Weight training can help ward off Alzheimer's disease by making the brain stronger, according to new research.

Weight or resistance training not only strengthens your muscles but your brain and could help prevent Alzheimer's disease, according to new research.

A recent trial led by the University of Sydney in collaboration with the Centre for Healthy Brain Ageing at UNSW and the Univeristy of Adelaide found increased muscle strength led to improved brain function in adults with Mild Cognitive Impairment (MCI).

Mild Cognitive Impairment defines people who have noticeably reduced cognitive abilities such as reduced memory but are still able to live independently, and it is a precursor to Alzheimer's disease.

It's not the first study to show such exercise helps cognitive function, but it is the first to show that the amount of improvement MCI patients made was very much dependent on the strength gains they got from the training, said lead author Yorgi Mavros.

Bascially, the stronger people became, the greater the benefit for their brain.

"To get the most benefit for the brain you need to be exercising at a high intensity to maximise your strength gains," Dr Mavros added.

The trial, which was part of a wider study into cognitive function and resistance training, involved 100 adults with MCI, aged between 55 and 86.

They were divided into four groups: those doing resistance exercise and computerised cognitive training; resistance exercise and a placebo computerised training (watching nature videos); brain training and a placebo exercise program or placebo physical exercise and placebo cognitive training.

Participants prescribed the resistance training performed weight-lifting sessions twice a week for six months, working at least 80 per cent of their peak strength.

As they got stronger, the amount of weight they lifted was increased.

The results of the trial, published in the Journal of American Geriatrics, showed overall cognition improved significantly after resistance training, as measured by tests including the Alzheimer's disease Assessment Scale for cognition.

The cognitive training and placebo activities did not have this benefit.

MRI scans have also showed that a particular part of the brain got thicker and bigger as a result of the strength training, said Dr Mavros.

The results are particularly good news for those older patients with arthritis who find walking or jogging painful.

"Something like strength training is a bit more accessible to these people because quite often you're seated and the exercises are modifiable to work around some of the pain you might be getting," Dr Mavros said.