Understanding the Role of Hip Flexors in Running

Hip flexors are one of those things runners love to blame.

Tight hips. Short strides. Low back pain. That nagging feeling that something just isn’t working right. And while hip flexors are rarely the only issue, they play a meaningful role in how we run and how problems can start to show up.

The hip flexors are a group of muscles that help advance the leg during running. After your foot leaves the ground, they help bring the thigh forward so you can take your next step. They also assist with pelvic and trunk control, helping manage the forces that travel through the body with each stride.

The primary hip flexor, the iliopsoas, is made up of the psoas major and iliacus. The iliacus attaches to the pelvis, while the psoas originates from the lumbar spine. Together, they cross the hip joint and connect the trunk to the leg. Because of these attachments, hip flexors influence pelvic position, lumbar spine loading, and hip extension during running. When they are overloaded or underprepared, runners may notice changes in stride length, posture, or increased strain through the low back.

Hip flexors are not passive players in running. Musculoskeletal modeling research shows that the iliopsoas is a meaningful contributor to hip joint contact forces during the stance phase of running, alongside the gluteal muscles (Zhao et al.). This means hip flexors are actively involved in managing load at the hip, not just swinging the leg forward.

Running places repeated demands on the same tissues over and over again. Hip flexors are loaded thousands of times in a single run, often under fatigue. When training volume or intensity increases faster than a runner’s ability to tolerate that load, symptoms can appear.

Many runners describe hip flexors as “tight,” but tightness is a sensation, not a diagnosis. That feeling can reflect fatigue, reduced load tolerance, or altered coordination rather than true muscle shortening. When hip flexors struggle to tolerate training demands, runners may lose hip extension, shorten stride length, or shift movement toward the lumbar spine or pelvis.

Stretching is often the first response. Stretching can increase passive range of motion, but that change does not necessarily carry over into how someone runs. In runners with limited hip extension, a short-term hip flexor stretching program improved passive flexibility but did not change active hip extension, pelvic tilt, or lumbar spine motion during running at typical training speeds (Mettler et al.). Feeling looser does not automatically mean running differently.

Hip flexors can also contribute to symptoms when they lack strength or robustness. Running builds endurance, but hip flexors can still be underprepared for the demands of training especially when volume or intensity ramps faster than capacity. Repeated loading beyond tissue capacity increases the likelihood of persistent symptoms, particularly when early warning signs are ignored (Grassi et al.).

Hip flexors respond well to progressive strengthening, controlled loading, and thoughtful management of running volume and intensity. When capacity improves, symptoms often become less frequent and less limiting.

Take-Home Messages for Runners

• Hip flexors connect the trunk to the leg, which is why they influence stride length, posture, and low back stress.

• Feeling “tight” doesn’t always mean you need more stretching; it often means the tissue is fatigued or underprepared.

• Stretching can change flexibility, but it doesn’t automatically change running mechanics.

• Hip flexors help manage joint load during running and need strength and load tolerance, not just mobility.

• Addressing training load and building capacity matters more than chasing perfect hip flexibility.

You don’t need perfectly loose hips.You need hip flexors that can tolerate the work you ask them to do.

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Besomi, Mariana, et al. “Exploring Contextual Factors for Management and Prevention of Running-Related Injuries: Runners’ and Experts’ Perspectives.” BMJ Open Sport & Exercise Medicine, vol. 11, 2025, e002413. https://doi.org/10.1136/bmjsem-2024-002413.

Grassi, Alberto, et al. “An Update on the Grading of Muscle Injuries: A Narrative Review from Clinical to Comprehensive Systems.” Joints, vol. 4, no. 1, 2016, pp. 39–46.

Mettler, Jeffrey H., Robert Shapiro, and Michael B. Pohl. “Effects of a Hip Flexor Stretching Program on Running Kinematics in Individuals with Limited Passive Hip Extension.” Journal of Strength and Conditioning Research, vol. 33, no. 12, 2019, pp. 3338–3344.

Zhao, Kaiwei, Chun Shan, and Yan Luximon. “Contributions of Individual Muscle Forces to Hip, Knee, and Ankle Contact Forces During the Stance Phase of Running: A Model-Based Study.” Health Information Science and Systems, vol. 10, 2022, Article 11.