- China's Ye Shiwen wins second gold in London Tuesday in 200m individual medley
- 16-year-old beat 400m individual medley world record by a second on Saturday
- John Leonard called Ye's swim 'unbelievable' and 'disturbing'
- IOC spokesman calls doping allegations 'sad' and 'pure rumor'
(CNN) -- How on earth could a teenage swimmer at her first Olympic Games knock five full seconds off her previous best performance? That's what has left so many people scratching their heads after watching China's Ye Shiwen smash the world record in the women's 400-meter individual medley.
The Chinese swimming prodigy's extraordinary swims during the first few days of the Olympics may have drawn praise from across the sport, but they've also raised suspicions of drug doping.
The 16-year-old world champion won gold Tuesday in the women's 200-meter individual medley, three days after coming from behind to take one second off the world record -- and a whopping five seconds off her personal best -- during her gold medal swim in the 400-meter individual medley.
The controversy over her record tear through the final 50 meters of Saturday's golden swim -- faster than the final leg of American champion Ryan Lochte's own gold medal performance -- began during the BBC's coverage of the race, when presenter Clare Balding turned to her co-presenter, former British Olympian Mark Foster, and asked: "How many questions will be there, Mark, about someone who can suddenly swim much faster than she has ever swum before?"
Swimmer under scrutiny after record win 
Chinese media weigh in on doping 
Chinese swimmer's 'suspicious' race John Leonard, the executive director of the American Swimming Coaches Association (ASCA) and the World Swimming Coaches Association, called Ye's swim "disturbing" and told the Guardian newspaper it brought back "a lot of awful memories" of doping scandals at previous Olympics.
International Olympics Committee spokesman Mark Adams called doping allegations against Ye "sad" and "pure rumor," and told CNN he had heard nothing from Olympics drug testers to suggest that anything was awry.
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But while Ye's swimming has caused the most controversy in the first week of the Olympics, the swimming prodigy herself isn't exactly an unknown quantity.
Born in the eastern Chinese city of Hangzhou, Ye began swimming at the age of six after her teacher noticed she had large hands and feet, according to China's Xinhua state news agency.
After winning the 50-meter freestyle swim in her peer group at the Zhejiang Province Games in 2006 at the age of 10, her coach predicted Ye would be an Olympic champion.
Ye joined the Zhejiang provincial swimming team in 2007 and China's national team the year after.
Ye arrived on the world stage in 2010 at the age of 14, winning a pair of gold medals at the Asian Games and two silvers at the World Swimming Championships in Dubai.
On her Olympic profile, Ye's most memorable sporting achievement is listed as "winning the 200m and 400m individual medley at the 2010 Asian Games in Guangzhou."
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But it wasn't until world champion Li Zhesi was banned in June 2012 for a positive drug test that Ye rose to the forefront of the Chinese swimming team.
Ye won gold in the 200-meter individual medley at the 2011 World Aquatic Championships in Shanghai, but finished outside the top three in the 400-meter individual medley.
Just one year later, Ye swam the race more than a second faster than any woman in history.
Ye has attributed her success to her training schedule and hard work. "If the coach asks me to practice 10,000 meters, I would never be a lazy player to swim 9,900 meters instead," the Beijing Morning News quoted her as saying.
But practicing hard and destroying the 400-meter medley record by storming through the final 50 meters faster than anyone else, man or woman, are two very different things, and Ye's golden performance quickly raised suspicions of drug doping from Leonard, one of the most respected names in the sport of swimming.
"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," said Leonard, who is also the executive director of the USA Swimming Coaches Association.
South African sport scientist Ross Tucker expressed concern on his Science of Sport blog about the vast difference between the relatively average times Ye swam in the first three legs of the 400 meter race and her faster swim through the final 100 meters.
"The conclusion that I would draw from this is that her 100m freestyle leg is disproportionately fast not only by comparison to Lochte, but also to her peers, and to the best 100m freestyle swimmers," Tucker wrote.
British Olympic Association chairman Colin Moynihan joined China's anti-doping chief in defending Ye, saying Olympic drug testing was "on top of the game."
"She's been through (anti-doping agency) Wada's programme and she's clean. That's the end of the story," he told reporters at a Tuesday news conference.
More: Visit CNN's Olympic center here
Ye has denied doping allegations, saying, "My achievements derive from diligence and hard work, I will never use drugs. Chinese athletes are clean."
Ye, along with many of her teammates, reportedly spent months training in Australia before the Olympics, and China's approach appears to be paying off.
Sun Yang won China's first ever men's gold medal in swimming in the 400-meter freestyle final just 25 minutes before Ye's record swim last Saturday, and the Chinese swim team has also netted several other swimming medals.
No one seemed more surprised about the outcome of the race than Ye herself, who said: "I dreamed of winning the gold medal, but I never ever expected to break a world record, I'm overwhelmed."
The head of China's swimming team, Xu Qi, wondered aloud why similar allegations haven't dogged other top swimmers in recent years.
"Ian Thorpe was called a genius, Michael Phelps got eight gold medals in Beijing. Ryan Lochte, Missy Franklin are both recognised as geniuses. There were geniuses in France and South Africa. We admit and accept these geniuses, but why can't a genius come from China, a country with a large population?"
One person who doesn't seem in doubt is Lochte himself. He said: "It was pretty impressive. And it was a female. She's fast. If she was there with me, I don't know, she might have beat me."
CNN Wires contributed to this report.
