25 July 2013 Last updated at 15:48 GMT

Usain Bolt: Failed drug tests a setback for the sport

Sprinting great Usain Bolt admits the recent positive drug tests of his Jamaican team mates have been a "setback" for the sport.

World 200m champion Veronica Campbell-Brown tested positive for a banned diuretic in June, before Asafa Powell was among a group of Jamaican athletes who failed drug tests in recent weeks.

Six-time Olympic champion Bolt stresses that he is "clean" and has been doing "phenomenal things" from a young age.