One of the most common areas people try to self-treat is the lower back. This is either done with something like a lacrosse ball or a two tennis balls taped together. But this can do more harm than good.
If your lower back keeps getting irritated, it’s most likely a lack of stability rather than a lack of mobility. One of the most effective ways to create stability through the pillar (shoulders, hips, core) and maintain long-term movement pattern reeducation, is through this plank progression.
Check out this plank series that includes the RKC plank and side plank which increase stability through the four layers of the abs, iliopsoas, lateral hip group and quadratus lumborum. Your lower back will thank you.