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The influence of backrest inclination and lumbar support on the shape of the lumbar spine in sitting positions has been studied radiographically on 38 healthy subjects. Four angles of backrest inclination and four different sizes of lumbar support were studied. In addition, the lumbar support was placed at three different lumbar levels. When sitting down from a standing position, the pelvis rotates and the lumbar lordosis decreases. Increases in the backrest-seat angle had only minor effect on the lumbar lordosis. A lumbar support, on the other hand, had a significant influence: the lordosis increased with increasing support. The location of the lumbar support with respect to the level of the spine did not significantly influence the measured angles.
Andersson et al. (1979) studied this question.