Sam Willoughby admits that he has his days.

Which is understandable.

After all, he's tackling a physical and mental test that few could endure.

And it's a slog, especially for an elite athlete.

"I was at the point that I was insecure leaving the house. I didn't want to be seen in a wheelchair. I didn't want to be seen struggling," he admits.

"Always, my whole life I was Sam the successful athlete, and then all of a sudden in a blink of an eye, you don't want to bend down and pick something up in front of someone because you don't want to see them see you struggle."

BMX rider Sam Willoughby works with trainer and neuro recovery specialist Shane Paulson.

Sam is sitting in a dining chair speaking to us at his home in San Diego, California.

That, in itself, is remarkable in that not so long ago he couldn't sit up on his own.

The South Australian is a two-time world BMX champion, and won an Olympic silver medal in London.

A training crash in late 2016 left him a tetraplegic.

He broke his neck when he flipped off his bike at his regular training track just a few minutes from his house and was left paralysed from the chest down.

"I just remember feeling like my legs were way off in the distance," he says.

"Everything was just switched off and that was pretty scary, and at first it was just my legs and then five or 10 minutes later my arms went away."

Discipline essential to recovery

We're here to see Sam's rehabilitation therapy in his cramped garage, where bike wheels hang from the ceiling and helmets are piled up in corners.

There's an old framed photo of a smiling Sam in a cycling jersey sitting dusty on a bench, next to some scattered tools.

A painted Australian flag on a sign sits propped against a wall.

As an athlete, Sam was used to a tough training regime and he's applied that disciplined process to his recovery.

"As sickening as this sounds, I enjoy the struggle. Something about that has always been, even in sport, when my best times came, after a struggle," Sam says.

Every day he and his trainer Shane Paulson work for hours in the garage stretching and strengthening Sam's paralysed limbs.

Alise Willoughby is also a world champion BMX rider and says Sam's work ethic will help him reach his goal of walking again.

He's able to stand between parallel bars with minimal support, do pull ups and crawl along a mat that the therapist lays out in the backyard.

"He blocks my knees to help me pull myself up," Sam says about the therapy.

"Once I am up, I am locked in and I can stand there. Some days I have stood for as long as 20 minutes."

His progress has exceeded all expectations. After the accident he could barely move at all.

"I was pretty close to a vegetable at one point," he says.

Neuro recovery specialist Shane Paulson describes Sam's recovery as "inspiring".

"It's challenged me in a new way because I've learned that it's not always based on your experience or the science," he says.

"Sometimes people overcome things that you would never expect."

'You just find a new groove in life'

Sam Willoughby helps mentor and train his wife Alise who is also a BMX world champion and Olympic silver medallist.

Sam's wife Alise is also a BMX world champion and Olympic silver medallist.

The pair delayed their wedding after the crash, but were married at New Year.

Sam was able to stand for the ceremony with special knee braces, achieving a goal he had set.

"In Sam's instance, we knew that he would put the work in and there would be change because of the amount of work ethic no matter what he does in life. It was going to get better," Alise says.

"You just don't know how long this is going to take. So it is happening slowly but surely and he's still chipping away, and you just find a new groove in life."

He's now helping coach and mentor Alise and other BMX riders at the very track where he fell.

Coaching is a positive outlet as he continues his treatment.

"I don't see anything that he wouldn't be able to overcome at this point just because he seems to prove everyone wrong," trainer Shane Paulson says.

Sam says he doesn't set goals right now.

"It's unrealistic to expect myself to jump off this chair and walk around the house, but if I had a dream it's to be able to walk unassisted one day," he says.

For now, he's just persisting one day at a time.