source A bit too blatant as a runner uses a bike during a marathon. She was later disqualified and banned for life after being told on numerous occasions to get off.
The Boston marathon has strict entry requirements as they have so many applicants each year. They do this to keep the "riff raff" out and they still somehow get in. This year 3 runners were banned and they came from China. The Chinese government stepped in and banned the runners for life. I have no idea why runners would cheat if the race is that difficult and you aren't good enough. Does it go on your CV or something?
If we take a look at what is happening in China as running is a very popular sport today. With over 1000 marathon races a year which works out to around 3 races every day it seems they love running for some reason. Most marathon runners are short in stature and have a skinny build which probably means that 99 percent of the Chinese population should be fairly decent athletes.
I still don't get it though and it has to be a status thing among the Chinese people. Bragging rights and being allowed to run in a more prestigious race where you will only get found out as your fake times will only show how bad you really are. The Chinese really take running seriously it seems and nothing will stop them. Most people I know that run in competitive marathons do it for the enjoyment and cheating doesn't come into it.