Overview of Female Pelvic Floor Muscle Anatomy and Physiology

Original Editor - Jess Bell based on the course by Z Altug
Top Contributors - Jess Bell, Kim Jackson and Rucha Gadgil

Introduction[edit | edit source]

The pelvic floor does not exist in isolation. It is part of a complex system that works synergistically with structures and systems both nearby and further away in the body, including the ankle / foot complex, the thorax and respiratory complex, the central nervous system and the brain.[1] Because the body is a dynamic, interrelated, fascially connected, biotensegral[2] system, it is important that pelvic health physiotherapists consider the contribution of all these systems and structures when assessing and treating pelvic health complaints.[1]

Figure 1. Bones of the pelvis.

The Pelvic Floor[edit | edit source]

Figure 2. Ligaments of the pelvis.
Figure 3. Muscles of the pelvic floor.

Health professionals might have differing views about what makes up the pelvic floor:[1]

  • Is it just comprised of the pelvic floor muscles?
  • Should the pelvic organs be included?
  • Is the hip joint part of the pelvic floor?
  • Are the contents of the lower abdominal cavity also included?

For the pelvic health physiotherapist, the pelvic floor refers to the area at the bottom of the pelvis, and all of its contents and associated structures, including:[1]

  • The pelvis itself (Figure 1)
    • Called the pelvic ring or pelvic bowl
    • Includes the pelvic joints
  • Pelvic organs
    • Bladder, uterus and rectum in women
  • Pelvic ligaments (Figure 2)
  • The endopelvic fascia and connective tissue
  • The nerves which innervate the pelvic region, as well as blood vessels and the lymphatic system
  • The external genitalia
  • The pelvic floor musculature (Figure 3 and 4)

Pelvic health physiotherapists are able to treat all these structures either directly or indirectly.

This page focuses on the anatomy of the female pelvic floor musculature. More information on the other structures within the pelvis is available here.

Pelvic Cavity[edit | edit source]

The abdominal and pelvic cavities are bordered at the front, top, back and bottom:[1][3]

  • The front border is the abdominal wall
  • The top border is the respiratory diaphragm
  • The back border is the spinal column
  • The bottom border consists of the pelvic floor muscles

Pelvic Floor Muscles[edit | edit source]

The pelvic floor muscles act to close off the bony outlet, which they do so completely apart from specific openings:[1][3]

  • The urogenital hiatus
    • Contains the urethra and vagina in women
    • Positioned anteriorly
  • The anal hiatus
    • Contains the anal canal
    • Positioned posteriorly

The muscles of the pelvic floor are divided into three layers.[6]

Figure 4. Muscles of the pelvic diaphragm.

Deep Layer - Pelvic Diaphragm[edit | edit source]

The deepest layer of the pelvic floor muscles is known as the pelvic diaphragm (see Figure 4). It is a broad, funnel-shaped sling of fascia and muscle suspended from bony anchor points in the lesser pelvis[1][7] (i.e. the area of the pelvic cavity below the linea terminalis[8]).

The muscles of the pelvic diaphragm are:[1][9] [10]

  • Ischococcygeus muscle (also known as the coccygeus muscle)
    • Originates from the ischial spine and inserts into the lateral aspect of the coccygeal vertebrae
  • Levator ani
    • A composite muscle that is traditionally divided into three parts:[1][11]
      • Pubococcygeus: originates from the internal surface of the pubic ramus and inserts into the lower sacral and coccygeal vertebrae
      • Illiococcygeus: originates at the arcus tendinous levator ani (ATLA) and fuses with the pubococcygeus
      • Puborectalis: originates at the inner surface of the right and left sides of the pubic bone. The two muscles meet behind the rectum and form a continuous sling

In this deep part of the pelvic floor, it is also possible to palpate the obturator internus and piriformis muscles. These muscles are not, however, considered to be part of the pelvic diaphragm. Instead, they are rotators of the hip.[1]  

Middle Layer - Urogenital Diaphragm / Perineal Membrane[edit | edit source]

The middle layer has traditionally been called the urogenital diaphragm, but is often now referred to as the perineal membrane.[1]

There is controversy over whether this layer contains:[10]

  • A transverse sheet of muscle called the deep transverse perinei muscle which is between an inferior and superior fascia OR
  • Three joined muscles and an inferior fascial layer (i.e. the perineal membrane)

However, the middle layer stretches across the urogenital triangle (see below) and in women, houses the urethral and vaginal sphincters (i.e. the sphincter urethrovaginalis, the external urethral sphincter, and the compressor urethrae). These sphincters close the urethra and vagina, and maintain continence.[1][12] The entire perineal layer provides additional support for the deeper pelvic floor structures.[1][10]

Figure 5. Muscles of the superficial layer.

