Usain Bolt rocked his huge frame back into his too-small chair, wrapped his arms behind his head and prepared to deliver his well-worn defense after another bombardment of doping-related questions at a news conference on Thursday.

Ahead of Bolt's return to London for this weekend's Diamond League meet, the script was supposed to be all about his happy memories from 12 months ago when the Jamaican lit up the Olympic stadium with another superlative triple-gold medal performance in front of 80,000 dazzled fans.

Yet the No 1 topic was the recent positive dope tests on fellow Jamaicans Asafa Powell and Sherone Simpson as well American Tyson Gay, leading one journalist to ask Bolt if the public could trust the fastest man in history.