How Fast Should You Run During A Running-Economy Test?

Back to that beer study for a moment. The researchers measured running economy at 8 km/h. That’s a perfectly concrete question—how much oxygen does it cost you to hold this speed? But if you’re a collegiate runner trying to shave seconds off your 5K, you might reasonably want to know what happens a little closer to race pace.

Thirteen NCAA Division I women’s cross-country runners completed five-minute treadmill bouts at 70%, 80%, 90%, and 100% of their individual 5K race speed. Oxygen use at all three slower speeds tracked closely with oxygen use at race speed. If oxygen was all you measured, any of the three would look pretty informative.¹O’Neal, E. K., Knight, S. N., Bowling, L. R., Scudamore, E. M., Scudamore, V., & Waldman, H. S. (2026). Running economy assessment at 90% of 5-km pace is more informative than lower intensities among women’s NCAA division I cross-country competitors. Journal of Strength and Conditioning Research, 10.1519/JSC.0000000000005708. PubMed. https://doi.org/10.1519/JSC.0000000000005708

The difference showed up in the runners’ breath. The researchers also measured respiratory exchange ratio (RER), the amount of carbon dioxide you breathe out relative to the oxygen you consume. During steady running, that ratio helps researchers estimate how much energy you’re using. Run hard enough and extra carbon dioxide from buffering acid makes the calculation harder to interpret.

Only at 90% of 5K speed did runners’ RER values track significantly with their race-speed values. And at 90%, every runner still had an RER of 0.99 or lower, allowing the researchers to estimate energy cost. For these women, that speed gave the lab a closer look at race metabolism while keeping the calculation usable.

What this means for runners

If you’re getting an economy test to see whether a training block has made you more efficient at 5K intensity, ask the lab how it chose the treadmill speed. An easy jog can tell you whether that jog has become cheaper. A faster stage may give you a better read on the effort you care about racing.

One practical detail if you’re doing the math at home. For a 20-minute 5K runner, 90% of race speed works out to about 4:27 per kilometer, compared with 4:00 per kilometer on race day. That’s an example of a test speed. The researchers studied how to measure economy in 13 collegiate women. Finding the best workout to improve it is a different experiment.

References

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  O’Neal, E. K., Knight, S. N., Bowling, L. R., Scudamore, E. M., Scudamore, V., & Waldman, H. S. (2026). Running economy assessment at 90% of 5-km pace is more informative than lower intensities among women’s NCAA division I cross-country competitors. Journal of Strength and Conditioning Research, 10.1519/JSC.0000000000005708. PubMed. https://doi.org/10.1519/JSC.0000000000005708 ↩︎