To prove you're fast, you run some other marathon in a fast time. But... what if you take a shortcut? Yes, some people do that. Runner's World had an interesting article about the phenomenon, which included an anonymous interview with a fireman who had cheated this way. The fireman got snagged by the fact that marathon running is a public sport. Results get posted publicly. Photos get posted publicly. And so forth. And some runners have made it their hobby to track down cheaters by looking at numbers that don't add up.
The fireman is not too happy:
He suspects three or four people know that he cut the course, including his sister. One of his coworkers confronted him after the 2013 race, but they have not discussed it since. “It’s what firemen do with bad calls and bad situations; they don’t talk about it.”
His wife, also a runner, does not know. He said he plans on telling her. But he fears if his name gets out, he will have to retire from his job early. “I have a reputation,” he said. “This is very bad.”
Some are feet of fleet
Others simply cheat.