Ultra-endurance athletes and the metabolic ceiling.
Level 4 - case-series / case-control
Small observational physiological cohort without a comparison control group.
PubMed 41118725 · doi:10.1016/j.cub.2025.08.063
What was done
Researchers tested the duration-dependent metabolic ceiling model in 14 highly trained, elite, and world-class ultra-endurance athletes (12 males, 2 females; mean age 37.2 ± 7.0 years). Total energy expenditure (TEE) and basal metabolic rate (BMR) were measured to calculate metabolic scope (MS = TEE/BMR) using doubly labeled water during competitions lasting ~24 hours to ~13 days, as well as during low- and high-workload training weeks. Predictive equations relating MS to exercise volume were generated and applied to participants' long-term training records to estimate maximal MS across 1-, 3-, 6-, 12-, 30-, and 52-week intervals.
What was found
For competitions and training intervals up to 12 weeks, maximum MS approached but did not exceed the theoretical duration-dependent ceiling. At 30 and 52 weeks, 4 of the 14 athletes exceeded the proposed 2.5× BMR asymptote (highest individual value: 2.74× BMR). However, group mean MS remained below the 2.5× threshold at 30 weeks (2.43 ± 0.17; TEE: 4,085 ± 642 kcal/day) and at 52 weeks (2.39 ± 0.17; TEE: 4,020 ± 641 kcal/day).
Why it matters
The study provides empirical validation in elite athletes for the concept of a biological constraint on sustained human energy expenditure, reinforcing the idea that long-term human energy throughput rarely exceeds ~2.5 times basal metabolic rate.
Limits
The sample size is very small (n = 14) and heavily skewed toward male athletes (12 males vs. 2 females). Long-term energy expenditure over 30 and 52 weeks was estimated using predictive equations applied to training logs rather than continuously measured via doubly labeled water throughout the entire multi-week spans.
Cited by
- supports Scientific data show an inverse relationship between the duration of an endurance athletic event and the maximum metabolic power output sustained per day.