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Why the same VO₂max can lead to different 5 km results

Maximum oxygen uptake is one part of your performance profile. The cost of running, sustainable effort and fatigue also matter.

ALEXANDER SELEZNEV · ENGLISH EDITION · 28 SEPTEMBER 2026

Running and training with Alexander Seleznev

One number does not describe the whole runner

Two runners can have the same VO₂max and reach very different speeds. The coaching question is how much speed each runner produces with that oxygen supply, how long it can be sustained, and what changes with fatigue. A watch estimate and a laboratory gas-exchange measurement should not be treated as interchangeable. Small changes also need to be considered against measurement variability.

Oxygen transport and utilisation

Muscle contraction requires continuous ATP resynthesis. In oxidative metabolism, oxygen is the final electron acceptor in the respiratory chain. It must be transported to the muscles and used in the mitochondria. The Fick principle expresses whole-body oxygen uptake as cardiac output multiplied by the arterial–venous oxygen content difference. The same VO₂max can therefore arise from different combinations of delivery and extraction; it does not identify a runner’s limiting factor by itself.

The oxygen cost of speed

Running economy describes the cost of running at a given speed. Oxygen cost and energy cost are related, but their relationship depends on the fuels being oxidised. Muscle work, elastic tissue behaviour, coordination, footwear and the surface can all contribute. A visually elegant stride is not proof of good economy.

A worked example, not a race prediction

Take the illustrative model q = 5 + k × v, where q is oxygen uptake in ml/kg/min and v is speed in m/min. At q = 65, k = 0.20 gives 300 m/min (18 km/h); k = 0.22 gives about 272.7 m/min (16.36 km/h). These invented values demonstrate the arithmetic. They are neither athlete results nor an interval prescription.

What the 5 km adds

Race performance also depends on threshold characteristics, oxygen uptake kinetics, the ability to work above a sustainable intensity, pacing and fatigue resistance. Oxidative metabolism contributes from the start, while phosphocreatine and glycolysis help meet rapid changes in ATP demand. No single percentage of VO₂max gives every runner the same race effort.

How this changes coaching

Begin with results and training context, form a testable hypothesis, and repeat a comparable assessment after a training block. Improvement without an increase in VO₂max can still be meaningful progress. Research linking VO₂max and economy to 16 km performance supports considering them together, but does not provide a universal 5 km calculator.