A 1.6-kilogram knee brace worn while walking could power portable devices and prosthetic limbs. Developed by researchers at Simon Fraser University, the brace generated about five watts of electricity per person during a recent experiment, enough to run 10 cell phones concurrently. One subject generated 54 watts by running in place. To capture this energy, the brace relies on gears, a clutch, a generator and a computerized control system that monitors the knee's angle to determine when to engage and disengage power generation. The researchers targeted a particular part of the stride: halfway through the swing of the lower leg after it has left the ground through the time the foot returns to the ground. By tapping into unconscious muscle movements, this and other electricity-from-motion devices are more likely to be used. The researchers describe the brace in the February 8 Science.