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Hip Flexors

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Introduction

The hip flexors are the muscles that bring the thigh toward the trunk, or the trunk toward the thigh, at the hip joint, with iliopsoas as the primary flexor.[1] Rectus femoris, sartorius, pectineus and tensor fasciae latae (TFL) assist, and their contribution changes with hip position and load.[2] These muscles work with every step: swinging the leg forward in gait and running, lifting the leg to climb stairs and generating the 'kicking motion', and helping bring the trunk forward when rising from a chair or sit-up. Because several of them also cross the knee, pelvis or lumbar spine, hip flexor problems often present as groin, anterior thigh or low back symptoms rather than as isolated hip pain.[3]

Anatomy

Six key muscles contribute to hip flexion:

  1. Psoas Major (Primary)
  2. Iliacus (Primary)
  3. Rectus Femoris (Secondary; Biarticular)
  4. Sartorius (Secondary)
  5. Pectineus (Secondary)
  6. Tensor Fasciae Latae (Secondary)
Hip muscles anterior aspect.
Hip muscles anterior aspect.
Muscle Proximal attachment Distal attachment Innervation Main actions at the hip
Psoas major T12–L5 vertebral bodies and discs;L1–L5 transverse processes[4] Lesser trochanter, via the iliopsoas tendon[5] Anterior rami L1–L3[6] Flexion; stabilises the lumbar spine[7]
Iliacus Iliac fossa[8] Lesser trochanter and femoral shaft just below it[9] Femoral nerve (L2–L4)[10] Flexion[11]
Rectus femoris Anterior inferior iliac spine; superior acetabular rim[12] Patella, then tibial tuberosity[13] Femoral nerve(L2–L4)[14] Hip flexion; knee extension[15]
Sartorius Anterior superioriliac spine[16] Proximal medialtibia (pesanserinus)[17] Femoral nerve(L2–L3)[18] Hip flexion,abduction,external rotation; knee flexion[19]
Pectineus Superior pubic ramus (pectineal line)[20] Pectineal line of femur[20] Femoral nerve; often obturator[20] Hip flexion,adduction[20]
Tensor fasciae latae Anterior superior iliac spine;anterior iliac crest[21] Gerdy'stubercle, via the iliotibial tract[21] Superior gluteal nerve(L4–L5)[21] Hip flexion,abduction,internal rotation[21]

Anatomically Significant Structures

Iliopsoas Tendon: Formed by the convergence of the psoas major and iliacus muscle bellies as they pass deep to the inguinal ligament. It courses anterior to the hip joint capsule and over the iliopectineal eminence before inserting into the lesser trochanter.[5][22][23]

Iliopectineal (Iliopsoas) Bursa: The largest bursa in the human body, situated directly between the iliopsoas tendon and the anterior hip joint capsule/pubic bone[24]. In approximately 15% of individuals, this bursa communicates directly with the hip joint cavity, providing a route for synovial fluid transfer or inflammation propagation.[24]

Capsular and Ligamentous Relationships: The deep surface of the iliopsoas tendon lies in direct proximity to the anterior hip joint capsule and the iliofemoral ligament (Y-ligament of Bigelow), contributing to anterior joint stability during extension.[7]

Anatomical Variations and Clinical Significance

Multi-Tendon Iliopsoas Architecture: While traditional anatomical models depict a single conjoint iliopsoas tendon, cadaveric studies demonstrate that over 50% of individuals possess two or three distinct tendon slips at the level of the lesser trochanter.[22][23]

Clinical Impact: Multi-tendon configurations are a primary mechanical factor in internal snapping hip syndrome (coxa saltans) as the individual slips roll over each other or the iliopectineal eminence. [22] Furthermore, incomplete surgical release during iliopsoas tenotomy often results from an unreleased secondary tendon slip, leading to persistent post-operative snapping. [22][23]

Function

Functional hip flexion relies on coordinated force generation across both monoarticular (single-joint) and biarticular (multi-joint) muscles.[1]

