Iditarod and Yukon Quest are both like this - I met someone (who had won the Yukon Quest) that started wearing a helmet mushing because he had passed out from exhaustion and hit his head.
edit/P.S. When just googling I saw something talking about if these races were cruel to the dogs. While obviously some people have (or continue to) treated their dogs poorly, I must say his dogs clearly lived to run. They were so cute and energetic. He talked about how a woman a couple decades ago schooled all the men in the sport by truly taking care of her dogs, and it seemed like that had a big effect on how he raised his dogs.
On multi-day ultra-endurance rides there is an issue where your neck will no longer support your head against gravity, called Shermers neck syndrome. https://sportcoaching.co.nz/shermers-neck-a-guide-to-neck-sy...
i think the most famous example of this is the RAAM - the race across america (https://en.wikipedia.org/wiki/Race_Across_America): "In length the RAAM is comparable to the Tour de France, but the races differ to a great extent. The courses of both races have varied over the years. However, in the Race Across America, the direction has always been from the west coast to the east coast of the United States, approximately 3,000 miles (4,800 km), making it a transcontinental event. More importantly, the race has no stages, i.e., it is in principle a nonstop event from start to finish, with the fastest competitors needing slightly over a week to complete the course."
https://www.transcontinental.cc/ The Transcontinental Race is the definitive self-supported bicycle race across Europe. At the sharp end it is a beautifully hard bicycle race, simple in design but complex in execution. Factors of self reliance, logistics, navigation and judgement burden racers’ minds as well as their physiques. The strongest excel and redefine what we think possible, while many experienced riders target only a finish.
The Transcontinental is a single stage race in which the clock never stops. Riders plan, research and navigate their own course and choose when and where to rest. They will take only what they can carry and consume only what they can find. Four mandatory control points guide their route and ensure a healthy amount of climbing to reach some of cycling’s most beautiful and historic monuments. Each year our riders cover around 4000km to reach the finish line.
There's also the Indian Pacific Wheel Race - https://www.indianpacificwheelrace.com
There are many, many smaller ones in many, many countries.
Well, people already do that too:
https://www.runnersworld.com/news/a35885288/barkley-marathon...
This is running instead of biking, but the same idea. I'm not quite sure why people subject themselves to this, but they do.
I still have no interest in doing it, but it was a very interesting look into the thoughts of someone who does.
In video game speedrunning, the communities surrounding >24 hour speedruns (e.g. Breath of the Wild 100%) have often set up rules allowing for breaks for runners to sleep. This prevents the speedrun from becoming a competition of who can sleep the least.