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3d ago

Yearlong Tracking Finds Metabolic Ceiling for Elite Endurance at About 2.5× BMR

Isotope-based measurements in 14 top athletes indicate a duration-dependent cap on sustainable energy use.

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Endurance in the long haul: over weeks to months, daily energy burn trends toward a common ceiling— even for elites. (Credit: Louis Dty on Shutterstock)
United States ultramarathon runner Courtney Dauwalter runs through the mountains near Twin Lakes, Colorado. Dauwalter sits at the apex of an elite group of ultra runners–people who run 50, 100 or 200 miles–in one go.
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Overview

  • Published October 20 in Current Biology, the study followed elite ultrarunners, cyclists and triathletes through events and training spanning 30 to 52 weeks.
  • Direct measurements during multi‑day races showed short‑term peaks of roughly six to seven times basal metabolic rate, translating to about 7,000–8,000 calories per day.
  • Modeled long‑term averages converged near 2.4–2.5 times basal metabolic rate, aligning with earlier proposals of a duration‑dependent limit.
  • Energy expenditure was measured with the doubly labelled water method, and athletes appeared to reallocate energy by unconsciously cutting non‑exercise activity.
  • Authors note a small, mostly ultramarathon cohort and reliance on training‑log modeling for yearlong estimates, leaving mechanisms such as nutrient absorption limits to future research.