A rear portion of a ski mountaineering binding, wherein: it comprises a base (2, 3) which is fixable to a ski; it comprises a turret (5, 6) which is borne by the base (2, 3) and which is rotatable with respect to the base (2, 3) in order to assume a first turret position, wherein it is fixable to the heel of a ski boot, so that it is possible to ski downhill, and in order to assume a second turret position, wherein it is not fixable to the heel of a ski boot, so that it is possible to walk uphill; it comprises a brake (8, 81, 82, 83, 84, 85, 86, 87, 88, 89) for a ski; the brake (8, 81, 82, 83, 84, 85, 86, 87, 88, 89) comprises a braking lever which is rotatable to assume a braking position, in which it can brake a ski when the base (2, 3) is fixed to the ski, and a non-active position, in which it is non-active; the brake (8, 81, 82, 83, 84, 85, 86, 87, 88, 89) comprises first elastic means for rotating the braking lever towards the braking position; the braking lever is arranged so as to be pressable by the heel of the ski boot, when the base (2, 3) is fixed to the ski and the turret (5, 6) is in the first turret position, in order to reach the non-active position against the action of the first elastic means; characterised in that: it comprises a rotation member which is rotatingly borne by the base (2, 3) and which in turn bears the braking lever so that a rotation of the rotation member corresponds to a rotation of the braking lever, and vice versa; it comprises connecting means (31, 32, 33, 35, 37) which connect the rotation member and the turret (5, 6) to one another, in such a way that the rotation member and the turret (5, 6) are solidly constrained to one another, when the turret (5, 6) is in the second turret position and when the braking lever is in the non-active position, so that it is possible to walk uphill. it comprises a base (2, 3) which is fixable to a ski; it comprises a turret (5, 6) which is borne by the base (2, 3) and which is rotatable with respect to the base (2, 3) in order to assume a first turret position, wherein it is fixable to the heel of a ski boot, so that it is possible to ski downhill, and in order to assume a second turret position, wherein it is not fixable to the heel of a ski boot, so that it is possible to walk uphill; it comprises a brake (8, 81, 82, 83, 84, 85, 86, 87, 88, 89) for a ski; the brake (8, 81, 82, 83, 84, 85, 86, 87, 88, 89) comprises a braking lever which is rotatable to assume a braking position, in which it can brake a ski when the base (2, 3) is fixed to the ski, and a non-active position, in which it is non-active; the brake (8, 81, 82, 83, 84, 85, 86, 87, 88, 89) comprises first elastic means for rotating the braking lever towards the braking position; the braking lever is arranged so as to be pressable by the heel of the ski boot, when the base (2, 3) is fixed to the ski and the turret (5, 6) is in the first turret position, in order to reach the non-active position against the action of the first elastic means; characterised in that: it comprises a rotation member which is rotatingly borne by the base (2, 3) and which in turn bears the braking lever so that a rotation of the rotation member corresponds to a rotation of the braking lever, and vice versa; it comprises connecting means (31, 32, 33, 35, 37) which connect the rotation member and the turret (5, 6) to one another, in such a way that the rotation member and the turret (5, 6) are solidly constrained to one another, when the turret (5, 6) is in the second turret position and when the braking lever is in the non-active position, so that it is possible to walk uphill. it comprises a rotation member which is rotatingly borne by the base (2, 3) and which in turn bears the braking lever so that a rotation of the rotation member corresponds to a rotation of the braking lever, and vice versa; it comprises connecting means (31, 32, 33, 35, 37) which connect the rotation member and the turret (5, 6) to one another, in such a way that the rotation member and the turret (5, 6) are solidly constrained to one another, when the turret (5, 6) is in the second turret position and when the braking lever is in the non-active position, so that it is possible to walk uphill.