A revolutionary new exercise system has been developed to help people with multiple sclerosis (MS) build muscle mass and improve their physical health.

Researchers at the University of Sydney Faculty of Health Sciences have developed a specially adapted bicycle which uses electronic stimulation to involuntarily activate the leg muscles to drive the pedals, similar to methods used for spinal cord injuries.

Usually people with MS, a disease of the central nervous system, have a less active lifestyle, and the researchers are investigating how those with limited mobility and extreme fatigue can get the benefits of more exercise.

Lead researcher Dr Che Fornusek said results from early trials had been positive for those who still have sensation in their legs.

"Their leg muscles grew and the participants reported better blood flow, better skin and their legs felt better," Dr Fornusek said.

"Their legs were less stiff. Larger muscle mass in itself is important because it has an effect on the central metabolism and if you've got a decent muscle mass it can give you protection from metabolic diseases like diabetes."

Dr Matthew Miles, chief executive of MS Research Australia, said it was important to find new treatments and interventions for those suffering from the progressive form of the disease.

"It's a wonderful and novel approach," Dr Miles said.

"The ability to take what we know in spinal disease and to look at how that might affect other diseases such as MS is of great importance to us."

Since she was diagnosed with MS 18 years ago, 61-year-old former teacher Jill Hodder has often struggled to deal with her decreasing mobility, and now uses a wheelchair.

"I think it's more frustration in things. And when I'm tired it's twice as bad," Ms Hodder said.

"And I'm usually worse in the afternoon."

Researchers say exercise is beneficial for people with MS

But thanks to this trial, the former gym junkie now has the opportunity to do some exercise.

"I remember one day I was at the MS gym and someone said 'hey, you've got muscle definition', which I never had. And I was stronger basically," she said.

"I know if I don't exercise I just seize up."

Dr Fornusek said the field has changed its position on exercise and the heating of the body, which 10 to 15 years ago was thought to have a negative impact on the disease.

"Basically we know that that's got nothing to do with the disease process getting worse, which is an immune response," he said.

"So now that we know that we can exercise them they can heat up and it's not going to do them any harm, there's no reason that they can't exercise."

Through the study, he hoped to determine whether increased activity might even slow the MS disease process.

"These people with MS, if they don't do exercise because they're already inactive it compounds the disability they have at the moment."

A further trial is currently underway with results expected in a year.