CrossFlowV: SI Love. 53 minutes. Pain in your lower back and / or pelvic area? Show your SI (sacroiliac joint - links the pelvis and lower spine) some love with this flow. Open your hips, create space in your spine, and then strengthen your core, glutes, and surrounding muscles to stabilize. Grab a yoga block if you have one, and be prepared to feel SO much better after you are done! Deep breaths, and feel GREAT!