TECH - Mechanical energy converted to Electrical "Reverse electrowetting" Taylor and Krupenkin - Wisconsin - micro-fluidic nano device - Human Gait to Power Portable Electronics

Energy produced by humans during walking, which is normally lost as heat, converted into up to 20 watts of electrical power that can be used to power mobile electronic devices.An energy-harvesting technology that promises to dramatically reduce our dependence on batteries and instead capture the energy of human motion to power portable electronics.
http://www.sciencedaily.com/releases/2011/08/110823115139.htm

"Humans, generally speaking, are very powerful energy-producing machines," "While sprinting, a person can produce as much as a kilowatt of power."