There are regularly 24 hour races and I've done a few myself. 100 miles in 24 hours isn't that hard. The record was just recently set at 192.25 miles (309.4 km):

https://www.runnersworld.com/news/a37465691/sania-sorokin-24...

There are also 48 hr and 7 day races. Sleep is necessary somewhere between those two points, though two guys just went 85 hours with basically no sleep:

https://www.bigsbackyardultra.com/

That's a race where every hour on the hour you have to complete 4.166 miles. You get as much rest as the balance of your time after you complete a lap till the next hour begins. Most competitors complete a lap in around 48-52 minutes. The race continues until there is only one runner left to complete a lap.

Then we have Cliff Young who ran 875 km in 5 days - at the age of 61.

https://www.farmprogress.com/blog/cliff-young-farmer-who-out...

Humans can effectively run forever if it weren't for needing sleep, or eventually, needing to replace fat stores.

> Previous estimates, when accounting for glycogen depletion, suggest that a human could run at about a 10 minute per mile pace, which allows existing fat stores to be converted to glycogen, forever. The only limit to our eventual mileage, therefore, is our need for sleep. https://nikomccarty.medium.com/how-far-can-humans-run-d5c97f...