UNSW prosthetics researcher uses the force

Making the world's fastest one-legged man even faster

Stacey Rigney, PhD student at the UNSW Graduate School of Biomedical EngineeringWorking with the world’s fastest man on one leg is one of the best highlights of researching prosthetics, according to PhD student Stacey Rigney who is supervised by Dr Lauren Kark, lecturer at the Graduate School of Biomedical Engineering. As part of her research, she spends time at the Australian Institute of Sport in Canberra, working with young athletes and equal world record holder for the T42 100m sprint, Scott Reardon.

Working with a world record holder

Scott, now 24, lost his right leg at the knee in a farming accident when he was 12, but has gone on to win world titles in water skiing and received a silver medal in the 100m sprint at his first Paralympic Games in London in 2012. He equaled the world record for the T42 100m at the 2013 Australian Athletics Championships at 12.14 seconds.

“He’s amazing and he’s so involved in the decisions that are made about his leg and his sport,” said Stacey. “In terms of research and designing new prosthetics, I can do something that I think is worthwhile, but it’s so good to hear what he thinks the priorities are at the coalface.”

Stacey explains that although continuous-shape carbon-fibre foot and lower limb prostheses have been used in competition since the late 1980s, there is no accurate modeling of how they affect amputee gait and there is limited understanding of their functional performance.

Developing a mathematical behavioural model

“Elite athletes and their coaches will just try changing the angles of the prosthetic attachment and then ask ‘how did that feel?’,” she said. “It’s very rudimentary. Rather than trying to design a new prosthesis, I’m trying to model its behaviour. We don’t know a lot about how they behave. I’m trying to develop a mathematical behavioural model for the prosthesis when it deforms and returns the energy back.”Stacey Rigney

She says that traditional gait analysis techniques do not work on prosthetics because they work like a spring. Usually in gait analysis, passive reflective markers are put on the knee, shin and ankle, the subject is filmed, and then computer programs join the dots into stick figures and determine the torques and mechanics involved.

“The problem is that’s relying on the fact that we have a rigid skeleton and foot,” explains Stacey. Consequently she’s had to change the method from solid mechanics to elastic continuum mechanics, using COMSOL software to study the mechanical behaviour and OpenSim to model the movement of muscles and calculate the forces.

“We can run simulations and say ‘if we change the angle that it’s connected to the limb to seven degrees instead of two degrees, will it make their gait more symmetrical? Will it make them faster?’”

"Traditional gait analysis techniques do not work on prosthetics because they work like a spring"

The first part of Stacey’s work involved materials testing of the prosthesis itself to determine how it performed when different forces were applied, and at different angles.

Stacey said that the Australian Institute of Sport is excited about the potential implications of her research, as it may be able to improve performance of the athletes using them.

World changing research

Stacey recently featured in The Sydney Morning Herald as one of the six women whose research would change the world.