The present invention relates to artificial limbs generally and joints for same. The present invention provides hydraulic functional units whereby enabling movement of artificial joints to closely correspond with natural human movement. In the provision of realistic joints, as used in prosthetic limbs, an important aspect in achieving realistic movement is providing a different operating characteristic to the joint when under load. One important characteristic of an artificial leg for achieving a natural-looking walking gait corresponding with those of a stabilized knee, i.e. a knee resisting flexion when under load, is when it bears at least some of the weight of the amputee. Properties of resilient mechanical members are utilized to enable a hydro-mechanical system to be controlled so that it releases a low joint resistance mode relative to a default high resistance mode. The invention also permits alternative embodiments such as electronic, electro fluidic or electromechanical means.