Next, using various measures, the researchers compared optically induced muscle contractions with those induced by the electrical cuff. Small, slow-twitch muscle fibers were activated at the lowest levels of optical stimulation. But with electrical stimulation, bigger fibers were triggered first. What's more, optically triggered contractions were sustained far longer than those produced by electrical stimulation.
"With optical stimulation, the muscles retained about one-third of their initial maximum force after 20 minutes, and remained at that plateau for quite a while afterward," said Llewellyn, who is now finishing his work on an MD at Stanford. "Electrical stimulation completely exhausted the same muscles within four minutes." Consistent with this, optical stimulation initiated contractions much more easily in muscles composed of predominantly slow-twitch fibers than in muscles richer in fast-twitch fibers. Electrical stimulation, in contrast, induced contractions equally in both muscle types.
The approach is, for now, primarily a research tool, Delp said. But it holds promise for clinical applications in the longer term if a way can be found to safely introduce genes coding for light-sensitive nerve-cell-surface proteins into people, he said. Just as techniques now use electrical cuffs to get paraplegics to walk for a
|Contact: Bruce Goldman|
Stanford University Medical Center