Chair for the sitting of a user

A chair for the sitting of a user, said chair comprising:

• a support structure (2), which is intended to be placed on the ground and to support a user in a seated position;
• a backrest (3), which is hinged to said support structure (2), around a first hinging axis (R), and is reclinable around said first hinging axis (R) between an inoperative position (A) and at least one reclined position (B);
• an elastic return system (4) comprising a spring (40), which extends between a first end (40′) mechanically connected to said backrest (3) and a second end (40″) mechanically connected to said support structure (2);
• said spring (40) being arranged to be tensioned, at said first end (40′), along a tensioning direction (T) in a first direction (V1), following a movement of said backrest (3), and to exert a corresponding elastic return force, for returning said backrest (3) from said at least one reclined position (B) to said inoperative position (A);
• an adjustment device (5), which is mechanically connected to said backrest (3) and to said support structure (2), is adapted to adjust the corresponding elastic return force exerted by said spring (40), and comprises an actuation system (6), which is mechanically connected to said backrest (3) and is removably connectable to the second end (40″) of said spring (40);
• said actuation system (6) being configured to tension, following the movement of said backrest (3), said spring (40) at said second end (40″) along said tensioning direction (T) in a second direction (V2) opposite said first direction (V1), to increase the corresponding elastic return force exerted by said spring (40) due to the movement of said backrest (3) from said inoperative position (A) towards said at least one reclined position (B).