AERIAL SKIING: Lydia Lassila fears she could be just one jump away from having to pull the pin on her aerial skiing title defence at next year's Winter Olympics with herniated discs playing havoc with her preparations.

On the surface the three-time Olympian appeared to be on track after two years out of the sport, capturing three second placings in World Cup events this season.

But the 31-year-old has a troubling back condition and is concerned a disc may rupture at any time during practice or competition.

"I've had a bit of a back issue which I haven't let on," she said ahead of a World Cup event at the 2014 Olympic host city Sochi this week.

"It happened in December. I have some herniated discs in my back. It happened in Ruka (Finland) and I couldn't jump for ten days."

Lassila, who had a baby during her hiatus from the sport, said the troubling aspect was that doctors have yet to figure out the exact nature of the problem or how best she should manage it.

"It's the question I have been asking (what to do)," she said.

"I can't really go on like this not knowing if it is going to go the next jump. I've just been quite scared and frustrated."

Lassila said it would be logical "to stop, go home and try to get it better rather than just pounding it every week" but added that rest and rehabilitation between events does seem to help.

"We've kind of just been trying to figure it out. It just means I can't train during the week," she said.

"On paper things are looking ok. I've had some podiums and am No.2 in the world but things haven't been going that well for me."

Lassila said part of the problem may have been lifting her son Kai who is now 21 months old - because she felt from a general fitness perspective she'd never been in better shape.

She'll aim to keep fit enough for next month's world championships in Norway but is constantly re-assessing her program.

"It is feeling better this week and I've had a bit of rest so hopefully it's ok ... but no one really knows," she said.

"Right now I'm just focusing on the worlds and working out how to do enough jumps to be safe.

"It's been quite challenging mentally being able to perform especially after two years off."

Meanwhile two Australians have moved directly through to the final of the snowboard halfpipe competition at the Sochi World Cup test event.

Nate Johnstone and Holly Crawford made it through to Thursday night's decider while defending Games champion Torah Bright and Scott James will have the chance to qualify through the semi-final.

Glenn Cullen
AAP