The world will never know if Liu Xiang would have successfully defended his 110 m hurdles Olympic title; all that is certain is that a persistent Achilles tendon injury proved a bigger hurdle than any of the barriers he is used to flying over.

Feng Shuyong, head coach of Team China, said at a press conference just 20 minutes after Liu's exit from the Beijing Olympics, that the hurdler had no option but to withdraw after all attempts at easing his pain had failed.

Liu has been battling his Achilles tendon problems for the past four years.

Li Zhao, a specialist from the sports medicine center at Shanghai Chen Xin Hospital, told China Daily: "I think it was the right decision for Liu Xiang, because injuries like that can be very serious.

"Athletes are always at risk of Achilles problems, especially hurdlers who put a lot of repeated pressure on the tendon in training."

Liu's body was simply unable to repair the injured tissue because of the persistent stress on the tendon.

In the end, the structure of the tendon is altered and that is what causes the pain, he said.

"Liu is only 25, and will have many more opportunities to win medals.

"But right now, he needs to rest for at least three months," Li said.

Most Asian hurdlers do not reach their peak until they are between 25 and 27 years old, he said.