chuan calls for adjusting the lower back curvature (as well as the rest of the spinal curvatures) through specific re-alignments of the pelvis to the thighs, it's referred to in shorthand as 'dropping the tailbone'. The specifics of the structural change are school specific, and are part of the jibengong (essential technique) of these schools. The adjustment is referred to in tai chi chuan literature as 'when the lowest vertebrae are plumb erect...' See also Hyperkyphosis Kyphoscoliosis Lordosis behavior Pott's disease Footnotes References External links What is Lordosis? Lordosis - MedlinePlus definition Lordosis - SpineUniverse Ways To Treat Lordosis Human back Deforming dorsopathies Congenital disorders of musculoskeletal system Symptoms and signs: musculoskeletal system