A 39-year-old man who was completely paralyzed for four years has been able to voluntarily control his leg muscles and walk again, with the help of a "robotic exoskeleton" device.

University of California-Los Angeles researchers said the man was able to regain his ability to walk, with assistance, during five days of training —and for two weeks afterward — using the device.

It marks the first time that a person with complete paralysis has regained enough voluntary control to actively work with a robotic device designed to enhance mobility — helping to improve his cardiovascular function and muscle tone.

In a report on the advance, to be published by the IEEE Engineering in Medicine and Biology Society, UCLA researchers said the breakthrough advance combines a battery-powered wearable bionic suit that enables people to move their legs in a step-like fashion, with a noninvasive spinal-stimulation procedure.

"It will be difficult to get people with complete paralysis to walk completely independently, but even if they don't accomplish that, the fact they can assist themselves in walking will greatly improve their overall health and quality of life," said V. Reggie Edgerton, a UCLA professor of integrative biology and physiology, neurobiology, and neurosurgery who helped lead the research team.

The robotic device is manufactured by California-based Ekso Bionics which captures data that enables the research team to determine how much the subject is moving his own limbs, as opposed to being aided by the device.

"If the robot does all the work, the subject becomes passive and the nervous system shuts down," Edgerton explained.

The patient at the center of the UCLA research, Mark Pollock, lost his sight in 1998 and fell from a second-story window in 2010 and suffered a spinal cord injury that left him paralyzed from the waist down.

At UCLA, Pollock made substantial progress after receiving physical training and spinal stimulation — preparing him to use the exoskeleton device.

"In the last few weeks of the trial, my heart rate hit 138 beats per minute," Pollock said. "This is an aerobic training zone, a rate I haven't even come close to since being paralyzed while walking in the robot alone, without these interventions. That was a very exciting, emotional moment for me, having spent my whole adult life before breaking my back as an athlete.

"Stepping with the stimulation and having my heart rate increase, along with the awareness of my legs under me, was addictive. I wanted more."

The data showed that Pollock was actively flexing his left knee and raising his left leg during and after the electrical stimulation; it wasn't just the robotic device doing the work.

"For people who are severely injured but not completely paralyzed, there's every reason to believe that they will have the opportunity to use these types of interventions to further improve their level of function. They're likely to improve even more," Edgerton said. "We need to expand the clinical toolbox available for people with spinal cord injury and other diseases."

Edgerton said it may take years for the new approach to become widely available, but he believes it will eventually help to significantly improve quality of life for patients with severe spinal cord injuries, and to help them recover multiple body functions.