In the early 20th century, sacroiliac joint syndrome (SIJ) was the most common medical diagnosis for low back pain, which resulted in that period being labeled the “Era of the SI Joint.” Any pain emanating from the low back, buttock or adjacent leg usually was branded and treated as SIJ.
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Pelvic floor muscles such as levator ani, coccygeus and obturator internus attach to the front, back and sides of the pelvis and sacrum and form the bottom of the core. These muscles must be able to contract to maintain continence, and to relax allowing for urination and bowel movements, and in women, sexual intercourse.
https://www.youtube.com/embed/ph-B8o1_bo4 From Dynamic Lower Body course Treating Sacroiliac Joint Upslips Although ‘creep’ is an engineering term, it also applies to human tissue…the lumbopelvis in particular.