Cameron Smith's unquenchable thirst for self-improvement and a remarkable functional capacity to play rugby league are the secrets to his indestructibility, says Kangaroos elite performance manager Troy Thomson. 

As the 34-year-old Kangaroos captain prepares for his 55th Test in the World Cup semi-final against Fiji, NRL.com spoke to Thomson about the qualities that have enabled Smith to play at such a high standard for so long.

Thomson has a lengthy association with Smith in a training capacity, stretching back to his days as a Norths Colt (in Brisbane) and then for a decade at the Melbourne Storm.

When Smith's former teammate Matt Geyer cracked the joke about him being "a footballer in an accountant's body" it entered the lexicon of ways to describe the Kangaroos captain.

But despite never being one of the fastest, strongest or biggest footballers, in one sense Smith perhaps has the ultimate footballer's makeup, as Thomson explained.

"Functionally, in the sense of his ability to play rugby league, I don't think I have seen anybody stronger," Thomson said.

"In the functional movements he has to do, like in controlling a tackle, he has this innate ability to avoid injury and I think that comes from his vision in a game.

"Many times you think he is going to get smashed, but he can just turn his body due to his game awareness.

"If you look at the way he is built, he is very strong through his core and in rugby league to have the ability to keep that part of his body stable and strong has helped him play footy and kept him relatively free of injury.

"But there is a lot if genetics in there. He has this in-built ability to play rugby league."