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By Erika Edwards
(NBC News) Researchers at the University of Louisville say four paralyzed men are now able to move certain muscles in their legs thanks to a new implant.
An electrical stimulator implanted on the spinal cord makes it possible.
The four patients taking part in preliminary trials are now able to flex their toes, ankles and knees on their own.
The implanted stimulator is retraining the nerves in the legs to work with the brain again.
"This is a very, very low-level stimulus that is re-awakening the circuits to cause the circuits to remember what they used to do," explains Dr. Grace Peng of the National Institutes of Health.
Patient Rob Summers was the first to receive the stimulator and eventually was able to stand on his own for short periods of time.
"Being able to move my toes, ankles, knees on command, it was absolutely incredible," Summers says. "There are not enough words to describe how I felt. At one point it was just a dream, and now it's reality."
Now three years later the success goes further.
The men are regaining muscle mass and are recovering other functions otherwise lost to their injuries, including sexual function and bladder control.
Nearly 6 million Americans live with paralysis; more than 1 million of them have spinal cord injuries.