
Updated: 23 April 2009

The Core of Our Body

The human body can be divided into two distinct parts:
The three body weights of the torso - head, chest, and pelvis - are connected via the spine and supported by the large muscle groups of the upper back, abdomen, and pelvis. The main function of that part of the skeletal system is to protect the delicate internal organs. The main function of that part of the muscular system is to support the back, improve and help maintain posture and aid the spinal muscles with movement of the torso.

The limbs - arms and legs - attach to the torso in joints with a large range of motion (shoulder and hip joint respectively). Their main function is locomotion - moving through space.

The Spine - Backbone of Our Core Support

The spine is one of the most important parts of our body. Without it, we could not keep ourself upright or even sit up. It gives our body structure and support and carries the substantial weight of our head. It allows us to move about freely and to bend with flexibility. The spine is also designed to protect our spinal cord. The spinal cord is a column of nerves that connects our brain with the rest of our body, allowing us to control our movements. Without a spinal cord, we could not move any part of our body, and our organs could not function. This is why keeping our spine healthy is vital if we want to live an active life.

The spine is a flexible column made up of cylindrical bones called vertebrae that are stacked on top of each other. These vertebrae are linked and hinged together by facet joints, which give them the flexibility to move against each other. Openings within each vertebra, (vertebral foramina), line up in succession to form the long hollow vertebral canal for the spinal cord. These openings also allow nerves from the spinal cord to branch out and exit the side of the spinal column. When you run your finger down someone's back you can feel the spinous process of the vertebra through the skin.

In between the vertebra are intervertebral discs, soft, gel-like cushions that keep the bones from rubbing against each other, increase spinal flexibility and absorb shock from everyday movements. Sometimes, part of the inner softer part of the disc (the nucleus pulposus) bulges out (herniates) through a weakness in the outer part of the disc. The bulging disc may press on nearby structures such as a nerve coming from the spinal cord. Some inflammation also develops around the prolapsed part of the disc. The pain caused by such a prolapsed or herniated disc (commonly called a 'slipped disc'), is often severe, and usually comes on suddenly. The pain is usually eased by lying down flat, and is often made worse if you move your back, cough, or sneeze. Any disc in the spine can prolapse. However, most prolapsed discs occur in the lumbar part of the spine (lower back).

When the prolapsed disc presses on a nerve coming from the spinal cord, you may feel pain along the course of the nerve in addition to back pain. Therefore, although the problem is in the back, you may feel pain down a leg to the calf or foot, often worse than the back pain. With a prolapsed disc, the sciatic nerve is the most commonly affected nerve. (The term 'sciatica' means nerve root pain of the sciatic nerve.) The sciatic nerve is a large nerve that is made up from several smaller nerves that come out from the spinal cord in the lower back. It travels deep inside the buttock and down the back of the leg. There is a sciatic nerve for each leg.


	Vertebrae are stacked on top of each other in a flexible column to form the spine. The normal spine has an "S"-like curve when looking at it from the side. This allows for an even distribution of weight. The "S" curve helps a healthy spine withstand all kinds of stress.
	The 7 smaller vertebrae of the cervical spine form a slightly inward curve. They support the skull and allow for its rotation.
	The 12 medium sized vertebrae of the thoracic spine each have a pair of ribs attached and curve outward. In the front part of the body the ribs attach directly or indirectly to the sternum, thus forming the rib cage which allows for only limited movement. The rib cage protects the chest cavity and holds the heart and lungs.
	The 5 larger vertebrae of the lumbar area curve inward. The lumbar spine carries the most weight and experiences the most motion relative to other regions of the spine. These two factors make the lumbar spine the most frequent source of back pain. Even though the lower portion of the spine holds most of the body's weight, each segment relies upon the strength of the others to function properly.
	Below the lumbar spine is the sacrum. The sacrum is actually a group of specialized vertebrae that connects the spine to the pelvis. During development (those nine months before birth), these vertebrae fuse (grow together) creating one large "specialized" vertebral bone that forms the base of your spine and at the same time the "back wall" of your pelvis. The sacrum serves to transfer the weight of the upper body to the legs. The nerves that leave the spine in the sacral region control the bowel and bladder functions and give sensation (feeling) to the crotch area.
	Joined to the sacrum by a flat, circular layer of fibrocartrilage (a strong type of tissue) is the coccyx. The coccyx is all that is left of the tailbones of animals at this point in our evolution. At birth, the coccyx is made up of up to four separate small bones, but they join together by age 60, as if they were one bone. The coccyx bones of men join together at an earlier time than women's.

Deep back muscles are arranged in several layers, with the deepest ones consisting of small bundles passing from one vertebra to its neighbour. Different layers span two, three, and more vertebral levels. The smaller, deepest ones are sometimes referred to collectively as the multifidus, superficial to them the erector spinae is a group of longer, bigger muscles.

The Chest and Shoulder Girdle

The 12 thoracic vertebrae each have a pair of ribs attached. In the front part of the body 7 of the rib pairs attach directly (true ribs) and 5 indirectly (false ribs) to the main body of the sternum, thus forming the rib cage. The lowest two rib pairs are called floating ribs because they have no cartilaginous attachments to the sternum.

