The invention relates to a leg unit (12a, 12'a； 12b, 12'b) for a wearable sitting posture assisting device (10a), comprising an upper support (13a； 13b) designed to receive a weight force of a person (11 a), a lower support (14a； 14b) designed to transmit the person's (11 a) weight force to a ground (15a), a joint (16a； 16b) connecting the at least two supports (13a, 14a； 13b, 14b) to each other, and a blocking means (17a； 17b) implementing a blocked state to block the joint (16a； 16b) at at least one sitting angle (21 a； 21 b) corresponding to an at least partly sitting posture, and comprising a guiding means (29a； 29b) for the blocking means (17a； 17b), which guiding means (29a； 29b) is designed to allow a rotation of the joint (16a； 16b) while the blocking means (17a； 17b) is in the blocked state, to a wearable sitting posture assisting device (10a), comprising two of these leg units (12a, 12'a； 12b, 12'b), and to a method to block such a wearable sitting posture assisting device (10a) in an at least partly sitting posture.
