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Mastering Training Zones with Critical Speed

Mastering training zones

Maximising performance in HYROX and running demands a smart approach to training, and that’s where understanding training zones becomes crucial. However, accurately identifying these zones is often a challenge, particularly without specialised lactate threshold and VO2Max testing. In this focused guide, we'll explore how HYROX athletes and runners can effectively use the concept of 'Critical Speed' to define their training zones, bypassing the need for expensive lab tests. This approach simplifies training by using a practical and scientifically-backed method to align workouts with your performance goals, ensuring every session is as efficient and productive as possible

The Importance of Training Zones For HYROX


Understanding Training Zones:

Training zones are defined ranges of exercise intensity, typically based on speed, power output, or heart rate. Each zone represents a different level of effort, from very light to very hard, and is linked to specific physiological responses and training benefits. Lower zones focus on building endurance and aerobic capacity, while higher zones are aimed at improving speed, power, and anaerobic capacity.

Their Importance for Runners and HYROX Athletes:

For runners and HYROX athletes, these zones are essential. They provide a framework to structure workouts effectively, ensuring you're training at the optimal intensity for your fitness goals. Properly applied, these zones help build endurance, enhance speed, and raise your anaerobic threshold. This is especially crucial in HYROX, where understanding the intensity of your race and training accordingly can make a significant difference in your performance.

Optimising Performance Through Training Zones:

Training within these zones allows you to tailor your workouts to your current fitness level and specific goals. Training in higher intensity zones, for instance, boosts your lactate threshold – key for both endurance sports and HYROX, enabling you to maintain faster paces for longer without fatigue. Conversely, lower intensity zones aid in recovery and the development of a robust aerobic base. The essence of effective training lies in striking a balance across these zones, combining rigorous workouts with sufficient recovery and aerobic conditioning.

Keeping things simple with a 3 Zone Model

Understanding the nuances of training zones doesn't have to be a complex endeavour. In fact, simplifying this approach can often lead to more focused and effective training. This is where the concept of a three-zone model comes into play. By distilling the intensity spectrum into three broad zones, we can streamline the training process, making it more accessible and manageable, especially for runners and HYROX athletes. This model effectively captures the essential training intensities while eliminating the complexity of more granular systems. In the following section, we'll explore how this three-zone model operates and why it might be the most beneficial approach for your training regimen, striking the perfect balance between simplicity and precision in training zone allocation.

3 Zone Model for HYROX

Zone 1: Aerobic Endurance Zone (Zone 1 & 2 in a 5 zone model)

  • Intensity: This zone corresponds to low-intensity efforts, typically under 70-75% of maximum heart rate (MHR) or below the first lactate threshold (LT1).

  • Purpose: Training in this zone develops basic endurance and aerobic capacity. It’s characterised by longer durations of exercise where you can comfortably talk without much strain.

  • Benefits: Improves fat burning, enhances blood circulation, strengthens the heart, and builds an aerobic base without causing significant fatigue.

Zone 2: Threshold Zone (Zone 3 and 4 in a 5 zone model_

  • Intensity: This is a moderate to high-intensity zone, ranging from 75-85% of MHR, situated around the second lactate threshold (LT2) or the anaerobic threshold.

  • Purpose: Training in this zone focuses on improving your ability to sustain a higher intensity for longer periods. It's where you start to feel a significant but sustainable effort, and conversation becomes more challenging.

  • Benefits: Increases the body’s ability to clear lactate, improves efficiency, and raises the intensity at which the body can perform without quickly going into anaerobic metabolism.

Zone 3: High-Intensity Zone (Zone 5 in a 5 Zone model)

  • Intensity: This is a high to very high-intensity zone, typically above 85% of MHR, where you are pushing close to or at your maximum effort.

  • Purpose: Training in this zone is about short, intense bursts that improve speed, power, and anaerobic capacity. Efforts in this zone are unsustainable for long periods.

  • Benefits: Enhances the body's ability to handle high-intensity efforts, improves anaerobic energy systems, and increases maximum power output.

Why the Three-Zone Model Is Beneficial:

  • Simplicity: It’s easier to understand and implement, especially for athletes without extensive knowledge in exercise physiology.

  • Covers Key Aspects of Training: Despite its simplicity, it effectively addresses the major areas of endurance training – from building a strong aerobic foundation to enhancing high-intensity performance capabilities.

  • Adaptability: Suitable for a wide range of endurance sports, including running and HYROX, it can be easily adapted to different training needs and goals.


