BACK: ANATOMY AND PHYSIOLOGY

by Ben Fazio

The back is a complex structure providing rigid support and a protective, bony sheath to the central nervous system. Coupled with numerous muscles it is capable of bearing significant forces, as well as flexing and extending through a remarkable range of movements.

The back consists of the entire posterior, or rear, of the body from the neck to the buttocks and it is divided into four functionally discrete regions: the cervical spine, thoracic spine, lumbar spine and sacral spine.

SPINAL COLUMN

The cervical spine is found in the neck and contains seven vertebrae referenced as C1 through C7. The cervical spine has three essential skeletal functions:

  1. it supports the weight of the skull;
  2. C1 the Atlas and C2 the Axis form the joint connecting the skull and spine. These bones are specialised to allow a greater range of motion than normal vertebrae and are responsible for the nodding and rotation movements of the head; and
  3. vertebrae C6 and C7 permit the flexion and extension of the neck and head.

The thoracic spine is made up of 12 vertebrae (T1 through T12). Th is structure is capable of very little motion, as it is primarily protective. In the lower back you find the lumbar spine. It is responsible for the support of the torso when the body is upright, and allows lumbar muscles to bend, extend, and rotate the body at the waist. T e sacral vertebrae are found at the base of the spine in the pelvis. Here you find fused bones in the sacroiliac bone and the coccyx.

Correct function of the spine allows for extension, flexion and rotation of individual vertebra and this allows for optimal movement in the sagittal, frontal and transverse planes of the body. The primary purpose of the extensor muscles is to support the back when the body is in an upright position and to provide support and stability as antagonist muscles during fl exion of the trunk. Th e back extensor muscles are used as primary movers when you lift objects from the ground and put you in an upright position. Th e erector spinae, a pair of muscles set on either side of the lumbar spine, and the gluteal muscles, located in the buttocks and upper thighs, are the most prominent of the extensors.

The flexors are the muscles located on the anterior (front) of the spine. These muscles permit the body to flex in all directions, with particular importance to the motions of bending forward, lifting, and the arching of the lumbar (low back) spine. The flexor muscles include the abdominal muscles.

The oblique muscles are on the medial, or middle, of the spine. These muscles are necessary in the rotation of the spine as well as in the maintenance of proper posture.

DEEP MUSCLES OF THE BACK

The transversospinalis muscles consist of three layers, the deepest being the rotatores, then the multifi dus and fi nally the semispinalis being the most superficial. These muscles provide precise movements of each vertebra and aid stability in the back.

The erector spinae muscles are more superfi cial and larger than the transversospinalis muscles and originate from lumbar fascia. Th ree groups of muscles make up this group:

  1. the iliocostalis which is the most lateral (outer) and attaches to the ribs, close to their attachment to the spine;
  2. the longissimus originates from the lumbar fascia and inserts to the transverse processes of the vertebrae; and
  3. the spinalis is the most medial (central) muscle and it attaches to the lumbar and thoracic spinous processes.

All of these muscles are responsible for extending the spine (leaning backwards).

SUPERFICIAL MUSCLES OF THE LOWER BACK

There are several large muscles in the lower back:

  1. The latissimus dorsi is a triangular, flat muscle, which covers the lumbar region and the lower half of the thoracic region. It makes up some of the armpit and stretches down to the gluteus. Th is is the largest muscle of the lower back responsible for pulling the arm downwards and backwards. It originates from the spinous processes of T6-T12 and the Iliac crest (top of the pelvis) and travels upwards across the entire lower back. Th e muscle belly twists before it inserts onto the humerus (upper arm bone). Any action that brings the arm down to the trunk ( lat pull downs) or lift s the trunk up to the elbow ( chin ups) involves significant activation of this muscle.
  2. The quadratus lumborum is responsible for side bending and also aids extension of the lumbar spine. It originates at the Iliac crest and passes upwards to attach to the lowest rib and to the transverse processes of L1- L4. Th is is a deep muscle and is not easily palpated.

“Great ways to cross-train for proprioceptive adaptation include activities that require balance, coordination, agility and power, and movements that challenge a person’s normal range of motion.”

SUPERFICIAL MUSCLES OF THE UPPER BACK

There are several large muscles in the upper back:

  1. The trapezius is a large superficial muscle which extends longitudinally from the occipital bone to the lower thoracic vertebrae, and laterally to the spine of the scapula (shoulder blade). The trapezius has three functional regions: The superior region (descending part) supports the weight of the upper limb. The intermediate region (transverse part) retracts the scapulae. Th e inferior region (ascending part) medially rotates and depresses the scapulae.

The two trapezius muscles together resemble a trapezium, or diamond-shaped quadrilateral. Th e four points of the diamond are: the head (at the occipital protuberance), the two shoulders, and the middle of the back (at the spinous process of the twelft h thoracic vertebra, T12).

  1. The rhomboid major is a muscle on the back that connects the scapula with the vertebrae of the spinal column. Th is muscle originates from the spinous processes of the thoracic vertebrae T2 to T5 as well as the supraspinous ligament. It inserts on the medial border of the scapula, from about the level of the scapular spine to the scapula’s inferior angle. The rhomboid major is considered a superficial back muscle, deep to the trapezius, and is located directly inferior to the rhomboid minor.

The rhomboid major helps to hold the scapula (and thus the upper limb) onto the ribcage. It also acts to retract the scapula, pulling it towards the vertebral column, and downwardly rotates the scapula with respect to the glenohumeral joint. Both collectively with levator scapulae elevate the medial border of the scapula. Th is muscle stabilises the scapular and helps provide the correct functional movement of rotating the scapular when the arm is elevated. Th is muscle must work together with the trapezius muscle.

BACK MUSCLES & PROPRIOCEPTION

Flexion, extension and rotation of the trunk involve proprioception and kinesthetic awareness of where the trunk and limbs are in relation to space and time. Th rough conscious appreciation and cognitive processing of the body’s position in space, the central nervous system and sensory receptors can be conditioned to be more responsive to length and tension in the muscles and tendons.

Proprioceptive adaptation requires all of the core muscles including the deep muscles of the back to be functional. Great ways to cross-train for proprioceptive adaptation include activities that require balance, coordination, agility and power, and movements that challenge a person’s normal range of motion.

BACK EXERCISES

LATISSIMUS DORSI

  • Close-grip pulldowns
  • Wide-grip front pulldowns
  • One-arm dumbell rows
  • Seated cable rows
  • Chin-ups
  • Bent-over barbell rows
  • Deadlifts
  • Wide-grip pull-ups
  • Stiff -arm pushdowns

ERECTOR SPINAE

  • Hyperextensions
  • Deadlifts
  • Good mornings

RHOMBOIDS (MAJOR AND MINOR)

  • Close grip pulldowns
  • Wide-grip front pulldowns
  • One-arm dumbell rows
  • Bent-Over lateral raises
  • Seated cable rows
  • Bent-over barbell rows
  • Wide grip pullups
  • Chin-ups

TRAPEZIUS

  • Bar Bell shrug
  • Upright row

Written by: Ben Fazio

Website
http://www.mhts.com.au
Profile
EXERCISE PHYSIOLOGIST Ben Fazio MAAESS, Director Melbourne Health Training Services Exercise physiology, personal training and massage. Biomechanical video analysis of all sports and specialist bicycle fitting. More details at www.mhts.com.au