Muscles of the Trunk - Townsville Massage

On the back of the body, the trunk muscles are built in layers, and as a group they help stabilise the trunk and protect to the spinal cord.  They hold the body upright while extending and rotating the neck and trunk.  The many muscles throughout the back are named because of the actions they perform… like the Erector Spinae for spinal extension and rotators for spinal rotation.

They can also be named for their origin and insertion point, like the Semispinalis Thoracis which has its origin on the transverse process of the Thoracic Vertebrae and inserts on the spinous process of the Thoracic Vertebrae.  The Quadratus Lumborum covers the area of your kidneys, and is involved in side bending.
Those on the front of the body are collectively known as the abs.  Actually there are a few different abdominal muscles that work together.  The Rectus Abdominis is known as the “six pack”.  It flexes the trunk so that the rib cage moves toward the pelvis, and covers the Transverse Abdominis, which is responsible for keeping your internal organs just that… internal.

Rectus-AbdominusRectus Abdominus.

The Rectus Abdominus is the most superficial of the abdominal muscles. It is this muscle which forms the six-pack shape!
It is a key postural muscle and is responsible for flexing the lumbar spine, as when doing a “crunch”.  The Rectus Abdominis assists with breathing and plays an important role in respiration.

It runs vertically on each side of the anterior wall of the abdomen and controls the tilt of the pelvis and curvature of the lower spine.

Action:

  • It flexes trunk and lumbar spine, aids forced expiration and raise intra-abdominal pressure.
  • It also tilts pelvis forward improving the mechanical positioning of the Erector Spinae.

Typical use:

  • Moving from lying to sitting.

external-obliqueExternal Obliques.

Your External Obliques run diagonally down from your lower eight ribs, attaching to the top half of your hip and your Rectus Abdominis.

The External Obliques, along with the Internal Obliques, are the rotators among the muscles that make up your abdominal muscle anatomy. They twist your body at the waist and straighten your body when you bend to the side.

Action:

  • Supports abdominal wall, assists forced expiration, aids raising intra-abdominal pressure and, with muscles of opposite side, abducts and rotates trunk.
  • Contraction of one side alone laterally bends the trunk to that side and rotates the trunk to the other side. It also compresses the abdomen and supports the abdominal organs.

Typical use:

  • Raking leaves.
  • Mopping the floor.

Internal-ObliqueInternal Obliques.

The Internal Obliques are under the External Obliques and run diagonally in the opposite direction.  The Internal Obliques work with the externals to rotate the trunk. They will also compress the abdomen when both sides contract.

It’s the same with the External Obliques, but unlike the External Obliques, they are not visible when fully developed.

Action:

  • Supports abdominal wall, assists forced respiration, aids raising intra-abdominal pressure and, with muscles of other side , abducts and rotates trunk. Conjoint tendon supports posterior wall of inguinal canal.
  • Contraction of one side alone laterally bends the trunk to that side and rotates the trunk to the other side. It also compresses the abdomen and supports the abdominal organs.

Typical use:

  • Raking leaves.
  • Mopping the floor.

Transverse-AbdominusTransversus Abdominus.

Of the four muscles of the abdominal muscle group, the Transverse Abdominis is the one that does not cause trunk movement.  When you “suck it in,” it’s muscle that pulls the ab wall in.  It is located deep in your abdomen, underneath your obliques. It holds your organs in place and forces expiration when contracted.

This muscle is often mistakenly overlooked, because with training, it can pull your stomach in, giving you a slender appearance.

Action:

  • Supports abdominal wall and organs, aids forced expiration and raising intra-abdominal pressure. The conjoint tendon supports posterior wall of inguinal canal.

Typical use:

  • Maintaining good posture.

Quadratus-LumborumQuadratus Lumborum.

The Quadratus Lumborum is a muscle with many functions.  It laterally flexes (sidebends) the trunk, and elevates the hip. It also helps to stabilise the low back, and is usually involved when low back pain is present.

It has fibers that run vertically and in two diagonals.

The Quadratus Lumborum act as guy ropes for the thoraco lumbar junction and lower ribs to the pelvis.  Due to abnormal stress patterns, mainly through poor posture, one or both of these will be chronically or acutely contracted, tender to touch and a common cause of lower grade back pain.  Pain is felt mainly locally and stimulates pain coming from the kidneys.

Action:

  • Fixes 12th rib during respiration and lateral flexes (side-bends) trunk.

Typical use:

  • Bending sideways to pick something up.

Erector-SpinaeErector Spinae.

The Erector Spinae is often described as a group of different muscles called Iliocostalis, Longissimus and Spinalis.

Erector Spinae consists of lots of small fibres which are situated very close to the spine.
They are the chief flexors of the vertebral column. They straighten the flexed column and can also bend it posteriorly. They also release during its flexion so that the movement is slow and controlled.

Actions:

  • Extension of the spine.
  • Lateral flexion (side-bending) of the spine.
  • Maintains correct curvature of the spine.

Typical use:

  • Maintaining good posture.

SpleniusSplenius.

Splenius is often divided into two muscles, Splenius Capitus which insert on the skull, and Splenius Cervicis that inserts onto the cervical transverse processes of the spine.
The two flat muscles extend from the upper vertebrae to the base of the skull and help to rotate, flex or extend the head and neck.

Actions:

  • Extension of the head and neck.
  • Contraction of one side laterally flexes and rotates the neck to the same side.

Typical use:

  • Looking up at the stars.
  • Looking over your shoulder.

MultifidusMultifidus.

Multifidus is a series of small muscles which travel up the length of the spine. It is an important muscle in the rehabilitation of lower back pain and can have an extraordinary impact on your body.
Although the Multifidus muscle is very thin, it’s a “powerful” muscle that provides support to the spine.  Multifidus muscle is a series of muscles that are attached to the spinal column.

The Multifidus muscles help to take pressure off the vertebral discs so that our body weight can be well distributed along the spine.  It also keeps our spine straight while the deep muscle group contributes significantly to the spines stability. These two groups of multifidus muscles are recruited during many actions in our daily living, which includes bending backward, sideways and even turning our body to the sides.

Studies have shown that the multifidus muscles get activated before any action is carried out so to protect our spine from injury.  When you are about to carry an object… even before moving your arm, the Mutifidus muscles will start contracting before to the actual movement of the body and the arm to prepare the spine for the movement and prevent it injury.

Actions:

  • Extension, lateral flexion and rotation of the spine.

Typical use:

  • Maintaining good posture of the spine.