Monoarticular hip flexors (such as the iliacus and pectineus) cross only the acetabulofemoral joint, producing local torque dedicated purely to hip movement regardless of distal joint positions.[25] In contrast, biarticular hip flexors (such as the rectus femoris, sartorius, and tensor fasciae latae) cross both the hip and knee joint and rectus femoris is loaded most when hip flexion and knee extension combine as in kicking.[12][15][16][25] While psoas major uniquely spans the hip joint and the lumbar spine.[25] Consequently, the force production, mechanical advantage, and moment arms of biarticular flexors are highly dependent on the position and movement of adjacent joints; a phenomenon governed by length-tension relationships and active/passive insufficiency.[25]

Pelvic and Lumbar Spine Control

Pelvic Kinematics: Hip flexors inserting on the anterior ilium (iliacus, rectus femoris, TFL, sartorius) generate an anterior pelvic tilt moment.[26] [27] Antagonist co-contraction from the anterior abdominal wall (rectus abdominis and obliques) is required to stabilise the pelvis and prevent excessive anterior tilt during strong hip flexion.[7][26][27][15][20]

Lumbar Spine Mechanics (Psoas Major): Because psoas major attaches proximally to the T12–L5 vertebrae and intervertebral discs:

In open-chain activities (e.g., leg raises), psoas major exerts an anterior/superior shear force on the lumbar spine, increasing lumbar lordosis if abdominal stabilization is insufficient.[1]

In closed-chain activities (e.g., rising from a chair or perform sit-ups), psoas major pulls the trunk forward over the fixed femur, serving as an essential link between the upper body and lower extremity.[1]

Position Dependence

The adductors and TFL change their contribution to flexion with the starting hip angle, which is why testing position matters when assessing hip flexor strength or length.[28]

Physiotherapy Relevance

Assessment of the hip flexors should start from a clinical diagnosis, because the Doha consensus classifies groin pain in athletes (including iliopsoas-related groin pain) from history and physical examination rather than imaging.[29]

Assessment

  • Flexibility: The Thomas test and modified Thomas test are the standard clinical tests. A 2025 systematic review and meta-analysis found generally high intra- and inter-rater reliability, but protocols vary widely and need standardising.[30]
  • Validity caveat. The modified Thomas test is not a valid measure of hip extension unless pelvic tilt is controlled, therefore, a positive test is not proof of hip flexor shortening.[31]

Rehabilitation

  • For athletic groin pain, exercise therapy is supported as a core part of rehabilitation, particularly strengthening of the hip and abdominal muscles in functional, sport-like positions.[32]
  • Active strengthening of hip and abdominal muscles gave better short-term pain and return-to-sport outcomes than passive physiotherapy.[33]

Influence of Sitting Posture on the Hip Flexors

Prolonged sitting is associated with less passive hip extension.[34] Rather than sitting mechanically "breaking" the back or permanently shortening muscles on its own, pain is usually multi-factorial, involving reduced overall physical activity, muscle fatigue from slumped postures, decreased trunk motor variability, and individual tolerance to static loads.[34][35][36][37]

In a cross-sectional study[35] of 98 adults, people who were inactive and sat sevven or more hours a day had 6.1° less modified Thomas test hip extension than people who were active and sat 4 hours or less a day. The correlation between sitting time and hip extension was low and the authors could not exclude bony restriction or prove causality.

A systematic review of 26 studies[38] found no evidence that chairs reducing seated hip flexion lessen low back pain or consistently change trunk muscle activation.

On this evidence[35], it is reasonable to encourage physical activity and breaks from prolonged sitting in people with limited hip extension, as the study authors tentatively suggest.

Lower Crossed Syndrome

In lower crossed syndrome, there is overactivity and tightness of hip flexors and lumbar extensors. Along with this there is underactivity and weakness of the deep abdominal muscles on the ventral side and of the gluteus maximus and medius on the dorsal side.

