Hip flexors

The hip flexors are the muscles at the front of the hip that lift your thigh towards your body. The largest and most important is the iliopsoas, which runs from the lower spine and the inside of the pelvis to the top of the thigh bone and is the main flexor of the thigh (Bordoni & Varacallo, 2026).

Which muscles are the hip flexors?

Four muscles at the front of the hip and thigh flex the hip (TeachMeAnatomy):

• Iliopsoas, made of two muscles. The psoas major starts on the lumbar vertebrae, and the iliacus lines the inside of the pelvis. Both attach to the lesser trochanter, a bump on the inner side of the upper thigh bone (Bordoni & Varacallo, 2026).
• Rectus femoris, one of the four quadriceps muscles and the only one that crosses both the hip and the knee. It flexes the hip and straightens the knee.
• Sartorius, a long strap of muscle from the front of the pelvis to the inside of the knee, which also flexes the knee.
• Pectineus, a short muscle in the groin that also draws the thigh inwards.

The psoas has a direct link with the back. Its deeper part starts from the first four lumbar vertebrae, and its more superficial part from the sides of the lowest vertebrae of the thoracic spine and the discs next to them (Siccardi et al., 2023).

What do the hip flexors do?

Their main job is bending the hip, which lifts the thigh forward. The iliopsoas also helps rotate the hip outwards and helps stabilise the hip and the lumbar spine (Bordoni & Varacallo, 2026).

Does sitting make your hip flexors tight?

The reasoning sounds convincing. When you sit, your hips are bent, so the hip flexors spend hours in a shortened position, and over months they are said to adapt and pull on the lower back. Your chair height changes how sharply the hips bend while you sit. Researchers describe tight hip flexors as “frequently assumed” to contribute to low back pain, while noting that the nature of the relationship is unclear (Eimiller et al., 2026).

The direct evidence is thin:

• In 46 desk workers who had worked at a desk for at least five hours a day for five years, shorter iliopsoas measurements went with a deeper curve in the lower back (Singhvi & Bharnuke, 2024). The study was small, only looked at one point in time, and could not show which came first.
• In 118 adults who hadn’t sought care, those with low back pain had slightly less hip extension on the standard test for hip flexor length. Once other factors were taken into account, back pain was no longer independently linked with hip flexor length; body mass index was the only significant factor (Eimiller et al., 2026).

So the fair summary is that hip flexor length may matter for some people, but it hasn’t been shown to be a major cause of back pain from sitting. It is one of the ideas grouped under muscle imbalance, a concept with mixed evidence. The time itself is worth knowing about for other reasons, which is what the entry on sedentary behaviour covers, and the sitting time calculator shows how many hours you spend in a chair.

Which conditions involve the hip flexors?

• Lower back pain from sitting, where the hip flexors are usually discussed alongside the erector spinae, the long back muscles.
• Hip and groin problems. The iliopsoas can be involved in tendinopathy, bursitis and snapping hip. Because it lies close to the organs of the abdomen and pelvis, its problems can mimic other conditions there or nerve problems (Bordoni & Varacallo, 2026).

When should you see a doctor?

See a GP if hip pain is stopping you doing normal activities or affecting your sleep, or if it hasn’t improved after two weeks of treating it at home. Ask for an urgent GP appointment or contact NHS 111 if your hip is swollen and feels hot, or you have hip pain with a high temperature or feel generally unwell. Call 999 or go to A&E if you have severe hip pain after a fall or injury, can’t put weight on your leg, or have tingling or loss of feeling in the hip or leg after an injury (NHS). If back pain comes with numbness or weakness in both legs, or changes in bladder or bowel control, call 999 (NHS).

Stretches for the front of the hip are part of Bavelu’s lower back sessions, designed and filmed by physiotherapists.