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Pelvic floor muscles

Pelvic floor muscles require both slow and fast twitch fibres to work. Explore the interrelationship between pelvic floor and abdominal muscles.

The pelvic floor muscles are made up of slow and fast twitch fibres. It requires the combination of both slow and fast twitch fibres for the pelvic floor to work. It is also important to also understand the interrelationship between pelvic floor and abdominal muscles.

The are three main components of the pelvic floor:

  • Levator ani muscles
  • Coccygeus muscles – these muscles assist the levator ani muscles in supporting the pelvic organs
  • Fascia covering the muscles

In this step we will focus on the levator ani muscles: the puborectalis; the pubococcygeus and the iliococcogeus muscles as illustrated in the figure below (repeated from the previous step).

Levator ani muscles

Figure 2.6: ‘Bird’s eye view’ of the pelvic floor muscles of a female.

Levator ani muscles

The main levator ani muscles form the largest component of the pelvic floor, they are innervated by the pudendal nerve S2-S4.

The levator ani is divided into three parts:

  1. Puborectalis is a U-shaped sling, its contraction bends the anal canal and creates the ano-rectal angle (90 degrees) where the rectum meets the anus (we will be looking at this in greater depth in week 4: Bowel function and disfunction bowel continence). Puborectalis is a thick muscle and its main function is to maintain continence. During defaecation it relaxes to straighten the anal canal and allow passage of feaces.

  2. Pubococcygeus muscle controls urine flow and contracts during orgasm. For males it assists in ejaculation and for females it aids in childbirth and core stability. A strong pubococcygeus muscle helps to maintain urinary continence and the proper positioning of the baby’s head at childbirth.

  3. Iliococcogeus muscle – this muscle acts as an ‘elevator’ of the pelvic floor and anorectal canal.

During the second phase of labour the levator ani muscles and/or the pudendal nerve are at a high risk of damage. The Pubococcygeus and Puborectalis are most prone to damage due to their position. 

Pelvic floor muscle fibres

Muscles are made up of slow and fast twitch fibres.

It requires the combination of both type 1 red slow and type 2 white fast twitch fibres for the pelvic floor to work.

An understanding of this is important for effective teaching of pelvic floor muscle exercises (which we will be looking at in greater depth in Week 6: Promoting Bladder and Bowel Continence).

Clinical practice points. Differences between fibre types
Type 1 – red: slow twitch fibres Type 2 – white: fast twitch fibres
Rich in blood supply Quick reacting
Large capillary bed Work fast
Sustains contraction over time Fatigue quickly
Contracts 10 – 20 times/second Contracts 30 – 60 times/second
Tone is affected by age and trauma (childbirth, heavy lifting, obesity, hormone changes, abdominal surgery) Contract spontaneously with significant force with an increase in abdominal pressure (cough, laugh, sneeze, jump) in order to equalise the bladder and urethral pressure to maintain continence
Strength training exercise: slow pelvic floor contractions give support to the pelvic floor. Slow twitch fibres need to be worked daily to maintain tone ’The knack’ exercise: fast pelvic floor contraction tightens the urethral sphincter and inhibits bladder contractions

Inter-relationship between pelvic floor and abdominal muscles

It is important to also understand the interrelationship between pelvic floor and abdominal muscles.
When abdominal muscles are contracted strongly the entire pelvic floor contracts in response. This is known as co-contraction.
This co-contraction is important when assessing the pelvic floor and teaching pelvic floor exercises because abdominal muscle activity can help to indicate pelvic floor activity.
Position of the abdominal muscles Figure 2.7: Position of the abdominal muscles.
When abdominal muscles are contracted gently the pelvic floor responds in a specific way:
  • Pubococcygeus contracts with the transversus
  • Iliococcogeus contracts with the obliques
  • Puborectalis contracts with rectus abdominis

Your task

The following are all functions of the pelvic floor:
  • Supports the pelvic organs
  • Reinforces urethral closure during increased intra-abdominal pressure
  • Maintains the ano-rectal angle
  • Provides rectal support during defaecation
  • Assists in pelvic spinal stability
  • Contributes to sexual arousal and performance
  • Maintains continence
  • Contraction of the pelvic floor inhibits urgency

Is one of these functions more important than the others?

Hint – think about function with a healthy pelvic floor and also if there is a pathology.

© Association for Continence Advice. CC BY-NC 4.0
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Understanding Continence Promotion: Effective Management of Bladder and Bowel Dysfunction in Adults

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