Flexor is an arm sleeve with a bend sensor, an annunciator, and electro-luminescent lights. It keeps track of arm movement and uses models of arm motion to create entertaining and useful feedback for physical therapy or exercise. If you move your arm in natural gestures, the electro-luminescent lights sparkle like sequins with every movement. When you bend your arm for exercise, as in a weight-lifting bicep curl, the sleeve counts repetitions, encouraging body awareness. A variable resistor in the sleeve senses body position, while an on-board microprocessor facilitates interaction through electro-luminescence and sound. Therapy can also be coupled with expression, communication, performance, play, jewelry, and tools. This playful exploration could also be used to teach people how to protect their ligaments and muscles from strain and injury while playing tennis, squash, or golf, or even picking up their small children.