During spinal flexion, what happens to the annulus fibers?

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Flexion loads the disc so that the front gets squeezed while the back is pulled taut. The annulus fibrosus is made of concentric layers of collagen fibers oriented obliquely to resist twisting and bending. When you bend forward, the vertebral bodies move closer at the front, compressing the anterior portion of the disc. At the same time, the posterior portion resists the bending by being stretched, placing the posterior annulus under tensile load. This pattern—anterior compression with posterior tension—fits how the disc’s fiber architecture responds to forward bending. For contrast, extension would reverse the pattern, with posterior compression and anterior tension, while no change would not reflect the loading that occurs with real bending movements.