How Accurate Is Lactate Threshold Testing for Marathon Performance?

Why Marathon Predictions Are Usually Inaccurate

Most marathon pacing strategies are based on:

• Recent 5k or 10k race times

• Online calculators

• Generic heart rate zones

The problem is these methods assume everyone has the same physiological profile. They don’t.

For example: Two athletes can both run the same 5km time, but one may have a high VO2max with low lactate threshold, while another may have a lower VO2max but exceptional lactate threshold. How they perform over a marathon will differ and moreover, how they might structure their training could be personalised too. 

Without measuring LT1 and LT2 directly, you are guessing.

Estimates based on short tests:

• Are mathematical assumptions

• Conflate physiology and psychology

• Don’t identify LT1 or LT2 (true metabolic thresholds)

• Can misrepresent long-distance sustainability. For marathon performance, that’s dangerous.

What We Actually Measured

For this athlete, we performed:

• 3 minute incremental step test to determine lactate thresholds
• Subsequent VO2max testing consisting of 1 minute incremental stages to failure

This allowed us to identify:

• LT1 (aerobic stability point)

• LT2 (upper sustainable metabolic threshold)

Research (Smyth et al., 2020, Med Sci Sports Exercise) shows a strong relationship between critical speed relative to marathon speed and finish time. Slower runners tended to race at a lower percentage of their critical speed (which is not too far from LT2). Faster runners were able to run at a much higher percentage of LT2.

We applied this evidence-based model.

The Prediction

Based on his LT2, training history and current fitness we suggested that the athlete could sustain between 85-90% of his LT2:

85% of LT2 → 2:54:55 (4:08/km pace)

90% of LT2 → 2:45:20 (3:55/km pace)

Projected competitive window: ~2:46–2:55

Actual Seville 2026 finish time: 2:47:59

That sits directly within the predicted physiological range and the athletes pacing was consistent over 42.2km.

This wasn’t a guess. It was anchored to measurable metabolic data.

Why This Works

Marathon performance is largely governed by:

• Fractional utilisation (how close you can race to LT2)

• Durability

• Glycogen depletion and carbohydrate intake

• Lactate production vs clearance balance

As shown in the research and outlined in our endurance framework:

• VO2max alone is not enough

• Estimates dont identify personal metabolic thresholds

• Threshold running speed changes differently to VO2max with training

• Marathon pacing must preserve metabolic stability

Marathon racing sits in a narrow metabolic band.

If you don’t know your band, you’re gambling.

What This Means for Runners

Lactate testing allows you to:

• Train at true physiological zones

• Anchor long runs correctly

• Avoid overestimating sustainable pace

• Fuel based on substrate utilisation

• Race without guesswork

For serious endurance athletes, this removes ambiguity.

You’re not chasing arbitrary pace. You’re training the system.

Who This Is For

• Marathon runners

• Competitive age group triathletes

• Long-course endurance athletes

• Coaches wanting precise athlete profiling

If you’re preparing for a marathon and want clarity on:

• Your true sustainable race pace

• Where your lactate thresholds sit

• Whether you’re limited by VO2max or fractional utilisation

• How to fuel correctly

Book a VO2max & Lactate Threshold Test at The Edge.

Replace guesswork with measurable physiology.