Superman star Christopher Reeve's against-all-odds improvement has stunned doctors, who say it is the first documented case of such progress over paralysis years after catastrophic spinal cord injury.

They believe intensive physical therapy is key to the modest, though important, changes Reeve has seen since his injury in 1995. However, they cannot predict whether improvement will continue or if the same approach will help others with long-term paralysis.

"We are talking about an unprecedented amount of recovery. There is just no basis to talk about how much more to expect," said neuroscientist Naomi Kleitman, head of spinal cord injury research at the National Institute of Neurological Disorders and Stroke.

The first clear sign of change occurred one early November day almost two years ago, when Reeve twitched his left index finger. By then, he had been immobile from the neck down for more than five years, unable to feel or move anything. But the movement was the start of a slow rebirth of sensation and control that he says has changed his life for the better.

Reeve, who turns 50 on Sept. 25, still must use a wheelchair. All but one hour a day, he uses a ventilator to breathe. But he can feel human touch, experience pain and move his fingers, wrists and legs.

"His was the worst-case scenario," said Dr. John W. McDonald, who oversaw his treatment at Washington University School of Medicine in St. Louis. "Nobody in the world would have predicted he could recover."

Reeve was thrown from a horse seven years ago and landed on his helmet, breaking his neck and damaging the thumb-size bundle of nerves that carries messages between the brain and the rest of the body. At least three-quarters of the nerve fibers were severed, and what remained did not work. Over the years, his muscles withered, his bones thinned, and he suffered repeated bouts of infection and life-threatening complications.

After years of his own exercise efforts, the actor began in April 1999 an approach called activity-based recovery, which involves repeated electrical stimulation of the muscles. The idea is that constant motion could re-educate the remaining nerves in the spine to carry signals and perhaps even sprout new branches to connect to healthy fibers above and below the injury.

For an hour three times a week in his home, Reeve sat on an exercise bicycle while electrical stimulation made his legs pump the pedals. Similar stimulation was done to other muscle groups. Next he began weekly aquatherapy, working his muscles in a pool for two hours at a time.

McDonald described the results in a report in the September issue of the Journal of Neurosurgery: Spine, including an interview he did with Reeve during the summer.

Now, Reeve can tell hot from cold. He can feel about two-thirds of the normal sensation of being touched and half of the usual intensity of pinpricks. This ability to feel lets him know when he should shift his weight, so he can sit in a wheelchair up to 16 hours a day without getting pressure sores.

In the water, he can make flying motions with his arms and walk. However, he still requires around-the-clock nursing care, and out of the pool, he cannot raise his arms or walk without being held up.

Reeve told McDonald that knowing he can breathe on his own has relieved his terror of a ventilator failure, and life with his family is much more normal.

"They know I am healthier, stronger, and that on any day, I might have a surprising recovery," he said. For instance, after a recent session in the pool, "my ability to push off from the wall against resistance was about twice as strong as it was weeks earlier."

Gaining sensation has also been important. "It makes a huge difference if someone touches you on the hand, and you can feel it," he said. "You make a much more meaningful connection."

Typically, doctors tell paralyzed patients that most improvement occurs in the first six months with no hope of recovery beyond two years.

"The truth is, we don't know," said Dr. Kevin O'Connor, head of spinal cord injury recovery at Boston's Spaulding Rehabilitation Hospital. "Given this report, it's really unfair to patients to say there is a time limit."

Doctors say they also cannot be sure, from a single case, whether repetitive movements actually do revive the wiring of the spine to carry lost messages. But several said they believe Reeve's unusual course of physical therapy played a role in his recovery.

"I can't help but think it had something do with it," said Dr. John Jane, who treated Reeve at the University of Virginia soon after the accident. "People often begin to recover right away. The fact is, he did not. It's the late recovery that is so absolutely unique."

A study under way by McDonald, comparing 20 patients who get repetitive movement and 20 with usual care, may help answer this.

Reeve, certainly, hopes this is just the start.

"My recovery means everything to me, because while some people are able to accept living with a disability, I am not one of them," he said. "I want my life back."