Many people struggle to run a mile; others can knock out a 10K on a whim. A few brave souls take on "ultramarathons" — races longer than 26.2 miles (42.2 kilometers). But how far can a human run before they just have to stop?
To answer that question, first we have to define what it actually means to "stop." Dean Karnazes holds the unofficial record for the longest run without sleeping, at 350 miles (563 km), which he ran over three and a half days in 2005. In 2023, ultrarunner Harvey Lewis set a new record in a type of long-distance race called a backyard ultra. In this type of competition, runners complete a 4.17-mile (6.7 km) loop every hour, on the hour, until there's only one runner left standing. Lewis ran 108 of those loops in as many hours (equal to 4.5 days), totaling 450 miles (724 km), with just a few minutes at the end of each hour to rest before setting off again.