Injuries and Related Conditions

Hip flexor injuries are best described by site and mechanism, using the Doha terminology for groin pain in athletes.[29]

Iliopsoas-related groin pain:

The Doha agreement named iliopsoas-related groin pain asone of four defined clinical entities of groin pain in athletes, alongside adductor-, inguinal-and pubic-related groin pain; hip-related groin pain and other causes are classified separately.[29]

Proximal rectus femoris injury:

80% of proximal rectus femoris injuries occurred while kicking and 20% while sprinting.[39]

Internal snapping hip:

The painful, audible movement of the iliopsoas tendon over theiliopectineal eminence or femoral head is called internal snapping hip syndrome.[22] Initial management is conservative: analgesia, physiotherapy and lifestyle modification.[22][23] Tenotomy is considered only for persistent, disabling pain, partly because of post-operative hip flexion weakness.[22] Because many people have more than one iliopsoas tendon, recurrence after release has been attributed to an unreleased tendon.[22][23]

Summary

The hip flexors are the muscles that bring the thigh toward the trunk at the hip, with iliopsoas as the principal flexor, assisted by rectus femoris, sartorius, pectineus and TFL. Clinically, the Thomas test is reliable but only valid if pelvic tilt is controlled. Prolonged sitting is associated with about 6° less hip extension, but that does not prove the hip flexors shorten or cause back pain. Athletic groin pain is best managed with active hip and abdominal strengthening. Injuries are classified using the Doha terminology (iliopsoas-related groin pain). Proximal rectus femoris injuries mostly occur while kicking, and internal snapping hip is treated conservatively first, with tenotomy reserved for persistent pain.

