we have to consider getting people with motor impairment to supine positions?
The chair as a health hazard
The downward gravity force pushes the bottom of the pelvis (sacrum) down and forward. Eventually the sitter finds himself sitting mostly on a crocked pelvis which creates a c-curve slouch. (from The Chair by Galen Cranz). These distortions are not easy to self-restore by a person with movement dysfunction.
Therapeutic Positioning can help counteract these distortions.