CrossFit Conditioning: Build Endurance with Zone Training, a theoretical guide (part 1)
Introduction
In this 2-part blog series, conditioning/endurance training for CrossFit, building an engine. In this first part, I will break down some theory around training categorization and organization, as well as some practical testing options. Also we’ll discuss how to structure Crossfit conditioning workouts & how to match your engine-building training with Metcons. In the second blog, I will discuss the more practical application and actual training tools you can use to attack the individual qualities.
At its core, conditioning in CrossFit is all about work capacity, your ability to do a certain amount of work (reps, load, distance) within a specific timeframe. Actually, once you’ve mastered the skills and have a sufficient level of strength, work capacity is what separates CrossFit competitors.
Why CrossFit Conditioning Requires More Than Metcons
Originally, this work capacity was built through Metcons, the type of workout that became synonymous with CrossFit. By combining a bunch of movements and intensities in different time domains, you can get a novice to a very decent level of overall fitness. However, at some point this isn’t enough—not specific enough anymore—to make that next step, which is why they shouldn’t be your only form of conditioning if you’re a competitor.
Why? Because when training to improve conditioning, we aim to stress specific systems or limitations to those systems. These adaptations are often systemic, not local. We focus on the systems involved in uptake, delivery, and utilization of oxygen, which requires the global system to be stressed. However, in a Metcon that blends multiple stressors and potential limiters together, we often run the risk of having a muscle group or movement pattern break down before the energetic limitation is stressed enough.
Additionally, certain aerobic adaptations, more on that later, require lots of continuous volume and therefore typically a low, slow pace with lots of very small contractions. Which is hard to achieve with movements like squats, pull-ups, and burpees.
This is where monostructural training like rowing, biking, running, or skiing comes in. It’s low-impact, easy to pace, easy to measure, highly repeatable, and due to its low risk of local/CNS breakdown an effective tool to target specific energy systems.
That doesn’t mean ditch Metcons altogether. Instead, use them intentionally. They are the sport, so using them to practice and hone your skills is a must! Also, they are quite effective when used for high power output conditioning like short sprints, assuming enough volume can be accumulated. On top of that, they allow you to train and experience movements under fatigue, can be helpful to stimulate specific local adaptations. And of course, they are great fun, which in the end, is the reason we do the sport.
Lastly, it is good to mention that if programmed properly, Metcons can be used as a conditioning method. In that case, it’s important to aim for continuous movement and the appropriate RPEs, acquiring the required volume without unwanted bottlenecks. Especially movements that have relatively low contraction force and can therefore be done somewhat continuously—like sleds, carries, jumps, light squats or weightlifting movements—can be used to target more systemic adaptations. And, if used sparingly, they can even be combined with higher contraction movements, like high-skill gymnastics.
The 3-Zone Model of Conditioning: How it relates to “Zone 2” and Aerobic Threshold Training
Having a practical framework for understanding the different intensities of conditioning is a helpful way to fit conditioning requirements into a broader program. The 3-zone model is a simple model that allows you to break training into different intensity categories.
Zone 1: Low intensity, high volume. Think steady-state, conversational pace. Workouts in this zone are sustainable for long durations, think 45+ minutes. This is what’s classically and popularly called Zone 2 training, in a 5 zone model. Or Aerobic base training
Zone 2: Moderate intensity, moderate duration. This is the classic CrossFit grind. Workouts in this zone are sustainable for shorter timeframes, from 5 to 30 minutes. This often what’s referred to as anaerobic threshold training.
Zone 3: High intensity, short bursts. This zone includes sprint efforts and maximal intensity work—powerful but only sustainable for short periods, think 10 seconds to 2–3 minutes. This is often what’s referred to as high intensity training.
While most CrossFit workouts naturally fall into Zone 2, a balanced conditioning approach should include intentional time in all three zones. This helps you build a broad conditioning base focused on improving different aspects of your physiology.
Obviously, specific distribution of training within these zones is going to be different for each athlete and will change throughout the season. However, to give a rough estimation of the total training volume per zone for a competitive CrossFit athlete:
Zone 1: 60–75% of total training volume
Zone 2: 15–30% of total training volume
Zone 3: 10–20% of total training volume
The main point here is the imbalance between the amount of training done in Zone 1 versus Zones 2 & 3—which is quite different from what I usually see, where the majority of training is done in Zone 2.
