Long-term fitness training could slow the progression of Parkinson's disease, according to research by the University of Houston College of Pharmacy.

The study suggests that exercise protects key cells involved in maintaining function and movement.

"This research provides scientific evidence that long-term endurance exercise protects brain mitochondria and dopamine-producing neurons from undergoing progressive degeneration as demonstrated in the chronic mouse model of Parkinson's disease," said Professor Yuen-Sum Lau.

Exercise must be long-term to sufficiently produce neuroprotective benefits, he added.

The next phase of the research will consider whether exercise could reduce or even replace the use of medication at the early stage of the disease.

Parkinson's occurs because of a loss of nerve cells in the brain which produce dopamine.

This chemical allows messages to be sent to the parts that co-ordinate movement, so the reduction in cells producing it means the brain is unable to function normally.

Exercise is especially important for people with the disease as they tend to get stiff and rigid in their joints and muscles, the Parkinson's Disease Society explains.