Abstract: An artificial leg includes a knee mechanism having means for restricting knee flexing movement during the stance phase of the walking cycle. The restricting means includes a piston and cylinder assembly so coupled in the mechanism that the piston is movable in the cylinder with knee flexion and extension. The knee mechanism includes two chassis parts arranged to move relatively to each other when an axial load is applied to the limb. One end of the piston and cylinder assembly is connected to one of the chassis parts while the other chassis part engages a control member coupled to a valve inside the piston and cylinder assembly so that the valve is operated in response to relative load-dependent movements of the chassis parts in order to restrict the flow of fluid and thereby create resistance to knee flexion during the stance phase. The chassis parts are connected together by an anterior pivot joint and are resiliently moveable relative to each other according to applied load.