Send a hundred random forty-year-olds for back MRIs. Around sixty come back showing disc bulges, joint changes, or signs of degeneration. Most of those sixty have no back pain. Their backs are doing fine.
The imaging doesn't tell you whose back actually hurts.
So if discs and joints aren't reliably the source, what is?
A lot of the time, it's a muscle on the side of the low back that you've never named, and a muscle in your hip that you've never thought about. Both of them refer pain into the lumbar region in patterns that get diagnosed as disc pain, sacroiliac pain, or just "low back pain, unspecified." Imaging won't show them because muscles don't show up on MRIs the way bones and discs do. They have to be palpated, and the pattern has to be recognized.
This is part of a series on referred pain. A tight muscle doesn't always hurt where the muscle is. Low back pain is the clearest example, and also the complaint that brings more people in for bodywork than any other. Three muscles do most of the work behind a typical episode, and once you can name them, the story usually starts to make sense.
Quadratus lumborum, usually called QL. It runs from your lowest rib down to the back of your pelvis, lateral to the spine on either side. When it shortens or spasms, the ache is deep, on the side of the low back, often described as the lowest of the low, at the line where the back meets the top of the hip. This is the muscle people mean when they say they threw their back out.
Gluteus medius. Higher in the side of the hip than people think. The glute most often involved in low back pain. Refers across the lumbar region and along the iliac crest. The simplest test in the body: lie on your back, put a tennis ball under the back-pocket area, breathe. If it lights up, this muscle is most of your story.
Iliopsoas. Two muscles, usually treated as one. The psoas runs from inside your lower spine, through the pelvis, down to attach near the top of the thigh. When it shortens (and it shortens, in everyone who sits for a living), it pulls forward on the front of the lumbar vertebrae and refers pain vertically along the back. The pain shows up in the back. The muscle lives in the front.
A note on order. I'll often start with glute medius even when the pain is in the back, because it's the most approachable, and the response to it tells me whether the QL is also tight or whether it's just doing its job and bracing against the locked glute. The deeper muscles are reached through the more superficial ones. Layered work, in sequence.
Two things to try this week.
Knee-to-chest, then both knees. Lie on your back. Pull one knee gently toward your chest with both hands. Thirty seconds. Switch. Then both together for thirty seconds more. This decompresses the lumbar spine without compressing it sideways, which most low back stretches accidentally do. It's one of the only stretches that reaches the deep low back safely.
Stand more. If you sit for work, the single biggest favor you can do your low back isn't a stretch and isn't a session. It's interrupting the position. Forty-five minutes sitting, two minutes standing. Repeat. The QL and the psoas are both fed by long stretches of immobility, and they let go fast once you stop feeding them.
When to bring in a professional.
A bodyworker, if the pattern matches and there's no acute injury. Low back referral is textbook and responds well to manual work.
A physical therapist, if the pain doesn't shift after a few weeks of self-care and bodywork, if there's weakness in a leg, or if movement feels unstable in specific positions.
A doctor, immediately, if any of the following: pain radiating down a leg below the knee with numbness or tingling, weakness in a foot, loss of bladder or bowel control, fever with back pain, a recent fall or trauma, or unexplained weight loss alongside the pain. Those are signs of something other than a muscle.
Imaging tells you what's there. It doesn't tell you what hurts. The muscles around the structure are usually the ones with something to say. Listen to the muscles first. If they aren't the answer, look further.