Last person standing: The race with no finish line

Think you can run 4.16666 miles in an hour? Probably.

Could you do it again the following hour? Quite possibly.

How about the hour after that? The legs might be feeling it by now.

What if you had to do it every hour for the next two or three days?

It's hard to say exactly how long you'll be running for - because this race only finishes when there's one person left standing.

The trouble is, some runners can keep going for quite a long time. The current record - held by a Belgian dentist - is 75 hours, or 312 miles.

Welcome to Big Dog's Backyard Ultra, the toughest - and weirdest - race you've never heard of.