I. Alignment & Balance of the Human Body. Midline Anatomy & the Median Plane.

by leggi 3mo22nd Aug 20193 min read5 comments


What do balance and alignment mean with respect to the human body?

This is an introduction piece for my Base-Line Hypothesis of Human Health and Movement. The anatomical information presented should be easily verifiable.

Alignment and Balance.

Two (of the many) definitions for balanced:

1. Different parts of something that exist in equal or correct amounts.
2. A state of equilibrium, being in harmonious arrangement.

Alignment has many definitions, the two I feel most relevant to 'body alignment' are:

1. Arrangement in a straight line.
2. Arranged in the correct relative positions.

The Median Plane.

The median plane (also known as the midsagittal plane) is the plane that splits the body into left and right halves.

A straight line when viewed from the front or back.

A 2D shape from the side.Image text.

The body must be "correctly arranged" to create the median plane, where:

  • The body is aligned.
    • All midline anatomy is arranged on the straight line of the median plane.
  • The body is balanced.
    • Left and right sides are in equilibrium, either side of the median plane.

The position of the rest of the body should be considered relative to the midline anatomy and the median plane.

Midline Anatomy.

Palpable Anatomical Structures.

Some easy to find midline anatomical structures include the:

  • Anus.
  • Pubic symphysis of the pelvis.
  • Navel.
  • Xiphoid process of the sternum.
  • Jugular notch of the sternum.
  • External occipital protuberance at the base of the skull.

Linear Midline Structures.

The linear structures I believe we should focus on for body alignment are:

  • The linea alba. Midline at the anterior (front) of the body. Our primary anatomical guide for body alignment.
  • The nuchal ligament and supraspinous ligament. Midline at the posterior (back) of the body. Our secondary anatomical guides for body alignment.

Image text

Linea Alba.

The linea alba (Latin for 'white line') is a strip of strong connective tissue midline at the front of the abdomen. One end attaches to the pubic symphysis of the pelvis and the other end to the xiphoid process of the sternum.

. Image text

The linea alba is formed from the aponeuroses (tough, thin sheets of connective tissue) of the three lateral abdominal muscles (the external abdominal oblique, internal abdominal oblique and transversus abdominis) as left and right sides meet at the front of the abdomen. Image text' Cross section of anterior abdomen.

Before the aponeuroses of the lateral abdominal muscles merge at the linea alba they form the left and right rectus sheaths (tunnels of connective tissue) in which the corresponding left and right rectus abdominis muscles lie. The rectus abdominis muscles are the closest muscular tissue to the linea alba, lying either side from pelvis to chest.

The linea alba and rectus abdominis both originate from the pubic symphysis.

Nuchal and Supraspinous Ligaments.

The nuchal ligament (ligamentum nuchae) and supraspinous ligament are one continuous structure at the posterior of the spine, a long strip of tough connective tissue from "head to tail". Image text

The nuchal ligament is a septum (dividing wall) midline in the back of the neck. It consists of fibro-elastic connective tissue.

The nuchal ligament attaches to the base of the skull at the external occipital protuberance (feel for the midline bump at the back of the skull) and the medial nuchal line (a.k.a. the external occipital crest).

The nuchal ligament then attaches to the spinous processes of all the cervical vertebrae. At the 7th (last) cervical vertebra, the nuchal ligament continues as the supraspinous ligament, a strong, fibrous cord attaching to the spinous processes of the seventh cervical vertebra, all twelve thoracic vertebrae and the upper lumbar vertebrae, usually terminating at L4 (but possibly L3 or L5).

The left and right trapezius muscles meet midline, attaching to the nuchal and supraspinous ligaments from the base of the skull to the last thoracic vertebra.

. Image text

Unimportant to my hypothesis, I mention it now to be complete: The anterior longitudinal ligament is the longest anatomical structure on the midline. Running the entire length of the spine and attaching to the anterior of each vertebrae, it cannot be 'felt', either by palpation or by focusing on adjacent muscles.

Increasing Conscious Awareness of Midline.

To increase conscious awareness of our midline we can tap into the proprioceptive information generated by various structures by actively focusing on them.

Muscles and other structures that are on, or either side of, midline include:

  • The pelvic floor muscles. A group of muscles at the base of the linea alba, left and right sides meeting as a crescent shape on midline.
  • Perineal muscles. Anal sphincter.
  • The clitoris/suspensory ligament of the penis located at the pubic symphysis.
  • The rectus abdominis muscles either side of the linea alba.
  • The trapezius muscles attaching to the nuchal and supraspinous ligaments.

Much information about the relative positioning the head can be gained from:

  • Nostrils. Feel the air flow in each nostril, aiming for balance.
  • Movement of the mouth, lips and jaw.
  • The tongue. Positioning the tongue behind the central incisors and on the hard palate provides sensory feedback about midline.

Dynamic Alignment and Balance.

The body is not static. Balance and alignment are dynamic states.

Working on the premise "a full range of natural movement" is a good thing (more here). and I'm still working on the wording:

When the body has a full range of natural movement, the linea alba and nuchal/supraspinous ligaments can be arranged in a straight line on the median plane (when viewed from the front or back) - this is maximally extended alignment.

For the body to be able to move through its full range of natural movement our midline anatomy needs remain in the correct relative positions, aligned so that the rest of the body can extend fully away from midline. Like a rope that can bend and flex without tensions pulling it off alignment .

Dynamic alignment and balance:
Our midline anatomy is ideally arranged to permit a full range of movement.
Balance and alignment are maintained through a full range of natural movement.

Think about where your anatomy is in relation to the median plane. Feel for your alignment.

Part 2: The Main Muscles of Movement, Dynamic Alignment & Balance.