A study published in the European Spine Journal involved 18 patients with non-specific chronic low back pain and 19 healthy individuals without back pain; participants sat for 30 minutes on a sofa with a seat height of 40 cm and a seat depth of 50 cm, lacking additional lumbar support. The results showed that, over the course of sitting, the pelvises of both groups gradually tilted backward; notably, among patients with chronic back pain, those who experienced a more pronounced posterior pelvic tilt also reported a more significant increase in pain.
As the buttocks sink lower, the pelvis tends to tilt backward and the body slides forward, shifting the alignment intended to support the lower back. This results in a posture where the upper back rests against the backrest while the buttocks slide forward, causing the lower back to curve into a “C” shape. While this position may feel comfortable initially, prolonged sitting can lead to lower back discomfort.