Austin Whitney and Rob Summers share a common bond. Both were paralyzed in car accidents; both were told they would never walk again. Thanks to University of California researchers, both have done the seemingly impossible: They have taken steps on their own.

Both revelations came within a week. Whitney, 22, stood up from his wheelchair at UC Berkeley's commencement ceremony May 14, and the graduating senior walked across the stage aided by an exoskeleton created by UC Berkeley engineers. Summers, 25, a former college baseball pitcher who has moved to Los Angeles, now can remain standing and take steps on a treadmill, aided by an experimental treatment developed at UCLA.

These breakthroughs point to the innovative ways UC researchers are working to restore mobility in disabled and paralyzed people. In addition to exoskeleton work at UC Berkeley, UC Santa Cruz engineers also are advancing the technology. While UCLA is exploring the use of epidural stimulation, a therapy developed at UC Irvine that made paralyzed rats walk again has become the world's first embryonic stem cell treatment tested in humans. For Whitney and Summers, these developments represent giant steps.

"The second I pressed the button and stood up, I was flooded with a series of emotions," said Whitney at a news conference following commencement. He described how the highs and lows of his life flashed through his mind as he was walking, from the instant his legs were paralyzed in a car accident four years ago, to the day he learned he got accepted into UC Berkeley.

Whitney's extraordinary walk has been in the works since last fall, when he connected with Homayoon Kazerooni, professor of mechanical engineering, and his team of researchers. The UC Berkeley engineers have been creating exoskeletons, a type of wearable robotic, to improve the mobility of paraplegics.

"Thanks to the work of professor Homayoon Kazerooni and his team of graduate students ... people with permanent mobility disorders can regain mobility," said UC Berkeley Chancellor Robert Birgeneau in his address to the new graduates shortly after Whitney's walk. "This achievement, as it was demonstrated to us today, embodies the public mission and indomitable spirit of Berkeley."

Summers was completely paralyzed below the chest after being struck by a vehicle in a hit-and-run accident in July 2006. Today, he is able to reach a standing position, supplying the muscular push himself. He can remain standing and bearing weight for up to four minutes at a time (up to an hour with periodic assistance when he weakens). Aided by a harness support and some therapist assistance, he can make repeated stepping motions on a treadmill. He also can voluntarily move his toes, ankles, knees and hips on command.

These unprecedented results were achieved through continual direct "epidural electrical stimulation" of the subject's lower spinal cord, mimicking signals the brain normally transmits to initiate movement. Once that signal is given, the research shows, the spinal cord's own neural network, combined with the sensory input derived from the legs to the spinal cord, is able to direct the muscle and joint movements required to stand and step with assistance on a treadmill. V. Reggie Edgerton, distinguished professor of integrative biology and physiology and of neurobiology at UCLA, helped develop the treatment.

"This procedure has completely changed my life," said Summers. "For someone who for four years was unable to even move a toe, to have the freedom and ability to stand on my own is the most amazing feeling. ... I believe that epidural stimulation will get me out of this chair."