Center of Gravity
The point where all your mass is balanced; located in front of and near the top of the sacrum, approximately at the level of the second sacral vertebra.
Sacrum
The triangular bone at the base of the spine; made of five fused vertebrae; wedged between the two ilia; transfers upper body weight to the pelvis and legs.
Sacroiliac (SI) Joint
The joint where the sacrum and ilium articulate on each side; transfers weight from upper body to lower body; allows minimal movement (2-4 degrees); has two joints (left and right).
Nutation
The movement at the SI joint where the top of the sacrum tilts forward and down; happens during forward bending or weight-bearing.
Counternutation
The movement at the SI joint where the top of the sacrum tilts backward and up; happens during backbending or leg lifting.
ASIS (Anterior Superior Iliac Spine)
The bony prominences at the front of the hips on either side; the sharp points at the front of the iliac crests; crucial alignment reference points.
AIIS (Anterior Inferior Iliac Spine)
The bumps below the ASIS on the front of the pelvis; where the rectus femoris attaches.
PSIS (Posterior Superior Iliac Spine)
The bony prominences at the back of the pelvis—the ‘dimples’ in the lower back on either side of the sacrum; commonly mistaken for the SI joints themselves.
Ischial Tuberosities
The sitting bones; the lowest, most posterior points of the ischium; what you actually sit on.
Anterior Pelvic Tilt
Pelvic movement where the front hip bones (ASIS) tilt forward and down, sitting bones tilt backward and up; tailbone sticks out; increases lumbar lordosis; natural in backbends.
Posterior Pelvic Tilt
Pelvic movement where the front hip bones (ASIS) tilt backward and up, sitting bones tilt forward and down; tailbone tucks under; flattens lumbar curve; natural in forward folds.
Hip Hiking
Pelvic movement where one side of the pelvis lifts up toward the ribcage while the other drops; lateral pelvic tilt; should be avoided in standing poses.
Pelvic Rotation
Pelvic movement where it rotates around a vertical axis; one ASIS rotates forward while the other rotates backward; happens in twists and asymmetrical poses.
Pelvic Floor
The complex system of muscles, fascia, and ligaments forming a hammock-like structure at the bottom of the pelvis; includes perineal muscles, levator ani, and pubococcygeal muscles.
Perineal Muscles
The superficial layer of pelvic floor muscles; involved in sexual function and continence.
Levator Ani
The main supportive layer of the pelvic floor; a broad muscle group forming the floor of the pelvis; includes pubococcygeus, puborectalis, and iliococcygeus.
Pubic Symphysis
The cartilaginous joint where the two pubic bones meet at the front-center of the pelvis; an amphiarthrotic joint with slight movement.
