A method for articulating a leg prosthesis, comprising: - an element intended to be secured to the thigh of a subject; - another element (4, 14) intended to be secured to the leg of the prosthesis, this other element comprising a body and a tilting plate articulated on this body at an axis offset towards the front in the direction of walking, this other element (4, 14) being intended to be secured to the leg of the prosthesis by the tilting plate; - an inner ring carried by one of the elements and an outer ring carried by the other element; - the rings being rotationally coupled by means of a wedging clutch (7, 8, 8a) interposed between them and provided with a means (9, 10, 11) for neutralising the coupling of the two rings and comprising a control wheel: - this control wheel being coupled, by slip-free winding, to at least one link for locating the wheel in one or other of two positions thereof with respect to the clutch; - one end of this link being fixed to the element secured to the leg by an elastic fixing acting on this link in the direction of release of the clutch; - the other end of this link being fixed to the tilting plate by means of a return roller carried by the body, so that the elastic fixing of the link tends to separate the plate from the body and so that the folding of the plate against the body acts on the link counter to its elastic return in order to lock the clutch; - so that a pressing on the ground at the heel of the foot extending the leg tends to fold the plate in order to lock the articulation, and so that a pressing on the ground at the tip of the foot tends to move the plate away in order to unlock the articulation. - an element intended to be secured to the thigh of a subject; - another element (4, 14) intended to be secured to the leg of the prosthesis, this other element comprising a body and a tilting plate articulated on this body at an axis offset towards the front in the direction of walking, this other element (4, 14) being intended to be secured to the leg of the prosthesis by the tilting plate; - an inner ring carried by one of the elements and an outer ring carried by the other element; - the rings being rotationally coupled by means of a wedging clutch (7, 8, 8a) interposed between them and provided with a means (9, 10, 11) for neutralising the coupling of the two rings and comprising a control wheel: - this control wheel being coupled, by slip-free winding, to at least one link for locating the wheel in one or other of two positions thereof with respect to the clutch; - one end of this link being fixed to the element secured to the leg by an elastic fixing acting on this link in the direction of release of the clutch; - the other end of this link being fixed to the tilting plate by means of a return roller carried by the body, so that the elastic fixing of the link tends to separate the plate from the body and so that the folding of the plate against the body acts on the link counter to its elastic return in order to lock the clutch; - so that a pressing on the ground at the heel of the foot extending the leg tends to fold the plate in order to lock the articulation, and so that a pressing on the ground at the tip of the foot tends to move the plate away in order to unlock the articulation.