Ultra-endurance athletes can burn up to 8,000 calories per day

A'metabolic ceiling' still keeps the body in check, even when running hundreds of miles at a go. Breakthroughs, discoveries, and DIY tips sent every weekday. They're not only inspirational, but are also testing the limits of human biology with their mental grit and muscle strength by logging hundreds of miles and days at a time. According to a study published today in the journal even the most extreme endurance athletes cannot surpass a certain level of calorie burning. What is the metabolic ceiling?