Prosthesis uses swinging arms to tell legs when to step

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 The natural motion of swinging one’s arms may someday drive the movement of paralyzed legs. A device, described in the Aug. 13 Journal of Neuroscience, creates an artificial connection between arms and legs that could bypass sites of spinal damage.

In an experiment, 10 healthy male participants lay on their sides while wires supported their legs’ weight and held them horizontal, a low-friction setup that allowed scientists to see subtle movements. The prosthesis consisted of several components that span the body: Electrodes detected activity in shoulder muscles as the men swung their arms. These signals were then converted by a computer into stimulations ultimately delivered to the spine and a nerve near the ankle. Researchers asked the men to relax their legs, allowing their legs to become puppets controlled by the stimulation.

When the men swung their arms, their legs immediately started a walking motion, Syusaku Sasada of the National Institutes of Natural Sciences in Okazaki, Japan, and colleagues report. The legs sped up when the men pumped their arms faster and then gradually stopped when the men rested their arms or the device was turned off. In separate experiments, finger movements also triggered walking.