Overview
- The peer-reviewed Current Biology paper followed 14 elite ultra-endurance athletes for up to a year using the doubly labeled water method and detailed training logs.
- Direct measurements during races reached roughly 6–7× basal metabolic rate, with reported burns of about 7,000–11,000 calories per day, yet 30–52 week averages settled near 2.4–2.5×.
- As training loads rose, non-exercise activity declined, indicating energy reallocation away from fidgeting, incidental movement and other daily tasks.
- Authors and independent experts caution that the cohort was small and some estimates relied on assumptions, and they acknowledge potential outliers who might operate above the observed long-term ceiling.
- A digestion and nutrient-absorption limit is the leading hypothesis for the cap on sustained expenditure, though evidence from elite cycling and other data keeps the precise mechanism and universality under study.