Andy Murray's fitness coach Jez Green has said that he is "amazed" at the athleticism of which the US Open champion is capable.

Green, who has worked with Murray for five years, was speaking ahead of next week's season-opening Grand Slam in Melbourne.

Murray enters the tournament - where he faces Dutchman Robin Haase in the first round - in fine form, having captured Olympic gold and his first Grand Slam title last year.

Green believes that the Scot's speed across the court is a key asset to his game, but also said that he retains the brute strength needed for baseline rallies.

"I still find it hard to believe all the things that he can do," Green told The Times. "What you're seeing in this generation is a group of guys with incredible genetics.

"Andy is naturally fast, but he is also so strong: on his best day, he can do 27 pull-ups and push 300lb on the leg-press. He could probably run a 50-second 400 metres if he trained for it.

"He's been clocked at moving at ten metres per second over very short intervals, maybe even as short as a single step, which is as fast as Usain Bolt. I'm not saying he is that fast over 100m, but he has great acceleration when he is chasing down a drop shot."

Murray has twice reached the final of the Australian Open.