Researchers at the University of Tokyo have created a "magic mirror" that allows you to visualize your muscular activity in real time. Using computers and sensors, it shows you visually just how hard your muscles are working while you exercise.

The system, which is currently capable of monitoring the activity of 30% of the body's roughly 300 skeletal muscles, consists of 16 electromyographs (instruments that record the electrical waves associated with muscle activity) attached to the user's body, 10 motion-capture cameras, and a pair of floor sensors to measure the force exerted on the legs.

Robot Watch, Via Pink Tentacle