The childhood advice of sitting up straight, shoulders back, is incorrect.

Sitting this way takes effort. We end up arching our backs by tensing up our muscles. When we tighten them, we shorten them, and that arches the back, loads the discs in the lower back, and pushes the edges of the vertebrae against each other. Over time, that could alter our anatomy.

If you tend to slump, you need to learn to lengthen your back. Use the time that you're sitting to stretch yourself against the backrest.

• Sit with your bottom well back in your chair while moving your upper body away from the backrest.
• Place your fists on the front lower border of your rib cage, then gently push back on your rib cage so as to elongate your lower back.
• Then, grab some place of your chair and make yourself taller by gently pushing the top of you away from the bottom.
• In that position, put your back against the chair's backrest. Ideally, the chair would have some grippy thing mid-back to hold you.