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

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.

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 textCross 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.