Superficial Layer[edit | edit source]

The most superficial layer (Figure 5) of the pelvic floor muscles consists of:[1][13]

  • Bulbocavernosus and ischiocavernosus:
    • These muscles assist with clitoral function during arousal and climax[1]
  • Superficial transverse perineal muscles (paired):
    • Provide additional support for the urogenital diaphragm
  • External anal sphincter:
    • A circular, layered muscle that closes off the anal canal

The perineum (perineal body) and superficial transverse perineal muscles divide into two triangles:[3]

  • Anterior triangle (called the urogenital triangle):[14]
    • Makes up the anterior half of the perineum, which is diamond shaped
    • The corners of the triangle are the pubis symphysis anteriorly and the ischial tuberosities anterolaterally
  • Posterior triangle (called the anorectal triangle):[15]
    • Makes up the posterior half of the perineum
    • The corners of this triangle are the tip of the coccyx posteriorly and the ischial tuberosities anterolaterally

Physiology of the Pelvic Floor[edit | edit source]

The pelvic floor muscles are, in many respects, just like any other skeletal muscle group:[1]

  • They can contract and relax
  • Be shortened or lengthened
  • Be weak or strong
  • Be stiff or supple
  • They can hold tension or move dynamically
  • May be coordinated or lack coordination - either individually or in relation to other muscle groups
  • Can be normally regulated or “dysregulated”

The pelvic floor muscles contain both fast- and slow-twitch fibres. Slow-twitch fibres make up 70 percent of the pelvic floor.[1][16]

The high prevalence of slow-twitch fibres means that these muscles are able to maintain a degree of resting activation. They are, therefore, considered to be postural muscles.[17][18] This resting activation also enables the maintenance of continence.[1][19]

The fast-twitch fibres allow the muscles to contract voluntarily when necessary (e.g. during an expected or unexpected increase in intra-abdominal pressure).[1][20]

The Nine S's of Pelvic Floor Muscle Physiology[edit | edit source]

While some authors discuss the Five S's,[21] Ibukun Afolabi describes Nine S's:[1]

  • Support[22]
  • Sexual arousal and orgasm[1]
    • The superficial pelvic floor muscles cause engorgement and erection of the clitoris during arousal. The pelvic floor muscles also contract and relax rhythmically during climax
  • Sphincter action[1]
    • Sphincters are circular muscles - when they they contract, they close off a space / lumen
    • They have a certain degree of resting tone, which is regulated by the nervous system
    • They can also be actively contracted
    • They maintain continence[23]
  • Stability[18]
    • The pelvic floor muscles play a key role in the inner core system (i.e. the deepest muscle layer surrounding the abdominal and pelvic cavities, which consists of transversus abdominis, multifidus, the respiratory diaphragm, and the pelvic floor)[1]
  • Synergy[1]
    • The pelvic floor works synergistically with other muscles and organs (see videos below)
    • Relationship with the diaphragm (functions like a piston)[24]
      • On inhalation the diaphragm contracts and flattens, which pushes the viscera inferiorly - the pelvic floor absorbs this movement by eccentrically contracting
      • On exhalation, the diaphragm and pelvic floor return to their starting position
    • The glottis above controls the passage of air in / out of the respiratory passages
    • It works synergistically with the pelvic floor and diaphragm[25]
  • Spring[1]
    • The pelvic floor needs to be able to lengthen under pressure (especially when this pressure is unexpected, such as during a sneeze, or when a high load is applied)
  • Sump pump[1][21]
    • The rhythmic movement of the pelvic floor muscles creates a pumping action that helps to move both blood and lymph through the vascular system, which decreases pelvic congestion / swelling
  • Stretch[1]
    • During labour the pelvic floor muscles must be able to stretch
    • The pelvic floor muscles can reach a stretch ratio of 3.26 by the end of the second stage of labour[26]
    • The levator ani muscles stretch more than 200 percent beyond what is considered the threshold for a stretch injury during the second stage of labour[27]
  • Somatic[1]
    • Refers more to the “state of being” of the pelvic floor at any given time rather than a specific function of the pelvic floor
    • The “somatic reality” of the pelvic floor can provide insight into the relationship between mind, body, brain, and behaviour

References[edit | edit source]

