Using metabolic tracers and year-long training records, researchers modelled total energy expenditure in 14 elite endurance athletes. They found average daily energy use rarely rose above ~2.4–2.5× resting metabolic rate, though brief spikes (one >7× during a ~24-hour run) occurred. Sustaining higher averages for roughly 30 weeks was uncommon, with only four athletes modestly exceeding the predicted ceiling. The study supports a likely physiological cap but calls for larger, more diverse samples to confirm the limit.
Even Elite Athletes Hit a Metabolic Ceiling — Study Finds Limits to Sustained Calorie Burn
Using metabolic tracers and year-long training records, researchers modelled total energy expenditure in 14 elite endurance athletes. They found average daily energy use rarely rose above ~2.4–2.5× resting metabolic rate, though brief spikes (one >7× during a ~24-hour run) occurred. Sustaining higher averages for roughly 30 weeks was uncommon, with only four athletes modestly exceeding the predicted ceiling. The study supports a likely physiological cap but calls for larger, more diverse samples to confirm the limit.
12:54, 03.11.2025Science
Elite Athletes Are Human Too: A Biological Limit on Sustained Energy Use
New research suggests that even world-class competitors usually cannot sustain calorie burning far beyond a predictable biological ceiling. Using a gold-standard tracer method and detailed training records, scientists modelled year-round energy use in elite endurance athletes and found that prolonged averages above roughly 2.4–2.5 times resting metabolic rate are uncommon.
How the study was done
The analysis involved 14 highly trained athletes — runners, cyclists and triathletes — most aged between 30 and 44; two participants were female. Researchers estimated each athlete's total energy expenditure by having them drink water labeled with two metabolic tracers. Tracer levels in urine allowed precise calculation of calories burned during activity. Those measurements, combined with 52 weeks of training logs, were then used to model each athlete's maximum "metabolic scope" across a full year.
Key findings
Typical yearly averages: On average, these elite athletes rarely burned more than about 4,000 kcal per day — roughly 2.4 times their resting metabolic rate (RMR).
Short-term spikes: Brief, extreme bursts of energy use did occur. The highest metabolic scope recorded exceeded seven times a subject's RMR during an almost 24-hour run on the Appalachian Trail. Several ultramarathoners exceeded four times RMR during certain multi-day events.
Sustained limits: Although the body can temporarily exceed 2.4× RMR, sustaining a higher average over long stretches (about 30 weeks of training and races) was rare. Only four athletes surpassed the modelled ceiling after 30 weeks, and their margins were modest (around 2.7× RMR).
The study authors conclude that "athletes in this study did not meaningfully exceed the proposed metabolic ceiling," while noting that exceptional world-record ultra-endurance efforts may involve higher expenditures.
What this means — and what we still don't know
The findings add to growing evidence for a fairly hard limit on how much energy humans can sustain over months at a time, even at elite fitness levels. However, the sample was small and skewed (only 14 athletes, mostly male and limited age range), so broader and more diverse measurements are needed to define the true boundaries of human endurance.
Publication: The study was published in Current Biology.