When ultra-runners lace up for races that stretch hundreds of miles and days, they’re not merely testing their mental grit and muscle strength—they’re probing the limits of human biology. Reporting in Current Biology, researchers found that even the most extreme athletes cannot surpass an average “metabolic ceiling” of 2.5 times their basal metabolic rate (BMR) in energy expenditure.
Ultra-endurance athletes test the metabolic limits of the human body
