The spine is flexible enough to allow fluid movements in certain directions, such as flexion (bending forwards), extension (bending backwards), lateral flexion (side bending) and rotation (twisting). The structure of the vertebrae naturally restricts the range of movement (ROM) of the spine. Many movement patterns need an erect posture or spinal stability: for example, when reaching up to lift down a heavy item, or to achieve a good gait (walking pattern).