When the spasm is coming from an irritated nerve

Sciatica is not a diagnosis in itself. It's a description: pain travelling along the path of the sciatic nerve, from the low back or buttock down the back of the thigh, sometimes past the knee into the calf or foot. Something is irritating that nerve, and the interesting question is what.

Why nerve irritation causes a spasm

A nerve root under mechanical pressure or chemical irritation is an unusually loud threat signal. The spinal cord's response is the same one it uses for anything it reads as potential damage: clamp the segment down so nothing moves and nothing gets worse.

That's why so many people with sciatica describe the back as the thing that seizes, while the leg is the thing that burns. The spasm is the protection. The nerve is the reason for it.

There's a second layer. A nerve that's irritated is also mechanically sensitive — it doesn't glide through the surrounding tissue as freely as it should. Movements that would normally lengthen and slide the nerve, like bending forward or straightening the leg, now tug on something already angry, and the guarding response fires again.

What it usually feels like

• Pain that travels, rather than sitting in one spot
• Burning, electrical or shooting quality, distinct from the deep ache of muscle
• Often worse sitting, worse getting out of a car, worse first thing in the morning
• May come with pins and needles, numbness, or a leg that feels weak or heavy
• Coughing or sneezing can send a jolt down the leg

Pure muscular spasm tends to stay local, feels like a vice or a cramp, and doesn't produce those electrical or numb qualities below the knee.

During the acute phase

The three immediate steps apply here as they do to any spasm. Two things are worth adding:

Find the position that quiets the leg, not just the back. Many people with nerve irritation are most comfortable lying on the unaffected side with the painful leg supported on pillows, or on their back with the knees high. Others cannot tolerate sitting at all for a few days. Let the leg symptoms be your guide — if a position increases the travel of the pain down the leg, it's the wrong position, even if the back feels better in it.

Watch the direction of travel. Symptoms retreating up the leg towards the back over days is a good sign, even if the back pain itself gets temporarily louder. Symptoms spreading further down is a sign to stop whatever you're doing and get assessed.

What tends to make it worse

• Prolonged sitting, especially in a soft low seat
• Bending forward to pick things up, including with a "good" technique, in the first few days
• Aggressive hamstring stretching, which pulls directly on an inflamed nerve
• Being told to push into the pain to "free it up"

Get assessed if

Go to emergency care immediately for loss of bladder or bowel control, numbness through the groin or saddle area, or weakness affecting both legs. Those are not sciatica.

Otherwise, book an appointment if the pain goes below the knee and doesn't start improving within a week or two, if you have a foot that drags or catches, if there's measurable weakness, or if numbness is spreading rather than shrinking.

Nerve pain is one area where imaging and a proper neurological examination genuinely change the plan, rather than just confirming what you already know.

If you're in an acute spasm as you read this, start with the three immediate steps. This page is for working out what set it off.