Final answer:
During SBS flexion, the dura tightens and causes a pulling force on the sacral base, potentially affecting the alignment and mobility of the sacrum.
Step-by-step explanation:
During SBS flexion, the dura and sacral base undergo specific changes. The dura refers to the tough protective membrane that surrounds the spinal cord and extends to the sacrum. When the skull moves into flexion, the dura tightens and causes a pulling force on the sacral base. This tension can affect the alignment and mobility of the sacrum and may contribute to pelvic imbalances.