Chinese officials are furious over allegations that Olympic swimming sensation Ye Shiwen benefited from doping, calling for an apology from the U.S. head of the World Coaching Association called her record-shattering victory disturbing.
The 16-year-old Ye, who won gold in both the womens 200-meter and 400-meter events, has vehemently denied using performance enhancing substances, an assertion upheld by the International Olympic Committee (IOC) who says they test the first five athletes to place in any competition.
The IOC says it expects to complete some 5,000 tests - including those for both blood and urine - during the course of the Olympics.
How is testing completed?
According to the IOC, about 50 percent of athletes will be tested at random before, during or after any Olympic event.
Any athlete ranked in the top five is automatically subjected to doping control tests, with results returned in as few as 24 hours.
Athletes chosen for testing have one hour to report to a doping control station. While there, the athletes remain under the constant supervision of a same-sex agent while both urine and blood tests are performed.
The tests are then separated into two batches labelled A and B, which are made anonymous before being sent to the Olympic anti-doping laboratory.
The testing is carried out using sample 'A', with 'B' being tested only if their is a positive finding or abnormal result.
All Olympic samples are stored for eight years.
What substances are officials looking for?
Testing is done on some 240 prohibited substances including steroids, diuretics, hormones and masking agents outlined by the World Anti-Doping Agency.
What happens if an athlete tests positive?
Once an athlete has tested positive, and is identified they can request testing of the second sample. Meanwhile a hearing is held with the athlete, the Olympic Disciplinary Commission, and the sport's national federation. The Disciplinary Commission will then make a decision which is forwarded to both the athlete and their National Olympic Committee.
The athlete then has the option to appeal the ruling at the Court of Arbitration for Sport.
2012 Olympic athletes facing bans or returning from them
- Albanian weightlifter Hysen Pulaku was banned after testing positive for an anabolic steroid on Saturday.
- St. Kitts and Nevis sprinter Tameka Williams admitted to taking a banned substance.
- On Wednesday, traces of a banned diuretic was found in the urine sample of Uzbekistan's sole gymnast Luiza Galiulina.
- French steeplechaser Nordine Gezzar was suspended from the French team last week after testing positive for a banned substance. He is appealing the decision.
- American Justin Gatlin, a 2004 Olympic gold medalist in the 200-meter race, returned to the Olympics this year after a four-year doping ban.
- British cyclist David Millar returned to the Olympics after a two-year ban for using banned substances.