It sounds tough. Now imagine doing it on crutches because you only have one leg.

That's exactly what Australia's most successful winter Paralympian Michael Milton has signed up for in the Australian leg of the Ultra-Trail World Tour.

Milton's left leg was amputated above the knee when he was nine years old due to bone cancer, and he went on to represent Australian in skiing and cycling in the Paralympics.

The prospect of climbing nearly 1000 stairs on their own are enough to leave some shaking in their boots, but Milton says it's the run that will test him the most on Saturday.

"On its own [the stairs are] a piece of cake, but at the end of 50kms and stuff for me it's an extra challenge that you just know is waiting for you at the end," Milton said.

"It's probably a little bit easier in some ways with hands and stuff like that, but the physical intensity of walking up nearly 1000 stairs, you've got to have some gas left in the tank for that."

Canberra-born Milton has already completed a marathon on crutches in just over five hours but expects the Katoomba-course to take almost 12 hours to finish.

With the rain forecast set to make things tougher, Milton says his biggest challenge will be to keep a smile on his face the whole way.

"At some stage along the course I expect to be asking myself, 'do I want to continue? Am I able to continue?'," Milton said.

"The first 10 times you ask that question it's going to be 'no'. I know that, but how many times before you start asking yourself before you start really considering the no answer and simply can't go any further?

"How much am I going to have to test and push myself to get going past all that?"

Milton has a long history in athletics and has twice completed the Kokoda Track, having also scaled Mount Kilamanjaro.

So if things get tough he will have those experiences to fall back on, but this is a man that loves testing himself.

"I'm into anything that I think will challenge and test me, that keeps me motivated to stay fit and healthy and keep training," Milton said.

"I'll be running with a mate of mine from school and I'm expecting a good day out. So far from my point of view, all the training that we've done, trips to the Blue Mountains for training, it's all been really rewarding and very fun."

Milton has been training for six months in the lead up, scaling Mount Ainslie up to six times a day before going up and down Mount Tennent in a seven-hour effort.

Safe to say Milton is thankful he's had ample time to "put the work in" but the actual event shapes as a different beast, with "about 2500 metres of climbing" to be done throughout the course.

"We'll see if I've done enough on Saturday."