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)

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-hour-world-record/ 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/ 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.