As if walking the Kokoda Track wasn't challenging enough, four jockeys and celebrity Kris Smith are planning to do in half the standard time.

But sickness, a thrilling end to the Sydney jockeys' premiership and a lack of trekking training are so far hampering that goal.

Leading Sydney jockey Hugh Bowman will join model Smith and fellow hoops Kathy O'Hara, Stephen Baster and Corey Brown in the Papua New Guinea forest at the beginning of next month.

But Bowman's preparation for the four-day, 96-kilometre trek has been far from ideal.

He says he's been under the influence of the flu, while the opportunity to take the final few weeks of the season off evaporated when Bowman wrested the Sydney premiership lead from Brenton Avdulla.

"I haven't done any (training) yet," Bowman said.

"All I've done is bought my boots and ... (done) a bit of walking in them.

"I'm under no illusions. I'm hoping my fitness levels might help but just because I'm fit doesn't mean it won't be a challenge."

Kokoda has special significance for Bowman whose great uncle and first cousin twice removed died during World War II.

There's a family history of military service in O'Hara, whose parents, half-brother and grandfather served in the military.

"I did a 24 kilometre walk in a national park the other day but I've got to do that every day for four days when I go there," she said.

"At least, I've done one day."

Baster, who can run 10km in under 40 minutes, forecast former rugby league player Smith tougher than the quartet half his size.

"Kris Smith's arms are probably twice the size of my legs," he told Sky Sports Radio.

"He's a fit man. But I reckon he'd be weighing in at close to 100kg (and) might find have more trouble going up the mountains than us little mountain goats."

Funds raised will be split between the National Jockeys Trust and brain cancer charity, The Mark Hughes Foundation.

Donations can be made at walking2help.com.au