BERLIN, Germany (AFP)— At least 30 per cent of those who competed at the 2011 IAAF World Championships admitted to having used banned substances during their careers, according to a report.

The research was carried out by Germany’s University of Tuebingen and America’s Harvard Medical School in 2011, but legal wranglings meant the report was only recently made public.

The study, commissioned by the World Anti-Doping Agency (WADA), calculates that at least 30 per cent of the athletes at the world championships six years ago were doping, but admits the real figure could be even higher.

Only 0.5 per cent of those who competed at the 2011 worlds in Daegu, South Korea, failed regular testing.

The team from the German university say their findings were delayed for so long due to talks between WADA and athletics’ governing body, the IAAF, as to how the study should be published.

“I have long demanded that this study be published,” German athletics federation president Clemens Prokop told AFP subsidiary SID.

“In the anti-doping battle, there can only be one guideline: total transparency.

“The figures are clear.

“Aside from the fact that I know the questions the researchers asked and how robust the data is, the results have a terrifying value.”

When the research team asked the same questions to athletes at the 2011 Pan-Arab Games held in Qatar, the figure was even higher at 45 per cent.

More than 5,000 athletes competed at the two events and 2,167 were asked if they had taken banned drugs in an anonymous survey.

Doping has cast a dark shadow over the sport in recent years after the Russian athletics team was banned from the 2016 Rio Olympics after an investigation into a state-sponsored doping programme.

Re-testing of old samples using new methods by the International Olympic Committee (IOC) has found more than 100 athletes used banned substances at the 2008 and 2012 Olympic Games.