I would like to offer comment that the important thing is spinal mobility, in all directions, and then stability and endurance (strength) thoughout that range of that mobility.

The concept (verbalisation) of sitting tall can lead to increased tension in the shoulders, whereas the maintenance of the correct pelvis position will help establish the right thoracolumbar curve and therefore balance the head and shoulders on the trunk. This of course all relies on having the mobility and strength to achieve an optimal balance of all the spinal curves.

I tend to look at spinal mobility first and only advise the individual to correct within their limitations. If they lack spinal extension (mobility), expecially in the thoracolumbar junction then I work to achieve more movement and awareness of that area of the body. As they become more mobile then their ideal sitting posture should continue to change (usually a lengthening of the spine and a return to a more s-shaped spine rather than acute angles at lumbosacral, cervicothoracic and upper cervical junctions. Hope this makes sense? 8o