See Also

References

  1. ↑ 1.0 1.1 1.2 1.3 Juan J, Leff G, Kevorken K, Jeanfavre M. Hip flexor muscle activation during common rehabilitation and strength exercises. Journal of Clinical Medicine. 2024 Nov 4;13(21):6617.
  2. ↑ Lewis CL, Sahrmann SA, Moran DW. Effect of position and alteration in synergist muscle force contribution on hip forces when performing hip strengthening exercises. Clinical Biomechanics. 2009 Jan 1;24(1):35-42.
  3. ↑ Prather H, van Dillen L. Links between the hip and the lumbar spine (hip spine syndrome) as they relate to clinical decision making for patients with lumbopelvic pain. PM&R. 2019 Aug;11:S64-72.
  4. ↑ Kepler CK, Bogner EA, Herzog RJ, Huang RC. Anatomy of the psoas muscle and lumbar plexus with respect to the surgical approach for lateral transpsoas interbody fusion. European Spine Journal. 2011 Apr;20(4):550-6.
  5. ↑ 5.0 5.1 Manske RC, Voight M, Wolfe C, Page P, Bardowski B. The use of diagnostic musculoskeletal ultrasound for the evaluation of the Iliopsoas in the anterior hip: A guide for rehabilitation providers. International Journal of Sports Physical Therapy. 2024 Dec 2;19(12):1642.
  6. ↑ Siccardi MA, Tariq MA, Valle C. Anatomy, bony pelvis and lower limb: psoas major. InStatPearls [Internet] 2023 Aug 8. StatPearls Publishing.
  7. ↑ 7.0 7.1 7.2 Penning L. Psoas muscle and lumbar spine stability: a concept uniting existing controversies: critical review and hypothesis. European Spine Journal. 2000 Dec;9(6):577-85.
  8. ↑ Stella SM, Saponara A, Gualtierotti R, Vita F, Miccoli M, Becciolini M, Galletti S, Cotellessa F, Trompetto C. Thickening of the Intramuscular Fascia of the Iliacus Muscle as Evidence of Myofascial Pathology: A New Hip Pain Syndrome. Pain and Therapy. 2025 Dec;14(6):1935-47.
  9. ↑ Gómez-Hoyos J, Schröder R, Palmer IJ, Reddy M, Khoury A, Martin HD. Iliopsoas tendon insertion footprint with surgical implications in lesser trochanterplasty for treating ischiofemoral impingement: an anatomic study. Journal of Hip Preservation Surgery. 2015 Dec 1;2(4):385-91.
  10. ↑ Seijo-Martınez M, del Rı́o MC, Fontoira E, Fontoira M. Acute femoral neuropathy secondary to an iliacus muscle hematoma. Journal of the neurological sciences. 2003 May 15;209(1-2):119-22.
  11. ↑ Kumazaki T, Takahashi T, Nakano T, Sakai T. Action and contribution of the iliopsoas and rectus femoris as hip flexor agonists examined with anatomical analysis. Juntendo Medical Journal. 2022;68(4):352-62.
  12. ↑ 12.0 12.1 Carton P, Filan D. Anterior inferior iliac spine (AIIS) and subspine hip impingement. Muscles, Ligaments and Tendons Journal. 2016 Dec 21;6(3):324.
  13. ↑ Flores DV, Mejía Gómez C, Pathria MN. Layered approach to the anterior knee: normal anatomy and disorders associated with anterior knee pain. Radiographics. 2018 Nov;38(7):2069-101.
  14. ↑ Patton RS, Runner RP, Lazarus D, Bradbury TL. Femoral neuropathy following direct anterior total hip arthroplasty: an anatomic review and case series. Journal of Surgical Case Reports. 2018 Sep;2018(9):rjy171.
  15. ↑ 15.0 15.1 15.2 Aguilera‐Bohorquez B, Gil E, Fonseca J, Fernandez M, Sánchez M. Tenosuspension of the reflected head of the rectus femoris in hip arthroscopy: Description of a portal and a surgical maneuver. Arthroscopy techniques. 2017 Aug;6(4):e1015-9.
  16. ↑ 16.0 16.1 Yi KH, Lee JH, Lee DK, Hu HW, Seo KK, Kim HJ. Anatomical locations of the motor endplates of sartorius muscle for botulinum toxin injections in treatment of muscle spasticity. Surgical and Radiologic Anatomy. 2021 Dec;43(12):2025-30.
  17. ↑ Ashaolu JO, Osinuga TS, Ukwenya VO, Makinde EO, Adekanmbi AJ. Pes anserinus structural framework and constituting tendons are grossly aberrant in Nigerian population. Anatomy research international. 2015;2015(1):483186.
  18. ↑ Walters BB, Varacallo M. Anatomy, bony pelvis and lower limb, thigh sartorius muscle.
  19. ↑ Dziedzic D, Bogacka U, Ciszek B. Anatomy of sartorius muscle. Folia morphologica. 2014;73(3):359-62.
  20. ↑ 20.0 20.1 20.2 20.3 20.4 Dede BT, Oğuz M, Alyanak B, Bağcıer F. Orphan muscle of groin pain: ultrasound imaging of the pectineus muscle. Journal of Ultrasonography. 2024 Dec 31;24(99):1-2.
