It seems like a long time ago that Liu Xiang had to look up to a rival in the 110m hurdles.

It has been just about four years since Liu won gold at the Athens Olympics, back when he described himself as "a chaser" behind his idol, four-time world champion Allen Johnson.

But since his Athens gold and the world record he set in 2006, Liu has established himself as one of the world's fastest hurdlers and has shrugged off challenges from opponents.