In one aspect, the invention provides methods and apparatus facilitating an adjustable-stiffness prosthesis or orthosis (including approximations to arbitrarily definable non-linear spring functions). Spring rates may be varied under no-load conditions during a walking gate cycle to minimize power consumption....http://www.google.fr/patents/US20040064195?utm_source=gb-gplus-shareBrevet US20040064195 - Variable-mechanical-impedance artificial legs
