But the biggest benefit he's seen is a surprising one. “You have to learn how to use those muscles again,” says Olafsson. “How to tighten them up, in front and back. And that's the main thing. Those muscles start getting bigger, so you get better at walking. I have more stamina. My gait is better. I don't limp as much.” By forcing the wearer to actively use muscles that were previously ignored, sensor-connected limbs could halt or reverse their deterioration. It's a reminder that, despite the urge among the able-bodied to obsess over cybernetic enhancements, bionic limbs are chiefly medical devices for now, designed to restore function. That a brain-controlled bionic leg would also promote muscle growth is stranger, and more exciting, than all of the superpowered cyborgs that science fiction has to offer.