Why Testing Matters: What is VO₂ Max, aerobic & anaerobic threshold and Why Does It Matter in CrossFit?
Thinking conceptually about the differences between these zones is a great step and can already be a major move toward breaking down and organizing conditioning efforts. However, to become more precise, it helps to look at and understand three major conditioning thresholds that help us understand an athlete’s physiology and prescribe training even better:
Aerobic Threshold: The line between Zone 1 and Zone 2. Often called Zone 2 in a 5-zone model. This threshold marks the highest power output one can sustain for longer periods of time (1 hour+). It is the power output at which the vast majority of energy is produced aerobically and little to no waste products accumulate.
Anaerobic Threshold: The line between Zone 2 and Zone 3. This is the highest power output one can sustain for around 20–60 minutes. At this point, anaerobic metabolism has become an important contributing part of energy production. When this threshold is crossed, we reach a point where work rates become unsustainable and waste products start accumulating so fast that breakdown and fatigue are unavoidable.
VO₂max: Although this is not a specific point in the model, it is a key metric. VO₂max is your aerobic ceiling, the highest rate at which your body can consume oxygen. It is an integrated metric that measures the capacity of your engine.
Knowing where these thresholds are gives you both accurate targets for training and insight into your power profile and physiological limiters, which can help you prioritize certain aspects.
The most precise measurements of these thresholds are done in a lab however, some simple field tests work great as a great starting point:
Aerobic Threshold: Nose-breathing step test
Bike or run 2:00–3:00 intervals, increase pace every round while nose-breathing. Start very easy. Stop the test when nose-breathing becomes difficult/labored. Pace/HR during the last full interval = Aerobic Threshold pace for that modality.
Anaerobic Threshold: 20-minute FTP-style test (on bike or rower)
20:00 all-out effort on the bike for max average wattage. Record average wattage and take 95% of it as estimated wattage @ anaerobic threshold. For power-dominant CrossFit athletes, 90–92.5% might be more accurate.
VO₂max estimation:
4:00 for max avg. wattage
Bike for 4:00 all-out and record avg. wattage to estimate VO₂max.
Step test:
Bike: Start at 100W and increase power by 25W every 2–3 minutes until failure, maintaining a cadence of 90–100 rpm. The highest fully completed stage is your estimated power at VO₂max. Aim for 6–10 rounds.
These give you repeatable, actionable data to guide your training. My preference is to do this on a stationary bike. It’s the most stable and repeatable testing environment in a CrossFit setting. Sessions are easy to replicate, and the bike provides consistent data like heart rate, wattage, RPE, and pace. That data allows for more precise training prescriptions down the line. It’s also low impact, making it easier to recover from and ideal for accumulating volume without breaking down the body. The technical demand is low, so athletes can focus purely on output without worrying about form or skill.
Running can work too, but it comes with more variables. It has a higher impact on the joints, making it harder to recover from. It’s also tougher to repeat in consistent conditions, and small differences in technique can have a big effect on pacing and efficiency, which skews test results.
How to Build Your Engine as a CrossFit Athlete
Using this knowledge and compressing it into training program that ultimately builds your engine is obviously what you need to do. Now this will involve carefully structuring your training volume and intensity distribution over the different zones, and doing regular (re)assessments.
In the next blog, I will discuss the practical application of these concepts and present a number of training examples. Click here to go to the next blog in this series.
Ready to level-up your engine? Let’s have a quick chat to explore how I can help you!
FAQ
How do I test my aerobic threshold for CrossFit?
A simple way to test your aerobic threshold is using a nose-breathing bike or running test, gradually increase pace until nasal breathing becomes difficult. That pace is your estimated aerobic threshold.
Is VO₂ max important for CrossFit athletes?
Yes. VO₂ max measures your body’s ability to use oxygen during intense exercise. A higher VO₂ max means better endurance and work capacity, crucial for competitive CrossFit.
Can I build conditioning in CrossFit without running?
Absolutely. Monostructural training like rowing, biking, or skiing, offers effective, low-impact ways to improve your conditioning without the joint stress of running.
Are Metcons enough for CrossFit conditioning?
Not entirely. While Metcons are great for general fitness, it is hard to target specific energy-systems without getting bottlenecked by movements. Targeting conditioning zones (1–3) isolated helps develop specific energy systems, which are essential for peak performance.