Most people think of back muscles as simple “cables” that pull us upright. But during my PhD research at the University of Toronto, I learned the lumbar multifidus is something much more important: a layered support system designed to protect the spine segment by segment.
Using microdissection and 3D modelling, I digitized over a thousand individual muscle fiber bundles per specimen and found the multifidus isn’t one uniform muscle. It has distinct layers with different jobs: the more superficial fibers help generate movement, while the deeper fibers are built for fine control, stability, and proprioception.
One finding stood out: at L5 (the level where disc injuries most often occur), the intermediate layer is absent. That means the lowest lumbar segment is missing an entire stabilizing layer, which likely helps explain why L5 is such a common “weak link” in back pain and instability. Three-Dimensional Study of the …
Here’s why this matters clinically: after back pain, these deep stabilizers often “shut down” and don’t automatically switch back on. If rehab focuses only on general strengthening, you can train the big “mover” muscles while the deep protective system stays underactive.
At Body In Balance Physiotherapy, we don’t do generic programs. We assess which segments aren’t stabilizing, retrain the deep support system first, and then build strength and capacity on top of it. This means you don’t just feel better; you move better and stay better as well.