Pelvic floor 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).

^{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

Inter-relationship between pelvic floor and abdominal muscles

^{Figure 2.7: Position of the abdominal muscles.}

• Pubococcygeus contracts with the transversus
• Iliococcogeus contracts with the obliques
• Puborectalis contracts with rectus abdominis

Your task

• 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.