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 Afolabi I. Overview of Female Pelvic Floor Muscle Anatomy and Physiology Course. Plus , 2021.
  2. Scarr G. Biotensegrity: what is the big deal? J Bodyw Mov Ther. 2020;24(1):134-7.
  3. 3.0 3.1 3.2 Chaudhry SR, Nahian A, Chaudhry K. Anatomy, Abdomen and Pelvis, Pelvis. [Updated 2021 Aug 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482258/
  4. Geeky Medics. Pelvic Floor Anatomy (3D Anatomy Tutorial). Available from: https://www.youtube.com/watch?v=I87G1dUcZng [last accessed 5/12/2021]
  5. Continence Foundation of Australia. Female pelvic floor muscle - 3D animation. Available from: https://www.youtube.com/watch?v=q0_JAoaM6pU&t=55s [last accessed 6/12/2021]
  6. Stoker J. Anorectal and pelvic floor anatomy. Best Pract Res Clin Gastroenterol. 2009;23(4):463-75.
  7. Eickmeyer SM. Anatomy and physiology of the pelvic floor. Physical Medicine and Rehabilitation Clinics. 2017;28(3):455-60.
  8. White TD, Black MT, Folkens PA. Chapter 11 - pelvis: sacrum, coccyx, and os coxae. In: White TD, Black MT, Folkens PA editors. Human Osteology (Third Edition). Academic Press. 2012. p219-40.
  9. McEvoy A, Tetrokalashvili M. Anatomy, Abdomen and Pelvis, Female Pelvic Cavity. [Updated 2021 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538435/
  10. 10.0 10.1 10.2 Herschorn S. Female pelvic floor anatomy: the pelvic floor, supporting structures, and pelvic organs. Rev Urol. 2004;6 Suppl 5(Suppl 5):S2-S10.
  11. A Karunaharamoorthy. Levator ani [Internet]. Kenhub. 2021 [cited 5 December 2021]. Available from: https://www.kenhub.com/en/library/anatomy/levator-ani
  12. Jung J, Ahn HK, Huh Y. Clinical and functional anatomy of the urethral sphincter. Int Neurourol J. 2012;16(3):102-6.
  13. Baramee P, Muro S, Suriyut J, Harada M, Akita K. Three muscle slings of the pelvic floor in women: an anatomic study. Anat Sci Int. 2020;95(1):47-53.
  14. Hacking C. Urogenital triangle [Internet]. Radiopaedia.org. 2021 [cited 10 December 2021]. Available from: https://radiopaedia.org/articles/urogenital-triangle?lang=us
  15. Hacking C. Anal triangle [Internet]. Radiopaedia.org. 2018 [cited 10 December 2021]. Available from: https://radiopaedia.org/articles/anal-triangle?lang=us
  16. Marques A, Stothers L, Macnab A. The status of pelvic floor muscle training for women. Can Urol Assoc J. 2010;4(6):419-24.
  17. Dsingh A., Kaur A. Role of postural control exercises and pelvic floor strengthening exercises on chronic low back pain of women with sitting jobs. In: Rebelo F, Soares M editors. Advances in ergonomics in design. Vol 955. Cham: Springer, 2020. p775-82.
  18. 18.0 18.1 Hodges PW, Sapsford R, Pengel LH. Postural and respiratory functions of the pelvic floor muscles. Neurourol Urodyn. 2007;26(3):362-71.
  19. Swash M, Petros P. The pelvic floor: neurocontrol and functional concepts. In: Santoro GA, Wieczorek AP, Sultan AH editors. Pelvic floor disorders. Cham: Springer, 2021. p57-70.
  20. Raizada V, Mittal RK. Pelvic floor anatomy and applied physiology. Gastroenterol Clin North Am. 2008;37(3):493-vii.
  21. 21.0 21.1 Thomas K. Pelvic Floor training for stress urinary incontinence: an update. Co-Kinetic Journal. 2019;(79):14-23.
  22. Peng Y, Miller BD, Boone TB, Zhang Y. Modern theories of pelvic floor support: a topical review of modern studies on structural and functional pelvic floor support from medical imaging, computational modeling, and electromyographic perspectives. Curr Urol Rep. 2018;19(1):9.
  23. Bharucha AE. Pelvic floor: anatomy and function. Neurogastroenterol Motil. 2006;18(7):507-19.
  24. Hwang UJ, Lee MS, Jung SH, Ahn SH, Kwon OY. Effect of pelvic floor electrical stimulation on diaphragm excursion and rib cage movement during tidal and forceful breathing and coughing in women with stress urinary incontinence: A randomized controlled trial. Medicine (Baltimore). 2021;100(1):e24158.
  25. Rudavsky A, Turner T. Novel insight into the coordination between pelvic floor muscles and the glottis through ultrasound imaging: a pilot study. Int Urogynecol J. 2020;31(12):2645-52.
  26. Ashton-Miller JA, Delancey JO. On the biomechanics of vaginal birth and common sequelae. Annu Rev Biomed Eng. 2009;11:163-76
  27. Iglesia CB, Smithling KR. Pelvic organ prolapse. Am Fam Physician. 2017;96(3):179-85.
  28. JULIE WIEBE. The Diaphragm Pelvic Floor Piston Demo. Available from: https://www.youtube.com/watch?v=mLFfZfm7O7c [last accessed 5/12/2021]
  29. FemFusion Fitness and Pelvic Health. Can Singing Heal Your Pelvic Floor? The Pelvic Floor-Glottis Connection. Available from:https://www.youtube.com/watch?v=4dS7bc_4Mx0 [last accessed 5/12/2021]