YOU'RE ON CAMERA FOR HOURS. YOUR CHAIR SHOULD WORK AS HARD AS YOU DO

What the research says

1. Twenty people typing for fifteen minutes per posture. With the seat inclined forward, electrical activity in the back muscles was significantly lower than on a flat seat. This is the closest thing to a direct measurement of what a forward-tilted seat does to the load on your back. Soderberg, Blanco, Cosentino & Kurdelmeier (1986). An EMG Analysis of Posterior Trunk Musculature during Flat and Anteriorly Inclined Sitting. Human Factors 28(4), 483–491.
2. Conventional seating is built assuming you can bend about 90 degrees at the hip. Most people have closer to 60. The missing thirty degrees get taken out of the lumbar spine instead, which is why a flat seat rounds your lower back whether or not you are paying attention to it. Mandal (1981). The seated man (Homo Sedens): the seated work position. Applied Ergonomics 12(1), 19–26.
3. A sloping chair produced less trunk flexion, and a sloping work surface less neck flexion, than conventional furniture. Worth reading honestly: the author described the differences as small. Bridger (1988). Postural Adaptations to a Sloping Chair and Work Surface. Human Factors 30(2).
4. The study that disagrees with us, included because you should have it. A 15 degree sloping seat produced no significant improvement in head, trunk or pelvic position, and raised thigh and calf muscle activity by 1.5 to 2.5 times. Two things are worth holding alongside it. Lumbar back-muscle activity still fell, which is the same direction Soderberg measured, so the finding the chair rests on survives its own counter-evidence. And the rig was a bare sloped seat — twelve young men, a reading task, no backrest, nothing under the feet. A slope with nowhere to brace pushes load into the legs, which is exactly what this study measured and exactly what a footring and a backrest that stays in contact are for. Read straight, it says tilt alone is not the answer. We agree; that is why the chair is not just a tilt. Hamaoui, Hassaïne & Zanone (2015). Sitting on a Sloping Seat Does Not Reduce the Strain Sustained by the Postural Chain. PLOS ONE 10(1): e0116353.
5. Pressure measured directly inside a lumbar disc came out at roughly 0.46 MPa sitting against 0.5 standing — sitting slightly lower, not higher. If you have read that sitting loads your spine far more than standing, that came from older measurements this study revised. What did hold up: muscle activity raises disc pressure, and changing position regularly matters for getting fluid and nutrients into the disc. Wilke, Neef, Caimi, Hoogland & Claes (1999). New in vivo measurements of pressures in the intervertebral disc in daily life. Spine 24(8), 755–762.