[Movements of the lumbar spine. A biomechanical study].

The lumbar spine presents movements of flexion-extension, lateral inflexions and rotations, which are, in fact, the result of movements within each mobile spinal segment. These mobile segments present six levels of freedom corresponding to translation and rotation movements in the three spacial planes. Lumbar mobility decreases markedly with age. Muscles not only participate in the movement itself, but also in its control and in maintaining spinal stability. Their action also depends on the effect of gravity. The authors report various studies concerning spinal stresses during varied movements and positions. Flexion of the trunk is the most stressing; walking, rotations and lateral inflexions increase only moderately the intradiscal pressure. All of the these results concur with the classic ergonomic notions.