Car seat designers attempt to accommodate the average body. Because few people sit with good pelvic support, car seats are molded around the average person’s poor posture. This means that achieving good support in your car requires some ingenuity. Adjust your seat back to be as upright as possible. To sit with a spacious pelvic floor, slide your buttocks as far back as you can into the crack between the backrest and seat. The bottom of the seat back can then support your sacrum.
This arrangement will leave several inches of space between your spin e and the seat back. Insert a cushion or other prop into this space to support your chest. A prop in the lumbar area may be comfortable for some people, although placing it higher place, just below the shoulder blades, will feel better for others. A small bolster filled with buckwheat hulls can be moved up or down to accommodate your spine’s shifting tensions for long drives. When the prop is positioned correctly, your torso should feel taller and more open and your neck should be comfortably centered above your heart. You may find that this thrusts the top of your head nearer to the car’s roof. The next time you buy a car, be sure it fits your best posture. The great height of SUVs, vans, and trucks offers sufficient headroom to allow for sitting with your spine and chest erect.
The height also allows for a more open groin angle. Seats in small cars incline back, compressing the body to fit inside and forcing the chest back and neck forward. Make time to interrupt prolonged sitting, in car or office, with periods of physical activity. For long road trips, add five minutes per hour to your estimated arrival time and stop long enough to work the kinks out of your body. – Excerpt from Mary Bond’s The New Rules of Posture.