Chair for the sitting of a user

Chair for the sitting of a user, in particular office chair, which comprises:

• a support structure (2), intended to be abutted against the ground;
• a seat (3), mounted on said support structure (2) and provided with an upper face (30), intended to receive a user in seated position, and with an opposite lower face (31), intended to be directed towards the floor;
• a flexible covering element (4), placed to cover at least the upper face (30) of said seat (3) and provided with a main portion (40);
• a flexible tensioning element (5), which is engaged with the main portion (40) of said covering element (4) and is provided with a grip portion (50);
• a traction element (6), which is mechanically connected to the grip portion (50) of said tensioning element (5), is rotatably mounted on the lower face (31) of said seat (3) and rotatable around a rotation axis (R) in a tensioning sense (T), in order to at least partially enclose said tensioning element (5) on said traction element (6) and tension said covering element (4) to enclose said seat (3);
• in which said traction element (6) is provided with a perimeter toothing (610), configured in order to be coupled to said seat (3), in order to block said traction element (6) in position, preventing the rotation thereof around said rotation axis (R), in a blocking sense (B), opposite said tensioning sense (T);
• said chair (1) being characterized in that said seat (3) comprises a flexible blocking lever (7), which is extended in a single body starting from the lower face (31) of said seat (3), starting from a first end (7′), connected to the lower face (31) of said seat (3), up to a second free end (7″), at which said blocking lever (7) is provided with a coupling portion (70);
• in which the first end (7′) of said blocking lever (7) defines a rotation pivot (F) of said blocking lever (7), and in which said blocking lever (7) is elastically movable, around said rotation pivot (F), between an engagement position, in which said coupling portion (70) is engaged with the perimeter toothing (610) of said traction element (6), in order to prevent the rotation of said traction element (6) around said rotation axis (R), in said blocking sense (B), and a release position, in which said coupling portion (70) is disengaged from the perimeter toothing (610) of said traction element (6), in order to allow the free rotation of said traction element (6) around said rotation axis (R).