Pain in the back of the thigh is one of the most common things people bring to a first visit. Sometimes it is a tight or strained hamstring. Sometimes it is sciatica, an irritated nerve that starts in the lower back. They feel alike, but they are treated differently, so it is worth telling them apart.

Check one: the slump test

Sit on the edge of a chair and let your back round forward. Tuck your chin, then slowly straighten one knee. Now lift your head and look up. If the pull in your leg eases when you look up, the nerve is likely involved. A hamstring does not care where your head is.

Check two: where and when it hurts

Hamstring pain usually sits in one spot in the muscle and hurts most when you stretch or sprint. Sciatica tends to travel below the knee or into the foot, and often comes with tingling, numbness, or pain that is worse after sitting.

• Hamstring: a local ache, worse with stretching, better with gentle movement.

• Sciatica: pain that travels, tingling or numbness, worse after sitting or bending.

Why it matters

Stretching a strained hamstring helps it heal. Stretching an irritated nerve hard usually makes it angrier. If the slump test points to the nerve, gentle nerve glides and finding the positions that ease your leg will do more than a long hamstring stretch.

See someone this week if

The numbness is spreading, your foot feels weak, or the pain wakes you every night. If you notice numbness in both legs or any change in bladder or bowel control, call 911 or go to the nearest emergency room.