http://www.foxnews.com/story/0,2933,191827,00.html
http://www.engadget.com/2006/04/17/nanogenerators-turn-you-into-a-duracell/
The devices mentioned in here can apparently be implanted into the human body and convert the kenetic energy into electricity. While engadget replies has many comments on the matrix as a result it could power wearable items, medical devices and perhaps artificial limbs.