Build you perfect "Endurance House"
To understand Training Zones is not enough. What you need is to understand how your “Endurance House” looks and what kind of “renovation” it needs to become a better long distance runner.
7 min read


Let’s first go through training zones and then look at the ideal “Endurance House” we want to have. Using the 5 training zones model, we can create a solid analogy to understand how each zone contributes to your running performance.
1️⃣ The Foundation – Zone 1
This is the base of your house and represents low-effort activity, where lactate levels are very low (ideally around 1 mmol/l). Several crucial physiological adaptations happen here:
Maximal Fat Oxidation: At this intensity, your body primarily uses fat for fuel, training your fat metabolism. The more time you spend in Zone 1, the more efficient your fat-fueling becomes, saving precious carbs for higher intensities. For example, a beginner might burn just 1-2 kcal of fat per minute in Zone 1, while a well-trained runner can burn up to 7 kcal per minute.
Low-intensity training builds a capillary network in your muscles, improving oxygen delivery to working muscles.
Zone 1 activity increases both the number and size of mitochondria, essential for energy production, lactate reuse, and waste elimination during high-intensity exercise.
It boosts the production of proteins and enzymes involved in aerobic energy production.
Zone 1 helps flush out waste products and promotes recovery after hard sessions.
2️⃣ The First Floor – Zone 2
Zone 2 builds on the foundation. Many of the processes from Zone 1 still occur here, but at a slightly reduced rate. The fat-to-carb fuel ratio also shifts toward more carb use. In Zone 2, lactate remains below 2 mmol/l, and the "ceiling" of this floor marks the Aerobic Threshold (LT1). Zone 2 plays a crucial role in building aerobic endurance and capacity. It is often referred to as the "sweet spot" for endurance training because it offers a balance between volume and intensity.
Zone 2 helps raise your aerobic threshold (LT1)—the point where fat and carbohydrates are utilized almost equally for energy. This means you can sustain higher intensities without relying heavily on glycogen stores.
Training in Zone 2 promotes mitochondrial growth and function, allowing your muscles to use oxygen more efficiently for energy production.
While less pronounced than in Zone 1, Zone 2 still supports the development of capillaries, improving oxygen delivery to muscles.
Although carbohydrate reliance increases compared to Zone 1, Zone 2 still trains your body to utilize fat as a fuel source effectively. This is particularly important for endurance athletes aiming to conserve glycogen for later stages of long races.
3️⃣ The Second Floor – Zone 3
The second floor begins at the Aerobic Threshold (LT1), where fat and carbs are used in roughly equal amounts for fuel. This is the point where intensity shifts from easy/moderate to moderate/effort.
Zone 3 works just above your aerobic threshold (LT1), where carbohydrate utilization starts to dominate over fat metabolism.
Blood lactate begins to accumulate, but your body can still clear it effectively.
Fatigue starts to build up subtly, even if the effort feels manageable.
Training at this level requires recovery, even if it doesn’t feel as taxing as higher intensities.
4️⃣ The Ceiling of the Second Floor – Zone 4 – Lactate Threshold 2 (LT2)
This is the Lactate Threshold 2, where the work gets hard:
Carbs/glycogen become the primary fuel source.
The aerobic system is still highly active and provides a significant portion of the energy. The anaerobic system starts contributing more because the energy demand exceeds what the aerobic system can supply alone.
Oxygen is delivered to the muscles at near-maximal capacity, but it’s not sufficient to meet the entire energy demand, so anaerobic metabolism fills the gap.
The body is still able to clear lactate efficiently, but the rate of production and clearance are nearly balanced. Hydrogen ions (H+) associated with lactate production start to accumulate, causing muscle fatigue and a burning sensation.
Zone 4 is a "threshold zone," meaning you can sustain this effort for a limited time, typically 30-60 minutes for trained individuals.
In theory, lactate levels rise to 4 mmol/l at LT2, but individual differences can only be accurately measured in a lab.
5️⃣ The Roof – Zone 5 – VO2max
In fact VO2max (maximal oxygen uptake) is at the top of the roof. It is a kind of limit above which you can’t jump. At least at the current fitness level. Zone 5 is a very hard effort lasting normally less than 2 minutes:
Oxygen demand exceeds supply, and energy production relies heavily on anaerobic processes.
Lactate levels can soar as high as 12-14 mmol/l for some individuals. because the rate of lactate accumulation exceeds the body's ability to clear it.
Increased blood acidity, primarily due to the dissociation of hydrogen ions (H+) associated with lactate production, not lactate itself.


