The short answer
Disc-related pain is usually centered, often worse with sitting, bending or coughing, and may refer into the leg in a defined pattern. Muscular pain is usually to one side, tender to press, worse with specific movements and eased by others. The examination separates them by how symptoms change under repeated movement, not by where they hurt.
- Where it hurts is data, not diagnosis — muscles refer into the leg and discs can hurt only in the back.
- Repeated movement testing is what separates them: symptoms that retreat toward the midline point to a disc mechanism and to the direction of treatment.
- Imaging rarely changes the plan, because disc changes are common in people with no pain at all.
- Saddle numbness, bladder or bowel changes or progressive weakness in both legs are emergency symptoms, not appointment symptoms.
Almost everyone with a sore back has a theory about what it is, and the theory shapes what they do about it. Getting it wrong is expensive in time rather than money: months of stretching something that was never tight, or months of protecting something that needed loading.
Why the location tells you less than you think
Pain is a poor mapmaker. A muscle in the buttock can refer down the leg convincingly enough to be called sciatica for a year, and a disc can produce pain felt entirely in the low back with nothing below it.
So the first thing an examination does is stop treating the location as the answer. Where you feel it is data, not diagnosis.
What separates the two is behavior: what makes it worse, what makes it better, and crucially how it responds to the same movement performed repeatedly.
The history that points toward a disc
Pain that is worse sitting, and worse still getting up from sitting after a while. Worse first thing in the morning, particularly bending to put socks on. Worse with coughing, sneezing or straining, which raise pressure inside the abdomen and therefore inside the disc.
Often central or symmetrically spread across the low back, though not always. Sometimes referring into the buttock, thigh or below the knee in a pattern that follows a nerve rather than wandering.
And a history of it building over hours or a day rather than arriving in a single moment, though a sudden onset while bending and lifting is entirely compatible with a disc too.
The history that points toward muscle or joint
Pain that arrived in a distinct moment, often with a movement you can name. Located to one side. Tender to press on a specific spot, and the pressure reproduces the pain you came in with.
Worse with particular movements and reliably eased by others, without much relationship to sitting time or to coughing.
Often stiff rather than sharp, and typically easier once you have been moving for twenty minutes — a pattern that a disc-driven presentation does not usually follow in the same way.
What repeated movement testing shows
This is the part that does most of the work, and it is why an examination is worth more than a description over the phone.
You perform a movement repeatedly — typically extension or flexion, ten to fifteen times — and we watch what happens to the symptoms. Not just whether it hurts, but whether pain that was in the leg moves toward the back.
Symptoms retreating toward the midline is called centralisation, and it is one of the more useful findings in musculoskeletal practice. It points strongly toward a disc-related mechanism and, more importantly, it tells you which direction the treatment should go.
A muscular problem does not behave that way. It gets more sore with repetition, or less, but it does not migrate.
The neurological screen
If there is any leg symptom, reflexes, strength and sensation get tested in a specific pattern, because nerve roots supply predictable territories.
Weakness of the big toe, a diminished ankle reflex, numbness along the outside of the calf — each points to a particular level. That is not the same as a disc pressing on a nerve, but it changes the picture and it changes how cautiously the plan proceeds.
Straight leg raise and slump testing assess whether the nerve itself is sensitive to being put under tension. A muscular problem does not usually respond to that.
Why the distinction changes the plan
A disc-related presentation that centralises with extension gets loaded in extension, with sitting posture and lifting mechanics addressed, and with progressive loading once symptoms have moved. Aggressive stretching into flexion is often exactly wrong.
A muscular or joint-driven problem responds to manual work, needling into the involved tissue, manipulation of a restricted segment, and loading. Extension protocols are irrelevant to it.
Treat the second as though it were the first and you waste weeks. Treat the first as though it were the second — stretching and massaging a disc-driven back — and you can make it genuinely worse.
The imaging trap
Scans of pain-free adults routinely show disc bulges, degeneration and protrusions, and the proportion rises steadily with age. Finding one on your scan does not establish that it is causing your pain.
Which is why imaging rarely changes the plan for ordinary back pain, and why the guidelines say so. The examination establishes the mechanism; the scan is for answering a specific question that the examination has raised.
There is a whole article on this, because it is the single most common source of unnecessary fear I encounter.
What is neither
Not every back is one of these two. The sacroiliac joint, the hip, and referred pain from abdominal or pelvic structures all present as low back pain.
Stress fractures in the pars region appear in young athletes doing repeated extension — gymnasts, throwers, some cricketers and golfers — and they need different handling entirely.
And inflammatory back pain, which has a distinctive history: onset before forty, worse with rest, better with activity, prolonged morning stiffness, waking in the second half of the night. That pattern needs a rheumatologist, not a physical therapist, and recognising it is part of the job.
Red flags that stop the examination
Numbness in the saddle area, difficulty starting or controlling urination, loss of bowel control, or progressive weakness in both legs. Those are emergency symptoms and mean an emergency department the same day, not an appointment.
Unexplained weight loss, night pain that does not vary with position, a history of cancer, fever, or a significant fall in somebody with osteoporosis all move the conversation to a physician first.
None of these are common. Recognising them is nevertheless the reason the examination starts where it does rather than with the sore spot.
What you can tell before you get examined
Two simple observations are worth making at home. First, whether sitting for twenty minutes makes it worse — that is a useful piece of information either way.
Second, whether anything makes the leg symptoms retreat upward. If lying on your front on your elbows for a few minutes moves pain out of the calf and into the buttock, that is worth knowing and worth reporting.
Neither replaces an examination. Both make the first visit considerably more efficient.
Why people get told it is a muscle
Because it is the safe answer, and because most acute back pain does settle. If you tell everybody it is muscular and to rest, most of them improve and you appear to have been right.
The problem is the group who do not improve, who then spend months on the wrong plan because nobody re-examined the original assumption.
The useful rule: if a back has not meaningfully changed in three to four weeks of sensible management, the diagnosis deserves revisiting rather than the treatment deserving repeating.
The overlap that makes this hard
A disc problem produces muscle guarding around it, so a disc-driven back will have tight, tender muscles that are entirely real and entirely secondary.
Treat those muscles and the person feels better for a day, because you have reduced a symptom. The driver has not changed, so it returns, and the cycle repeats until somebody asks why the tightness keeps coming back.
That is why the sequence matters. Address the driver, and the guarding usually settles on its own; address only the guarding, and you are on a schedule.
It also explains why so many people describe months of massage that helped every time and never lasted. The treatment was working exactly as it should on the wrong target.
What an examination here involves
History first, and it does most of the diagnostic work. Then observation of how you actually move, active and passive range, repeated movement testing, neurological screening if there is any leg involvement, and specific tests for the hip and sacroiliac joint to exclude them.
Then a straight statement of what the findings suggest and what the plan is, including what would change it and roughly how long before you should expect to know.
If the findings point somewhere other than physical therapy, you get told that on the first visit rather than after six of them.
