Surpassing one's best time by milliseconds would be more credible.
The Chinese swimmner Ye Shiwen took seconds off her personal best to break the world record and win a gold medal in the 400m medley on Saturday, swimming faster in the last 50m than the winner of the men's event.
There is no evidence against her and all medal winners are drug-tested.
John Leonard - the executive director of the World Swimming Coaches Association - said her performance was "unbelievable".
I do have my suspicions.