Comment Re:"Unpowered" (Score 4, Informative) 128
The energy to load the spring comes from the user as part of the normal operation cycle. That makes it unpowered.It does not bring extra energy to the operation (user walking by converting chemical energy to muscle contraction), it only changes how the energy is used.
The trick is to define the system and timeframe you are looking at sensibly. In this case you have the braces and the user taking a number of steps. The user generates the power, the braces are unpowered. If you looked at the braces for one unloading of the spring, you could say the frame is powered by the spring, but that is not very useful choice in most contexts outside design of the device.