London: Scientists have restored function in muscles paralysed by conditions such as motor neuron disease and spinal cord injury by artificially controlled-muscles using light.

"Following the new procedure, we saw previously paralysed leg muscles start to function," said Linda Greensmith, professor at the University College London's institute of neurology.

This technique has significant advantages over existing ones that use electricity to stimulate nerves which can be painful and often results in rapid muscle fatigue.

Moreover, if the existing motor neurons are lost due to injury or disease, electrical stimulation of nerves is rendered useless as these too are lost, said Greensmith.

The technique involves transplanting specially-designed motor neurons created from stem cells into injured nerve branches.

These motor neurons are designed to react to pulses of blue light, allowing scientists to fine-tune muscle control by adjusting the intensity, duration and frequency of the light pulses.

"This new technique represents a means to restore the function of specific muscles following paralysing neurological injuries or disease," said Greensmith.

According to researchers, within next five years or so, they hope to undertake this ground-breaking approach into human trials.

Muscles are normally controlled by motor neurons, specialised nerve cells within the brain and spinal cord.

The light-responsive motor neurons that made the technique possible were created from stem cells by Ivo Lieberam of King's College London.

The study was published in the journal Science.