The study's other two participants - Kent Stephenson of Mount Pleasant, Texas and Andrew Meas of Louisville, Kentucky - have had similar results.
"I'm able to (make) these voluntary movements and it really changed my life," Stephenson said. He said the electrical device lets him ride on an off-road utility vehicle all day with his friends and get out of the wheelchair.
"I've seen some benefits of (the device) training even when it's turned off," he added. "There have been huge improvements in bowel, bladder and sexual function."
The new study was paid for by the U.S. National Institutes of Health, the Christopher and Dana Reeve Foundation and others.
Experts said refining the use of electrical stimulators for people with paralysis might eventually prove more effective than standard approaches, including medicines and physical therapy.
"In the next five to 10 years, we may have one of the first therapies that can improve the quality of life for people with a spinal cord injury," said Gregoire Courtine, a paralysis expert at the Swiss Federal Institute of Technology in Lausanne, who was not part of the study.
Ellaway said it was unrealistic to think that paralyzed people would be able to walk after such treatment but it was feasible they might eventually be able to stand unaided or take a few steps.
"The next step will be to see how long this improvement persists or if they will need this implant for the rest of their lives," he said.
The National Institutes of Health is investing in more advanced stimulators that would better target the spinal cord as well as devices that might work on people who are paralyzed in their upper limbs.
