Back pain that worsens through a rehearsal, makes you shift constantly in your chair, or forces you to stand between movements is one of the most disruptive injuries a musician can experience — and one of the most misunderstood. Two of the most common culprits, lumbar disc herniation and lumbar segmental instability, look similar from the outside but behave very differently and require entirely different treatment approaches. In this post, I break down the mechanics behind each, how to recognize which one you might be dealing with, and what physical therapy can do to get you back to playing comfortably.