A lightning-speed swim by a teenage Chinese swimmer has caused some raised eyebrows from some coaches and commentators, bemused at 16-year-old Ye Shiwen's stunning achievement.
Ye, who took gold in the 400m women's medley in a world record time of 4 min and 28.43secs - was faster than men's champion Ryan Lochte in the final 100m of freestyle.
BBC Sports presenter Claire Balding appeared to question the achievement of the teenage wondergirl during the coverage.
She asked her commentating companion, Olympian Mark Foster: “How many questions will there be, Mark, about somebody who can suddenly swim so much faster than she has ever swum before?”
He replied: "It was a five-second best time and it was the way she did it as well. Bearing in mind she is 16 years of age, and when you are young you do some big best times.”
John Leonard, the executive director of the World Swimming Coaches Association told The Guardian: "We want to be very careful about calling it doping.
"The one thing I will say is that history in our sport will tell you that every time we see something, and I will put quotation marks around this, 'unbelievable', history shows us that it turns out later on there was doping involved."
Arne Ljungqvist, the chairman of the International Olympic Committee's medical commission and a veteran anti-doping official, said there were currently no concerns about Ye's achievement.