Setting Training Zones using either Lactate or Critical Speed

Understanding how to accurately set your training zones is crucial for tailoring your workouts effectively. Depending on the equipment you have access to, there are a couple of primary methods you can use: lactate threshold and critical power or speed. Let's explore these in more detail:


Lactate Threshold Testing

The most precise way to establish your training zones is through lactate threshold testing, typically conducted in a specialised setting. This method involves a graded exercise test, where the intensity incrementally increases, and blood lactate concentrations are monitored. As the intensity rises, so does the blood lactate level, and this relationship is used to identify lactate thresholds. This type of testing can be adapted for various endurance sports like running, cycling, rowing, and even swimming using portable lactate analysers.

Lactate Testing


The test helps in identifying two key lactate thresholds:


  1. LT1 (Aerobic Threshold): This marks the boundary between Zone 1 and Zone 2 in a 3 zone model or 1 and 2 in a 3 zone model. LT1 is identified as the point where there's a sustained increase in blood lactate concentration above resting values. It signifies the shift from primarily aerobic metabolism to a mix where lactate begins to accumulate.

  2. LT2 (Lactate Threshold  2 or MLSS): This separates Zone 2 and Zone 3 in a 3 zone model and 4 and 5 in a 5 zone model. See it as the tipping point before entering the red zone. LT2 is recognised as the intensity that triggers a rapid increase in blood lactate, indicating the upper limit of equilibrium between lactate production and clearance.


Example: Consider a runners lactate threshold test results, which can be visually represented with the 3-zone model overlaid. This graphically illustrates where their LT1 and LT2 fall, helping to define their training zones with precision.

HYROX 3 zone model


Critical Power or Speed

 Another method, particularly useful when lab testing isn’t an option, is to determine your critical power (for cyclists) or critical speed (for runners). This involves field tests where you perform maximal efforts over different distances or durations. The data from these efforts can then be analysed to estimate the power or speed at which you transition from aerobic to anaerobic metabolism, which can be used to set your training zones.

Critical speed for hyrox

Critical Speed: An Effective Measure for Runners and HYROX Athletes

Not every sport allows for precise power measurement, making critical speed a valuable metric for many endurance athletes, especially runners. This concept operates similarly to critical power, offering a tangible physiological marker to distinguish between Zone 2 and Zone 3 training intensities. 

Determining Your Critical Speed: To establish your critical speed, you'll need to perform two time trials: one that's roughly 3 minutes long and another around 12 minutes. These could be actual race times or dedicated trials. Here's a simple protocol you might follow:


  1. Warm-Up Thoroughly: Start with a comprehensive warm-up to get your body ready for maximal effort.

  2. 1200m Time Trial: Run a 1200m time trial as fast as you can and note the time it takes to complete. Ideally you want to be able to do this somewhere flat.

  3. Rest: Take a 30-minute break to fully recover before the next effort.

  4. 3600m Time Trial: Similar to the first, run a 3600m time trial and record the time.


After you've completed these trials, you can calculate your critical speed using the distances and durations from your efforts. Use our free tool here by clicking here.

critical speed calculator


Interpreting Critical Speed and LT1

While we can’t know your LT1 for sure from Critical Speed, we can estimate it to be around 70-75%. For instance, if your critical speed is 15 km/hr,  approximately 11 km/hr. This estimate can be incredibly useful for setting the lower end of your training zones. However, the only real way to know your LT1 is through lactate testing.

While the concept of critical speed is invaluable for tailoring training intensities, it does present a limitation in accurately estimating the first lactate threshold (LT1). Critical speed primarily helps identify the higher end of an athlete's endurance capacity, but pinning down LT1 – the point at which lactate begins to accumulate more significantly in the blood – often requires a degree of estimation. This means that while we can effectively use critical speed to inform higher-intensity training zones, identifying the lower boundary of moderate-intensity efforts (LT1) is not as precise and typically relies on educated guesses or additional testing methods.


Are you ready to take your training to the next level? Here’s how you can get started:


Get Your Lactate Test: Uncover the precise data of your lactate thresholds in a lab setting. This will give you the most accurate insight into your training zones.


Combine with Critical Speed Test: Complement your lactate test with a critical speed test. This combination will provide a comprehensive overview of your endurance capabilities.


Tailored Running Programming: Looking for a customised training plan? Get in touch at with us for personalised running programming that caters to your unique needs and goals.




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