David Mzee broke his neck in 2010. He was a college student in Zurich at the time, an athlete who enjoyed risk and contact, and he flipped off a trampoline and onto a foam pad. “The foam pad, it didn’t do its job,” he said.

Mr. Mzee, now 33, is one of three men who lost the use of their legs years ago after severe spinal injuries, but who now are able to walk without any supports, if briefly and awkwardly, with the help of a pacemaker-like implant, scientists reported on Wednesday.

The breakthrough is the latest achievement in the scientific effort to understand and treat such life-changing injuries. Several recent studies have restored motion to paralyzed or partly paralyzed patients by applying continuous electrical stimulation to the spinal cord.

The new report, described in the journal Nature, is the first demonstration of so-called patterned stimulation: An implant sends bursts of targeted stimulation to the muscles that intend to move. In effect, the stimulation occurs on an as-needed basis, roughly mimicking the body’s own signaling mechanism.