Hamstrings

The hamstrings are the three muscles at the back of the thigh: the biceps femoris, the semitendinosus and the semimembranosus. Together they straighten (extend) the hip and bend the knee, and they are supplied by the sciatic nerve (TeachMeAnatomy).

Where are the hamstrings?

All three start from the ischial tuberosity, the sit bone at the bottom of the pelvis. The one exception is the short head of the biceps femoris, which starts on the back of the thigh bone (TeachMeAnatomy). From there:

• the biceps femoris runs down the outer side of the thigh to the head of the fibula;
• the semitendinosus, a largely tendinous muscle, and the semimembranosus, a flat, broad one beneath it, run down the inner side to the tibia.

Except for that short head, the hamstrings cross two joints, the hip and the knee (Poudel & Pandey, 2023).

What do the hamstrings do?

At the knee they bend the leg; at the hip they pull the thigh back. They also turn the leg: the biceps femoris rotates outwards, the other two inwards (TeachMeAnatomy). They work in everything from standing upright to sprinting and jumping (Hu & Raja, 2026). With the gluteus maximus, they share the job of straightening the hip.

Does sitting shorten your hamstrings?

Because the hamstrings cross both the hip and the knee, sitting does two opposite things to them. Bending the knee slackens them at the bottom; bending the hip pulls on them at the top. That is one reason the common claim that chairs “shorten” the hamstrings is harder to pin down than it sounds, and we found no good evidence that desk work does.

The feeling of tightness is a separate question. A review of stretching research concluded that the extra range people gain after a single stretching session, and after programmes of three to eight weeks, seems to come mainly from changes in sensation, that is, tolerating more stretch, rather than from a longer muscle. The effects of longer programmes hadn’t been tested (Weppler & Magnusson, 2010). So “tight hamstrings” often describe how a stretch feels as much as how long the muscle is.

Do tight hamstrings cause back pain?

A review of 12 studies with 5,459 people looked at physical measurements taken at the start and then followed people for a year to see who developed low back pain. Restricted hamstring range of motion was linked with a higher chance of developing it, as were limited side bending of the trunk and a flatter lower back. The hamstring link was small, with an odds ratio of 0.96, and many other measures, including forward bending range of the lower back and back muscle strength, were not linked at all (Sadler et al., 2017). A link of that size can’t show that tight hamstrings cause back pain. Whether stretching or strengthening matters more is covered in Stretching or strengthening? and the bigger picture in lower back pain from sitting.

Hamstring pain at the sit bone

Deep pain in the buttock where the hamstrings attach can come from proximal hamstring tendinopathy. It affects people who play sport and people who don’t, is often long-standing and can limit daily activities. There is limited evidence on how best to diagnose and manage it, and no randomised trials of rehabilitation had been published when a 2016 clinical review was written (Goom et al., 2016).

When to see a doctor

Pain that runs from the buttock down the back of the leg, often into the foot, with tingling, numbness or weakness, is more likely to be sciatica than a tight muscle. See a GP if it hasn’t improved after a few weeks of home treatment, is getting worse or is stopping your normal activities. Go to A&E or call 999 if you have sciatica on both sides, severe or worsening numbness or weakness in both legs, numbness around your genitals or bottom, or changes in bladder or bowel control (NHS).