The ENDUROX Metabolic Calculator

At ENDUROX, we put science at the core of training. HYROX demands a unique balance between aerobic endurance and anaerobic power. Understanding where you sit on that spectrum is key to refining your preparation — and that’s where physiology comes in.
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Traditionally, this required expensive laboratory testing. But with the ENDUROX Metabolic Calculator, you can estimate the same key parameters — thresholds, training zones, substrate utilization, and metabolic profile — using simple field tests and data from your wearable.
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Why This Matters for HYROX

Mader & Heck’s classic model (1986) explained the “anaerobic threshold” as the point where the balance between lactate formation (from glycolysis) and lactate elimination (via oxidation) tips, causing net accumulation.

• VLamax → maximum lactate formation rate (glycolytic power).
• VO₂max → maximum oxidative capacity (aerobic engine).

The balance of these two determines your thresholds:

• High VLamax → more explosive capacity for sleds and wall balls, but lower thresholds and faster carbohydrate reliance.
• Low VLamax → greater endurance and substrate efficiency, but reduced peak power for strength/power based exercise stations.

In HYROX, this trade-off is critical: you need enough glycolytic capacity to handle the stations, but not so much that your running economy collapses.
The calculator uses your VO₂max and VLamax to predict:

• Lactate Thresholds (LTP1 & LTP2) → to set ENDUROX training zones.
• Substrate utilization profile → showing how your body shifts between fat and carbohydrate use at different intensities.

The really cool thing is, you can also visually see how anaerobic power effect your thresholds.

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How to Estimate VLamax

You can choose between a running or cycling protocol. Running is great if you are confident sprinting at full speed, but for many, cycling is a safer alternative.

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Running Protocol (HYROX-specific)

1. Take a resting blood lactate sample.
2. Warm up with 10–15 min of easy running plus strides.
3. Perform a 15-second all-out sprint.
4. Take lactate samples immediately after, then at 1 and 3 min, and every 2 min until past the peak.
5. Cool down.

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Cycling Protocol

1. Take a resting lactate sample.
2. Warm up for 10–15 min, finishing with 2–3 short sprints.
3. Perform a 15-second all-out sprint on a stationary bike.
4. Take lactate samples immediately after, then at 1 and 3 min, and every 2 min until past the peak.
5. Cool down.

👉 Enter these values into the VLamax area of the ENDUROX Calculator as seen below:

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Why 15 Seconds?

Mader & Heck showed that short maximal work allows you to approximate maximum glycolytic rate (dLa/dt max) — essentially the ceiling of lactate production. Measuring how high and how quickly lactate rises after such an effort reflects your glycolytic (anaerobic) capacity.

If you don’t have access to a lactate meter, you can use an estimation. Here’s a guide to interpreting VLamax values:

• Very Low (≤ 0.2): Elite Ironman triathletes, pro cyclists, ultra-endurance athletes. Suppressed glycolytic activity, excellent oxidative metabolism.
• Low (0.2 – 0.4): Trained endurance athletes (e.g., marathoners, long-course triathletes). Balanced thresholds and efficiency.
• Moderate (0.4 – 0.6): “All-rounder” range, good aerobic and anaerobic performance.
• High (0.6 – 0.8): Middle-distance runners, rowers, CrossFit athletes. Strong anaerobic power, less endurance efficiency.
• Very High (≥ 0.8): Sprinters, track cyclists, power athletes. Exceptional anaerobic burst, poor economy for endurance.

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What’s the Ideal VLamax for HYROX?

For HYROX, the aim is to keep VLamax relatively low, as this raises your running thresholds and allows you to sustain higher speeds across the 8 km of running — arguably one of the biggest determinants of overall success.

However, you don’t want VLamax to fall too far. If it drops too low, you lose the explosive glycolytic power needed for stations like the sled push and pull, burpee broad jumps, lunges, and wall balls. It's a fine balance!

The ideal balance is a VLamax low enough to boost endurance, but not so suppressed that you can’t generate the power required for heavy, high-intensity work. Exactly where that sweet spot lies isn’t known — it’s a fascinating area for future research in HYROX physiology — but an educated guess might be:

• > 0.6 is too high
• < 0.3 is too low

This may also explain why we don’t see much crossover success from super-elite CrossFit athletes (who push VLamax very high) or Ironman triathletes (who drive it very low). Those extremes make them exceptional in their own sports, but less suited to HYROX’s hybrid demands.

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How to Estimate VO₂max

Of course, getting into a lab and directly assessing both VO₂max and maximum aerobic velocity (MAV or vVO₂max) is best. But if that’s not possible, here is another solution:

• 1: Use your wearable’s VO₂max estimate (Garmin and similar devices ok).
• 2: Estimate MAV (vVO₂max) from VO₂max.

MAV reflects both your VO₂max and your running economy. This means:

• Highly economical runners may see MAV slightly underestimated.
• Less economical runners may see MAV slightly overestimated.

It’s not perfect, but it’s close enough to be useful for training.

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How the Calculator Works

Mader & Heck’s model describes the “crossing point” where glycolytic lactate production outpaces mitochondrial clearance. This defines your upper lactate threshold (LTP2).

• Below LTP2: Substrate use is balanced between fat and carbohydrate.
• Above LTP2: Reliance shifts heavily toward carbohydrate, and lactate accumulates.

By combining VO₂max and VLamax, the calculator predicts:

• Your thresholds → the intensities that separate sustainable from fatiguing work.
• How your anaerobic capacity effects and shifts your running thresholds.

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Putting It Into Practice

Once you’ve entered your VO₂max and VLamax:

• You’ll know which zones to train when building aerobic capacity.
• You’ll see how much glycolytic power you carry into sleds and wall balls.
• You’ll understand whether your physiology is more “runner” or “power athlete” — and how to rebalance it for peak HYROX performance.

🎯 Access the ENDUROX Metabolic Calculator

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Train With the ENDUROX Society

At ENDUROX, we don’t just stop at the science. We build these principles directly into our training plans — so you’re not only learning your physiology, but also applying it every week.

💥 Train with us and join the ENDUROX Society — our global community of athletes and coaches committed to building world-class HYROX performance through science-backed training. Check it out here.

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