Тype of posture where the subject’s lower spine curves forwards(lumbar hypolordosis) instead of natural arching, while also rotating pelvis up(posterior pelvic tilt). Hips are usually pushed in front of the line of the shoulders. Often occur when a character leaning back against something, or with hip focus to amplify accent on person's nether regions.
Not to be confused with arched back(hyperlordosis), when spine is arched in similar manner, but pelvis tilted down and butt is noticeably sticking out. And also contrapposto(with frontal pelvic tilt).
Defining feature of swayback posture is posterior pelvic tilt.
It is intended to be used only when character is standing or kneeling. When character is lying use arched back or body bridge if applicable.