Why sitting hurts the back of the thigh, and what no study has countedEmerging evidence
Sitting puts your weight on the sit bones, where the hamstring tendons attach, bends the hip and keeps you still, and the sciatic nerve runs about 1.2 cm from the side of the sit bone. No study counts the causes of hamstring pain when sitting. The commonest pattern in the sources is the high hamstring tendon, where sitting pain is a typical feature, but only one surgical series counts it (8 of 17 elite athletes, 47%); the rest of this guide's map comes from condition reviews, trials and case series, and says so.
How it started is the best clue: an ache that built up over weeks points to the tendon, a sudden pull in sport to a strain, a pop with bruising to a torn tendon, and burning or tingling past the knee to the nerve.
Sources 1, 2, 3, 4
The high hamstring tendonStrong evidence
High (proximal) hamstring tendinopathy is a deep, local ache at the sit bone, low in the buttock, worse with "prolonged and hard surface sitting, squatting, and walking uphill or running", coming on gradually without a single injury. It sometimes spreads down the back of the thigh (to the back of the knee in 4 of 17 athletes in one series). Sitting and bending the hip press the tendon against the bone, which is the leading explanation for why sitting hurts, from scans, surgery and expert reasoning rather than a direct test.
It affects runners, sprinters and field-sport players, and people who don't play sport: in the largest trial, people were about 45 on average and 74% were women, and a review links it with less active women around the menopause. Sitting pain "may persist for up to a year", an expert review says.
Sources 1, 4, 3, 2, 5, 6
A strain, a torn tendon, or a teenager's pulled-off growth plateStrong evidence
A strain is a sudden sharp pain at the back of the thigh during exercise, sometimes with a snap or pop, then tenderness, swelling and bruising after a few hours, as the NHS describes. The NHS page doesn't mention sitting; sitting may hurt for the first days (our reading).
A tendon torn off the sit bone (a proximal avulsion) is rare and often mistaken for a strain. It usually follows a slip, a high kick or waterskiing with the hip bent and the knee straight; in 263 people who had surgery, the average age was 49 and 52% were hurt in sport. The signs are a pop, large bruising, hard walking and sometimes tingling from pressure on the sciatic nerve. In one cohort, people repaired more than 6 weeks after the injury reported more weakness and more trouble sitting. In teenagers, the same pull can take a piece of growth plate with it, with pain "especially when sitting".
Sources 7, 8, 9, 10, 11, 12
The sciatic nerve and the backEmerging evidence
Sciatica brings pain from the bottom down the back of the leg, often into the foot, with burning, tingling, numbness or weakness, and it can be worse moving, sneezing or coughing, the NHS says. Near the sit bone, tight tendon tissue can irritate the sciatic nerve ("hamstring syndrome"), with pain on sitting, stretching and fast running; in surgical series, freeing the nerve relieved 52 of 59 people, and 77% of 44 athletes went back to sport. Repeated hamstring "strains" can come with a sensitive nerve.
Pain can also be referred from the back without nerve signs: a review describes a disc causing "a dull pain in the posterior thigh with sitting". Tendon pain is usually well localised and referred pain more spread out. Pain on getting up from sitting went with both disc and sacroiliac (SI) joint pain in 81 people having diagnostic injections, and leaning forward stretches the sciatic nerve, as in the slump test.
Sources 13, 14, 15, 16, 9, 17, 18, 19
One swollen, throbbing or hot leg is differentStrong evidence
A blood clot in a leg vein (a deep vein thrombosis) usually causes throbbing pain in the calf or thigh, swelling in one leg, and red, blue or darkened skin, which can be harder to see on brown or black skin. It is more likely after surgery, 3 or more days in bed or a journey of more than 4 hours, and the NHS advice for long journeys is to "get up and move around every hour or so". It needs an urgent GP appointment or NHS 111, and sudden breathlessness or chest pain with it is a 999 call.
A thigh that is hot, swollen or tender, especially without an injury you can remember, needs your GP practice or NHS 111 (NHS inform). After an injury, a leg that is twisted or bent, a bone sticking out, or signs of shock are a 999 call (the NHS).
Sources 20, 21, 22, 23
Lying down, getting up, the car and the toilet
Lying on your back with the legs straight takes the squeeze off the tendon, so tendon pain often eases lying down (our reading). Leg pain when you lie still is more often the nerve, and pain that wakes you night after night, with a fever or weight loss, needs a GP.
Getting up loads the tendon after a long squeeze, so the first steps can be sore (our reading). The toilet, the car and leaning forward all bend the hip further and press the sit bones; long drives on a hard seat aggravated it in one runner's case report, and leaning forward also stretches the sciatic nerve.
Sources 24, 18, 19, 13
What a scan shows, and what it doesn'tStrong evidence
The tendon is diagnosed by examination: tenderness at the sit bone, pain when the hamstring works against resistance, and stretch tests, which were reliable in 92 athletes, though their accuracy is probably overstated. Scans mislead here: 52% of 253 people with no symptoms had tendon changes on both sides on magnetic resonance imaging (MRI), over 90% of tendons showed signal changes in another study whether they hurt or not, and an NHS trust leaflet says scans "can show findings on those without pain".
A scan matters when a tendon may have torn off the bone: ultrasound or MRI promptly, because it is easily missed and the bruising can be slight; an X-ray shows a pulled-off piece of bone in a teenager. For sciatica, the National Institute for Health and Care Excellence (NICE) advises no routine scans outside specialist care, and NHS inform suggests one if symptoms haven't changed after 12 weeks and you'd consider surgery. A suspected clot needs a leg vein ultrasound, within 24 hours of referral, the NHS says.
Sources 2, 25, 26, 27, 28, 11, 12, 29, 30, 20
How it usually goesEmerging evidence
Tendon pain is often long-standing: people in the largest trial had had it for a median of about a year, and improved gradually to 52 weeks, most of it by 12 weeks. Strength can take "three to six months or more" to match the other side, and sitting pain can be the last thing to go. Mild strains usually get better in a few days and severe ones can take weeks or months; after a repaired avulsion, rehabilitation "typically takes at least 6 months". Sciatica usually gets better in a few weeks to a few months. No one can promise a date.
Sources 6, 1, 2, 7, 8, 13
