Okay, let's move to the back of the pelvis and find your posterior superior iliac spines (PSISs). If you walk your hands up to the top of your iliac crests (remember those sassy hands on hips) and then follow the crest towards the back, they slope down and together. You might feel two little dimples (aka the sacroiliac joints, or SI for short). In very close proximity to the SI joints are the posterior superior iliac spines (PSISs). The PSIS are far less prominent than the ASISs on the front of the pelvis, but provide a more precise way to check the levelness of your pelvis. Instructors might get a bit handsy with your pelvis when first working with you as it helps us better understand what's going on with your body.