How Far Is Too Far for Ultra-Endurance Athletes? This Study of Metabolism Found Out

October 23, 2025

Ultra-endurance athletes can push their bodies to the limits, whether on a racecourse or bike path or in a swimming pool. But where does that limit end? To find out, a group of ultramarathoners, cyclists and triathletes joined anthropologists to test the limits of human energy expenditure, burning thousands of calories a day. Most ran an average of 4,000 miles over the course of one year. Smithsonian magazine