Jonah Lomu may no longer be a giant on the rugby field but this week the freshly buffed All Black legend takes on a new challenge in a body building contest, a report said Tuesday.

The 34-year-old's Test career was cut short by a kidney condition that required a transplant in 2004, but this week he will prove he has not lost his thirst for competition by entering the Wellington body building championships.

Although his rugby career has failed to reignite since the transplant, Lomu has not given up on the game and has signed for French third division side Marseille Vitrolles, which he is due to join in November.

While getting fit for his latest rugby stint, he was persuaded to give this weekend's body building championships a shot.

"I just started out wanting to get back in shape and it's just gone from there," Lomu he told Wellington's Dominion Post newspaper.

"I've always loved lifting weights, just ask the All Blacks, so it's been a lot of fun ... I can't wait to get up there on Saturday."

The veteran of 63 Tests between 1994 and 2002 and star of two World Cups is keen to stay fit for his young son Brayley. He has dropped his weight from 142 kilograms two years ago, aiming to take the stage at 114 kilograms.

"I've got a seven-month-old boy now and I want him to see me looking healthy and being healthy," he said.

"I want my son to see me as a 50-year-old with a six-pack, not a beer gut."

Of Tongan heritage, Lomu said covering himself in tanning oil will be a new experience.

"I've got the year-round tan but they reckon I need this."

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