A bag comprising at least one shoulder strap (11a, 11b) adapted, in use, to be installed at the level of a shoulder (ED, EG) of a wearer, in which: - a shaping frame equipped with said shoulder strap (11a, 11b), wherein said shaping frame has elastic properties such that it deforms elastically with a spring effect when said shoulder strap equipped with said shaping frame is installed on a shoulder ( ED, EG) of the wearer, - the shaping frame has a curved upper portion which is located, in use, at the level of the shoulder (ED, EG) on which said shoulder strap (11a, 11b) is installed, - the curved upper portion is extended downwards by a front longitudinal portion extending, in use, downwards from the trunk of the wearer, from the ventral face of said wearer, - the front longitudinal portion is shaped so that, in use, it presses against a first region of the trunk of the wearer other than the shoulder (ED, EG) on which said shoulder strap (11a, 11b) is installed, - the curved upper portion further extends by a rear longitudinal portion extending, in use, towards the bottom of the trunk of the wearer, from the dorsal face of said wearer, so that the shaping frame has a general shape of an arch or a horseshoe, - the rear longitudinal portion is shaped so that, in use, it presses against a second region of the trunk of the wearer other than the shoulder (ED, EG), which second region is distinct from the first region, which second region is a dorsal region of said wearer or a lateral flank of said wearer, characterized in that: - the rear longitudinal portion comprises a segment which is twisted around the longitudinal axis (Ab) of said rear longitudinal portion, so that said rear longitudinal portion has a support face which, in use, is oriented parallel to the second support region of the trunk of the wearer. - a shaping frame equipped with said shoulder strap (11a, 11b), wherein said shaping frame has elastic properties such that it deforms elastically with a spring effect when said shoulder strap equipped with said shaping frame is installed on a shoulder ( ED, EG) of the wearer, - the shaping frame has a curved upper portion which is located, in use, at the level of the shoulder (ED, EG) on which said shoulder strap (11a, 11b) is installed, - the curved upper portion is extended downwards by a front longitudinal portion extending, in use, downwards from the trunk of the wearer, from the ventral face of said wearer, - the front longitudinal portion is shaped so that, in use, it presses against a first region of the trunk of the wearer other than the shoulder (ED, EG) on which said shoulder strap (11a, 11b) is installed, - the curved upper portion further extends by a rear longitudinal portion extending, in use, towards the bottom of the trunk of the wearer, from the dorsal face of said wearer, so that the shaping frame has a general shape of an arch or a horseshoe, - the rear longitudinal portion is shaped so that, in use, it presses against a second region of the trunk of the wearer other than the shoulder (ED, EG), which second region is distinct from the first region, which second region is a dorsal region of said wearer or a lateral flank of said wearer, - the rear longitudinal portion comprises a segment which is twisted around the longitudinal axis (Ab) of said rear longitudinal portion, so that said rear longitudinal portion has a support face which, in use, is oriented parallel to the second support region of the trunk of the wearer.