Your hip flexors are a group of muscles at the front of your hip that pull your knee upward toward your chest. They activate every time you walk, climb stairs, sit down, or kick a ball. Most people don’t think about them until something goes wrong, but these muscles play a central role in how you move and how you stand.
The Muscles That Make Up Your Hip Flexors
The term “hip flexor” doesn’t refer to a single muscle. It’s a group of muscles that all share one job: bending (flexing) the hip joint. The most important is the iliopsoas, which is actually two muscles that merge into one tendon. The psoas major runs from your lower spine, attaching along the sides of your lowest five vertebrae. The iliacus is a broad, fan-shaped muscle that lines the inside of your pelvis. These two muscles come together and attach to a small bump on the inside of your upper thighbone. The iliopsoas is the strongest hip flexor and also helps stabilize your spine and pelvis when you’re standing upright.
Several other muscles assist with hip flexion. The rectus femoris, one of the four quadriceps muscles on the front of your thigh, has a dual role: it flexes the hip and straightens the knee. The sartorius, a long strap-like muscle that crosses diagonally from your outer hip to your inner knee, flexes the hip while also helping rotate the leg outward. The pectineus, a smaller muscle in the inner groin area, contributes to hip flexion and pulls the thigh inward. Together, these muscles coordinate to produce smooth, powerful movement every time you lift your leg.
What Your Hip Flexors Do All Day
Hip flexion sounds simple, but it’s involved in more activities than most people realize. Walking requires your hip flexors to swing each leg forward with every step. Running and sprinting demand explosive hip flexion to drive the knees high and fast. Standing up from a chair, climbing into a car, and going up stairs all rely on this muscle group. Even lying in bed and pulling your knees up uses your hip flexors.
Beyond movement, the iliopsoas contributes to postural stability. It helps hold your torso upright when you’re standing and plays a role in lifting your upper body from a lying position. When these muscles are functioning well, you barely notice them. When they’re tight, weak, or injured, the effects ripple through your lower back, pelvis, and legs.
Why Sitting Makes Them Tight
When you sit, your hips stay bent at roughly 90 degrees. This keeps your hip flexor muscles in a shortened, slack position for hours at a time. Research shows that sitting more than seven hours a day, combined with low physical activity, is associated with increased passive stiffness in the hip flexors and reduced hip extension (the ability to straighten your leg behind you). Essentially, muscles that spend most of the day in a shortened position can adapt to that length and resist stretching back out.
The good news is that regular movement involving a stretch-shorten cycle, even something as basic as walking, can offset the effects of prolonged sitting. The problem arises when long sitting hours aren’t balanced with enough physical activity. Over time, chronically shortened hip flexors can pull the front of your pelvis downward, creating what’s called an anterior pelvic tilt. This tips the pelvis forward, exaggerates the arch in your lower back, and pushes your butt outward. That posture shift is a common contributor to lower back pain. It happens because the hip flexors, glutes, hamstrings, and abdominal muscles all work together to hold the pelvis level. When one group gets too tight or too weak, the balance breaks down.
Hip Flexor Strains and How They Feel
A hip flexor strain is a stretch or tear in one or more of these muscles. It typically causes pain at the front of the hip, where the thigh meets the torso, or in the groin area. The pain often gets worse when you lift your knee, walk, or try to sprint. In more significant strains, even standing comfortably can be difficult.
Strains are graded on a three-point scale:
- Grade 1: A mild pull with tiny tears in the muscle fibers. You feel discomfort but don’t lose strength, and the muscle stays its normal length.
- Grade 2: A moderate strain with more significant tearing in the muscle or tendon fibers. The tendon may be stretched longer than normal, and you’ll typically notice a loss of strength.
- Grade 3: A complete tear of the tendon. This is rare but serious.
These injuries are most common in athletes who sprint, kick, or change direction quickly, such as soccer players, runners, and martial artists. But they can also happen from something as mundane as a sudden slip or an awkward step off a curb.
How to Test for Tightness
A simple way to gauge hip flexor tightness is a version of the Thomas Test. You lie on your back at the edge of a bed or table with both legs pulled toward your chest. Then you lower one leg and let it hang off the edge while keeping the other knee hugged in. If the hanging thigh can’t drop to the level of the table surface (it stays elevated or you feel a strong pull at the front of the hip), that suggests your hip flexors on that side are shorter or stiffer than normal. It’s a quick screen, not a diagnosis, but it gives you useful information about where you stand.
Stretches That Help
Physical therapists at the Hospital for Special Surgery recommend holding hip flexor stretches for 30 seconds per side, repeating for three sets, at least twice a day. Two stretches are particularly effective.
The half-kneeling hip flexor stretch is the classic option. Kneel on one knee with the other foot flat on the floor in front of you, thigh parallel to the ground and knee bent at 90 degrees. Keep your back shin pointing straight behind you. Sink both hips toward the floor. For a deeper stretch, lean your chest slightly forward without collapsing your upper body or letting your hips rise. You should feel the stretch at the front of the hip on the kneeling side.
The supine hip flexor stretch works well if kneeling is uncomfortable. Lie on your back at the edge of a bed with both legs extended. Bend one knee and place that foot flat on the bed, keeping your lower back pressed down. Let the other leg hang off the side of the bed. Gravity gently pulls the hanging leg into extension, stretching the hip flexors without requiring you to balance.
Beyond stretching, strengthening the muscles that oppose tight hip flexors makes a significant difference. Glute bridges, planks, crunches, and clamshells help keep your glutes, core, and deep hip rotators strong, which improves overall hip mobility and takes pressure off the hip flexors. If you sit for long periods, changing position every 30 to 45 minutes helps prevent the muscles from stiffening up in a shortened state.