  21. ↑ 21.0 21.1 21.2 21.3 Gottschalk FR, Kourosh SO, Leveau B. The functional anatomy of tensor fasciae latae and gluteus medius and minimus. Journal of anatomy. 1989 Oct;166:179.
  22. ↑ 22.0 22.1 22.2 22.3 22.4 22.5 22.6 22.7 Lin B, Bartlett J, Lloyd TD, Challoumas D, Brassett C, Khanduja V. Multiple iliopsoas tendons: a cadaveric study and treatment implications for internal snapping hip syndrome. Archives of Orthopaedic and Trauma Surgery. 2022 Jun;142(6):1147-54.
  23. ↑ 23.0 23.1 23.2 23.3 23.4 Philippon MJ, Devitt BM, Campbell KJ, Michalski MP, Espinoza C, Wijdicks CA, LaPrade RF. Anatomic variance of the iliopsoas tendon. The American journal of sports medicine. 2014 Apr;42(4):807-11.
  24. ↑ 24.0 24.1 Corvino A, Venetucci P, Caruso M, Tarulli FR, Carpiniello M, Pane F, Sabatino V, Franzese R, Catalano O, Corvino F, Catelli A. Iliopsoas bursitis: the role of diagnostic imaging in detection, differential diagnosis and treatment. Radiology Case Reports. 2020 Nov 1;15(11):2149-52.
  25. ↑ 25.0 25.1 25.2 25.3 Neumann DA. Kinesiology of the hip: a focus on muscular actions. Journal of Orthopaedic & Sports Physical Therapy. 2010 Feb;40(2):82-94.
  26. ↑ 26.0 26.1 Daniels M. Anterior Pelvic Tilt.
  27. ↑ 27.0 27.1 Ludwig O, Dindorf C, Kelm S, Kelm J, Fröhlich M. Muscular strategies for correcting the pelvic position to improve posture—An exploratory study. Journal of functional morphology and kinesiology. 2024 Jan 29;9(1):25.
  28. ↑ Kato T, Taniguchi K, Kikukawa D, Kodesho T, Katayose M. Effect of hip flexion angle on stiffness of the adductor longus muscle during isometric hip flexion. Journal of Electromyography and Kinesiology. 2021 Feb 1;56:102493.
  29. ↑ 29.0 29.1 29.2 Weir A, Brukner P, Delahunt E, Ekstrand J, Griffin D, Khan KM, Lovell G, Meyers WC, Muschaweck U, Orchard J, Paajanen H. Doha agreement meeting on terminology and definitions in groin pain in athletes. British journal of sports medicine. 2015 Jun;49(12):768-74.
  30. ↑ González‐de‐la‐Flor Á, Seijas‐Otero D. Reliability of physical examination tests for assessing hip flexor flexibility: A systematic review and meta‐analysis. PM&R. 2026 Jul;18(7):779-92.
  31. ↑ Vigotsky AD, Lehman GJ, Beardsley C, Contreras B, Chung B, Feser EH. The modified Thomas test is not a valid measure of hip extension unless pelvic tilt is controlled. PeerJ. 2016 Aug 11;4:e2325.
  32. ↑ Machotka Z, Kumar S, Perraton LG. A systematic review of the literature on the effectiveness of exercise therapy for groin pain in athletes. BMC Sports Science, Medicine and Rehabilitation. 2009 Mar 31;1(1):5.
  33. ↑ Almeida MO, Silva BN, Andriolo RB, Atallah ÁN, Peccin MS. Conservative interventions for treating exercise‐related musculotendinous, ligamentous and osseous groin pain. Cochrane database of systematic reviews. 2013(6).
  34. ↑ 34.0 34.1 Ehresman BA, Lehecka BJ, Hiser D, Koster L, Wietharn J. Improved hip flexibility and gluteal function following a daily lunge-and-reach stretching intervention. International Journal of Sports Physical Therapy. 2025 Jun 2;20(6):814.
  35. ↑ 35.0 35.1 35.2 Boukabache A, Preece SJ, Brookes N. Prolonged sitting and physical inactivity are associated with limited hip extension: A cross-sectional study. Musculoskeletal Science and Practice. 2021 Feb 1;51:102282.
  36. ↑ Jung KS, Jung JH, In TS, Cho HY. Effects of prolonged sitting with slumped posture on trunk muscular fatigue in adolescents with and without chronic lower back pain. Medicina. 2020 Dec 23;57(1):3.
  37. ↑ Chan YL, Leung SL, Chau WW, Wong RM, Au BK. Slumped sitting posture is associated with chronic low back pain amongst older adults in long-term care facilities: a cross-sectional study. Geriatric Nursing. 2026 Sep 1;72:104185.
  38. ↑ Curran M, O’Sullivan L, O’Sullivan P, Dankaerts W, O’Sullivan K. Does using a chair backrest or reducing seated hip flexion influence trunk muscle activity and discomfort? A systematic review. Human Factors. 2015 Nov;57(7):1115-48.
  39. ↑ Bogwasi L, Holtzhausen L, van Rensburg DJ, van Rensburg AJ, Botha T. Management of proximal rectus femoris injuries–do we know what we’re doing?: A systematic review. Biology of Sport. 2023 Apr 1;40(2):497-512.
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