This is a theory. Now a few practical points. What kind of a house do we want to have as long distance runners?
Well, it may not be the most beautiful structure, but it’s built for function.
We aim to create a strong foundation, focusing on metabolic efficiency and the ability to use fat as the primary fuel source on easy and moderate sessions. This makes us more aerobically efficient. By improving fat utilization, we tap into an almost endless energy reserve, allowing us to run faster over time. For instance, with consistent Zone 1 training over a year, you might progress from running 7 min/km to 6 min/km on easy runs. However, building this foundation takes time and patience - something many runners struggle with as they chase quick personal bests, often opting for shortcuts.
Incorporating workouts that balance between the first and second floors (Zone 2-3) helps develop the first Lactate Threshold (aerobic threshold). I recommend doing most long runs in this range, with some variations. This is especially crucial for marathon runners. The goal is to bring the aerobic threshold (LT1) closer to the anaerobic threshold (LT2). This allows us to use more fat than carbs at higher paces, reducing lactate buildup and enabling us to run faster for longer with less energy expenditure. You can do a lot of fun sessions: fartleks and alternating paces long runs. To imagine this session in our house you simply run back and forth from the first floor to the second floor and back. As many times as needed.
We also strive for a relatively "flat roof," where the second Lactate Threshold (anaerobic threshold) is closer to VO2max. This helps us sustain a fast pace for a longer duration, even as fatigue sets in.


What If You’re a Newbie or Running Without Structure? For many runners, the house might look unstable:
No solid foundation, or with just a small one, progress is more difficult. Those with a sports background are in a better position because their "house" is built on solid, quality ground, making it easier to improve. On the other hand, those who haven’t been active in sports often have their house placed in a swampy area, requiring extra effort to first build a strong foundation. If they don’t, the whole structure could collapse over time.
The first floor of their house is also quite small. What many runners do is jump straight to the second floor, which seems easier, right? They enjoy the space up there and sometimes even run up to the roof - it is so much fun! But they neglect the important work of strengthening the foundation and building up the first floor.
Indeed, this shortcut approach can lead to short-term improvements. Some runners, especially those with a bit more strength, may perform well for a few years. However, injuries, overtraining, or burnout will eventually catch up with them.
We must also consider individual differences—sports background, age, genetics, body composition, and health conditions. Everyone has their own unique house. That’s why training must be personalized. Some may need to focus on raising the roof first, while others might do well building up the floors without touching the roof. Regardless of the approach, the foundation is always key. If it's weak, whatever you build on top can collapse at any moment.
It's also important to remember that the boundaries between training zones are not fixed. They are fluid. We often start running in one zone and finish in another. There are many nuances to consider in training, too.
Many runners feel disappointed when they take a running test and discover that their thresholds are lower than they expected. Some labs, however, fail to deliver accurate results. For instance, they might measure lactate levels at 2 mmol/L and 4 mmol/L (theoretical thresholds) but don't take the time to determine the individual thresholds (real thresholds). And then there’s the myth that "you don’t train anything when you run below the aerobic threshold." That’s simply not true.
I appreciate having laboratory data with lactate values, but I’m also comfortable working with the estimations from tools like intervals.icu. Often, I manually adjust these values when necessary, and it works well.
Key Takeaways for Training
1️⃣ Spend Time in Zone 1 and Zone 2
For beginners and slower runners, Zone 1 might involve walking, hiking, or cycling to build aerobic capacity. Without a solid foundation, running at this intensity will be very slow and can feel mentally challenging.
Over time, as your fitness improves, what was once Zone 2 may shift to Zone 1. This allows for more flexibility with easy paces: use Zone 1 when you feel tired and need recovery, and Zone 2 for building basic mileage.
2️⃣ Balance Intensities
Tailor your training to your goals and individual responses. The 80/20 rule (80% low-intensity, 20% higher-intensity) works well for most runners, but it doesn’t have to apply rigidly to every week. Instead, think of it as a guideline over the course of a year.
Your distance goals, mileage, number of sessions, and races will all affect this balance. When you incorporate more intensity into your training, be sure to follow it up with plenty of easy miles to rebuild your foundation.
3️⃣ Be Flexible
Listen to your body. Life stress, fatigue, and other factors can influence your training. Treat your training plan as a guideline, not a strict rulebook. Adjust as needed to stay consistent and avoid burnout.
4️⃣ Lab Testing vs. Estimations
Lab tests can provide valuable data but aren’t always necessary. Tools like intervals.icu or similar platforms offer reliable estimations, which can be fine-tuned based on your performance and feedback.
Training is like building a house: a strong foundation supports everything above it. With patience, consistency, and a personalized approach, you can create a sturdy, efficient "house" to sustain your running goals for years to come. Patience and discipline are your greatest allies in this journey.