Technically, we use muscles all the time to control games (and express our anger at them, if you're the gamepad-throwing type), but when's the last time you strapped sensors to your pythons and fist-clenched Mario into stomping goombas? Probably never, unless you're one of the soldering wizards at Advancer Technologies.
Not as high-tech as the infra-red laser of your Xbox 360's Kinect, but there's something oddly alluring about using a childhood's worth of death grip training to order around the world's most fearless plumber. As you can see from the video, getting Mario to move involves twitching one or both biceps, forearms or, for some commands, a combination of them.
Behind the system is a set of electromyographic sensors -- essentially sensors the look out for the electrical signals produced by your muscles. The ones used here were custom-built by Advancer, and the link at the bottom of this article goes to a tutorial on how to build them, if you're keen to construct your own. Not that it's straightforward -- you'll need some experience with soldering, wiring and the ever-flexible Arduino.
Of course, this setup can be used for any game, but a platformer, such as a title from the Super Mario Bros. series, with simple commands -- jump, left, right and crouch -- is a great stomping ground for the technology.
It's certainly not something the average user is going to go out and buy, but the potential to help those with disabilities that make it difficult to interact with computers via traditional means is easy to see.
USB Biofeedback Game Controller [Instructables]