren’t unique to that type of training. What drives adaptation is the product of intensity × time, and higher intensities bring more adaptations per unit of time. But here’s the issue:
For significant adaptations to occur, a relatively large training dose needs to be accumulated.
Higher intensities come with exponentially increasing fatigue and recovery costs.
This explains why, for people already training close to their limits due to the amount of high-intensity CrossFit, accumulating the required volume at high intensity is not an option. However, those who are not yet close to their recoverable volume might be better off increasing the intensity of their overall training load to increase training results—especially if they don’t have the option of doing more total training.
This is why, for the average class member training 2–3x a week, high-intensity CrossFit-style training is likely the most optimal. So:
If you’re training 4–5x/week: Use low-intensity aerobic work to keep progressing without burning out.
If you’re only training 2–3x/week: Moderate-to-high-intensity sessions likely give you more bang for your buck.
Practical training example (monostructural):
45+ minutes of biking at or around the aerobic threshold
Practical training example (mixed-modal):
AMRAP 45:
500m row
50m sled push (RPE 6–7)
10 deadlifts @ 40% 1RM
100m KB carry
20 air squats
How to prescribe pacing:
RPE 5–6
+/- 75% of FTP score
Highest pace while comfortably nose breathing
60–70% of max heart rate
Sustainable rounds/intervals
Anaerobic Threshold: Where CrossFit Happens
Your anaerobic threshold is your redline—the highest sustainable pace before fatigue kicks in hard, due to increasing dependence on anaerobic metabolism. Think: CrossFit Open-style efforts. The threshold is the separation between Zone 2 and 3, and Zone 2 is what is called the anaerobic zone.
The majority of CrossFit work is done here, so even though it’s an important threshold to train and push, most competitive athletes probably need to back off from this type of training. Additionally, in some cases, this threshold is actually most effectively raised by improving maximal power output, VO₂max, or one’s aerobic base—not by pushing the actual threshold. But more on that some other time.
For this article, I’ll focus on direct targeting of the anaerobic threshold. Improving the anaerobic threshold means improving the highest sustainable power output. One’s pace and durability at the anaerobic threshold are arguably the most important aspects of the engine. Improving the anaerobic threshold means improving your race speed or capacity to operate at race speed for longer times.
To train it directly, you want to train at or around the threshold, push close to the limit, but still make sure you keep the efforts sustainable:
Do 4–8 minute intervals at 80–90% effort
Rest equally or slightly less than the work
Keep the pacing steady and sustainable
Example sessions:
Monostructural:
4–6 rounds
4:00 on bike @ RPE 7–8
2:00–4:00 recovery spin
Mixed-modal:
4–6 x AMRAP 4:
50 double unders
10 burpees
10 thrusters (light)
Max row calories @ RPE 8
Goal = consistent performance across rounds, not all-out efforts.
Building Your VO₂max the Smart Way
VO₂max is your aerobic ceiling—the highest rate at which your body can consume oxygen, which is the result of your body’s ability to uptake, transport, deliver, and use oxygen. For athletes new to conditioning training, raising your VO₂max raises every threshold below it.
Additionally, with more experienced athletes, we also see that when one’s anaerobic threshold is relatively close to one’s VO₂max, raising one’s VO₂max is a necessary step to push the anaerobic threshold higher. Just as with the anaerobic threshold, in later stages of training, pushing VO₂max up sometimes requires training of other qualities first.
Early on, simple protocols like 40/20 intervals or short AMRAPs deliver strong results. But as you advance, so should your training. VO₂max isn't one-dimensional—it’s the sum of:
Oxygen uptake → Train your lungs
Oxygen transport → Train your heart and blood flow
Oxygen utilization → Train your muscle endurance
Looking at the direct interventions targeting VO₂max:
Example sessions:
3 rounds for time of:
6 x 40 seconds max effort / 20 seconds rest Echo Bike
Rest 6:00 between rounds
3 x AMRAP 5:
2 rounds of:
15 thrusters (unbroken)
15 burpee box jump overs
Max calories on rower in remaining time
Rest 5:00 between AMRAPs
In Summary: Train Smart, Not Just Hard
CrossFit conditioning isn’t just about surviving Metcons and pushing hard. Once you become more advanced, developing your engine needs to be done with strategy and purpose. Use zone-based training to balance intensity and volume. Test your thresholds to track progress. Mix in targeted monostructural work to build capacity without burnout.
Conditioning isn’t guesswork—it’s training with intention.