Your hip flexors are a group of muscles at the front of your hip that pull your knee upward toward your chest. Every time you walk, climb stairs, sit down, or kick a ball, these muscles are doing the work. The group includes five muscles, but two of them handle most of the heavy lifting: the psoas major (which runs from your lower spine to your thighbone) and the iliacus (which lines the inside of your pelvis and attaches to the same spot on the thighbone). Together, these two are often called the iliopsoas, and they’re the primary drivers of hip flexion.
The Muscles That Make Up the Group
The hip flexors aren’t a single muscle. They’re a team of muscles that all contribute to the same motion: bringing your thigh closer to your torso. The iliopsoas is the strongest of the group. The psoas major originates from the sides of your lower spine, spanning from the lowest thoracic vertebra down to the fourth lumbar vertebra. The iliacus starts from the broad inner surface of your pelvis. Both muscles converge into a shared tendon that attaches to a small bony bump on the inside of your upper thighbone called the lesser trochanter.
Beyond the iliopsoas, three other muscles assist with hip flexion. The rectus femoris is the only part of your quadriceps that crosses the hip joint, making it a powerful flexor especially during the first 45 degrees of lifting your leg. The sartorius, the longest muscle in the body, runs diagonally across the front of your thigh and helps with flexion, rotation, and crossing your legs. The adductor longus, on your inner thigh, also chips in during certain movements. There’s also a small muscle called the psoas minor that sits in front of the psoas major, but it contributes very little to actual hip flexion and isn’t even present in everyone.
What Your Hip Flexors Actually Do
The simplest way to think about hip flexors: they close the angle between your torso and your thigh. That motion happens constantly throughout the day. Walking requires your hip flexors to swing your leg forward with each step. Running and sprinting demand even more from them, generating the explosive forward drive of each stride. Sitting down engages them to control the descent, and standing up from a chair requires them to help initiate the movement.
These muscles also play a critical role in stabilizing your pelvis and lower spine. The psoas major connects directly to your lumbar vertebrae, so it doesn’t just move your leg; it helps hold your spine in position during movement. When you lift your leg while lying on your back, the rectus femoris dominates the first half of the motion (0 to 45 degrees), while your abdominal muscles take over beyond 45 degrees to keep your pelvis from tilting forward.
How They Affect Your Posture and Back
Because the psoas major attaches directly to the lumbar spine, tight or shortened hip flexors can pull the front of your pelvis downward, creating what’s known as an anterior pelvic tilt. This tips your pelvis forward and exaggerates the curve in your lower back. Over time, this posture increases stress on the lumbar spine and can contribute to lower back pain, hip muscle strains, and even compression of the sciatic nerve as the pelvis rotates out of its neutral position.
The tilt typically happens when weak abdominal muscles can’t counterbalance the pull of the hip flexors. People who sit for long hours are especially prone to this, since the hip flexors stay in a shortened position all day. The good news: training the hip muscles alongside abdominal strengthening exercises (like drawing your belly button toward your spine to find a neutral pelvic position) has been shown to improve muscle strength, activation patterns, and pain in the lower back area.
Hip Flexor Strains
A hip flexor strain is a stretch or tear in one or more of these muscles, most commonly the iliopsoas or rectus femoris. It typically happens during explosive movements like sprinting, kicking, or sudden direction changes. Among NCAA athletes, hip flexor strains occurred at a rate of 1.60 per 10,000 athletic exposures, with the highest rates in men’s soccer and men’s ice hockey (ranging from 2.47 to 3.77 per 10,000 exposures).
Strains are graded by severity:
- Grade 1 (mild): Minor stretching or microscopic tears. You feel tightness and mild pain but can usually still walk and move.
- Grade 2 (moderate): A partial tear. Walking may cause a limp, and you’ll notice more significant pain, weakness, and possibly some swelling.
- Grade 3 (severe): A complete tear of the muscle or tendon. This causes significant pain, bruising, swelling, and an inability to use the muscle normally.
Common symptoms across all grades include a pulling sensation in the front of the hip, pain that worsens when lifting the knee, weakness in the hip or lower abdomen, muscle spasms, and in more severe cases, visible bruising or discoloration. A healthcare provider diagnoses the strain through a physical exam and may use ultrasound to check for tears or fluid buildup, or an MRI to rule out blood clots or internal bleeding in more severe injuries.
How Tightness Is Tested
The most common clinical test for hip flexor tightness is called the Thomas test. You lie on your back at the edge of an exam table, pull one knee to your chest, and let the other leg hang off the edge. If the thigh of your hanging leg rises off the table instead of resting flat, that signals tightness in the iliopsoas. If the knee of that same leg straightens out beyond 90 degrees, it points to tightness in the rectus femoris specifically. And if the leg drifts outward or rotates, the tensor fasciae latae or the band of tissue running along the outside of your thigh may be involved.
You can do a rough version of this test at home to get a general sense of your hip flexor flexibility, though a trained clinician will catch subtleties you might miss. The test is particularly useful because it isolates each muscle’s contribution, helping pinpoint exactly where the restriction is coming from.
Keeping Your Hip Flexors Healthy
If you sit for most of the day, your hip flexors spend hours in a shortened position. Over time, this can reduce their flexibility and set the stage for the postural problems described above. Regular stretching helps counteract this. A simple kneeling lunge stretch, where you place one knee on the ground and shift your hips forward while keeping your torso upright, targets the iliopsoas directly.
Strengthening matters just as much as stretching. Weak hip flexors force surrounding muscles to compensate, which can lead to strains during sudden or intense activity. Exercises like leg raises, marching in place with high knees, and resisted knee drives all build hip flexor strength progressively. Pairing these with core exercises is particularly effective, since your abdominals and hip flexors work as a team to stabilize your pelvis during nearly every movement you make.
For athletes or anyone returning to activity after a strain, gradual progression is key. Jumping back into sprinting or kicking before the muscle has fully healed is one of the most common ways people re-injure their hip flexors. Mild strains generally resolve in a few weeks with rest and gentle movement, while moderate to severe tears can take significantly longer and may require guided rehabilitation.