The shoulder girdle supports the upper limbs and is found at the top part of the rib cage:
On the front of the rib cage, running horizontally between the top part of the sternum (manubrium) and scapula, is the clavicle, or collarbone. It is a slender bone with two bends in it, so that it has an elongated S shape. Its main function is to transmit forces from the arm to the thorax.
In the back on either side of the rib cage sits a scapula, or shoulder blade. This is a broad, somewhat triangular bone that is attached to the rib cage muscularly (serratus anterior). It features two processes, the acromion process and coracoid process, that fashion a shallow socket (glenoid cavity) into which the head of the humerus articulates. The various borders, angles, ridges and processes of the scapula offer much surface for muscle attachments.

The Serratus anterior (see image on right) originates on the surface of the upper nine ribs at the side of the chest, and inserts on the costal aspect of the whole length of the medial border, i.e., "rib side of the inner edges" of the scapula. Imagine a sandwich: the ribs and scapula would be the bread, and the serratus anterior would be the spread in between, with some of it squeezing out down and sideways towards the arm side. Its function is to stabilize the scapula on the ribcage, and to move them away from each other and the thoracic vertebrae of the spine. It is used strongly when doing push-ups, working together with the Pectoralis minor, a muscle on the front of the chest.

The Trapezius is a diamond-shaped muscle that covers the large area from the neck down to the 12th thoracic vertebra and from the spine to the ridge of the shoulder blade and lateral end of the clavicle. The fibers of different sections run in different directions and have lightly different functions, but as a whole, the trapezius rotates the scapula, and also helps to stabilize the scapula on the ribcage, especially when the arm is raised overhead.

The Latissimus dorsi is a large, triangular muscle covering the middle and lower parts of the back. It originates on the lower six thoracic vertebrae, lumbar vertebrae and back of the sacrum (forming the long side of the triangle), and inserts in a small area at the inner side at the top of the humerus. It is the most powerful humeral extensor, meaning it pulls the arm towards the body.

The Pelvis

The sacro-iliac joint is the area where the spine (sacrum) connects to the pelvic girdle. The ilium, ischium and pubis bones have fused and together with the sacrum form the bowl-shaped pelvis. The upper border of the ilium is the iliac crest, the highest part of the pelvis in the waist area. The iliac crest runs down and forward towards the ASIS, (Anterior Superior Iliac Spine), or hipbone, probably the part of the pelvis most easily identified by people. Another easily recognizable bony landmark is the sitbone, the lowest part of the pelvis. It is also called ischial tuberosity, being part of the ischium, the lower and posterior of the fused pelvic bones. The lower and anterior of the fused pelvic bones is the pubis. Palpatable in the front, "between the legs", connected via the pubic symphysis are the bony landmarks referred to as the pubic bone.

Where the ilium, pubis and ischium have fused laterally, they form a cup-shaped cavity (acetabulum), the socket into which the head of the femur attaches to form the hip joint. The pelvis bears the weight of the upper body, and passes it on to the lower limbs. Conversely, it absorbs stress from the lower limbs during locomotion.

Psoas major arises from the bodies of the lumbar vertebrae, runs anterior to the pelvis and inserts on the top part of the femur. Iliacus arises from the entire internal iliac fossa ("bottom lip" of Iliac crest). In the lower part, its fibers merge with those of psoas and insert on the femur via the same tendon. Because they share the same tendon and have the same action on the thigh, iliacus and psoas are often described as a single muscle (ilio-psoas).

Quadratus lumborum originates from the posterior iliac crest and inserts on rib 12 and the transverse processes of the lumbar vertebrae.

The Pelvic Floor muscles are a group of several small muscles that form a large sling (or hammock) of muscles stretching from side to side across the floor of the pelvis. They attach to the pubic bone in front, and to the coccyx behind thus forming your "undercarriage". The openings from bladder (urethra), bowels (rectum), and, in women, womb (vagina) all pass through the pelvic floor.

Pelvic Floor Muscles; Male, Lateral View

The pelvic floor muscles

support pelvic organs and abdominal contents, especially when standing or during contraction of the transversus abdominis
support the bladder to help it stay closed, actively squeezing when coughing or sneezing to help avoid leakage - when the muscles are not working effectively you may suffer from leaking ("urinary incontinence"), and/or urgent or frequent need to pass urine
are used to control wind and when "holding on" with your bowels
have an important sexual function, helping to increase sexual awareness both for yourself and your partner during sexual intercourse

The Abdominals – The Power House for Our Core Support

Several sets of muscles support the back, improve and help maintain posture and aid the spinal muscles with movement of the torso. They help transfer force between the upper and lower body, and they also protect the delicate internal organs. Keeping our spine healthy is vital if we want to live an active life, and there is a close relationship between our spine health and the strength of our “power house”.

Abdominal Anatomy There are four muscle groups that make up the walls of our abdominal area power house, from the inside out:
	The Transverse Abdominis (“girdle”, or “corset”) is your innermost abdominal muscle and runs horizontally across the abdominal wall and along the midsection. The muscle spans the area from the pelvis and the lumbar region of the spine to the six lower ribs. The transverse abdominis pulls the abdominal wall inward, acts as a natural weight belt, keeps your insides in and assists in breathing (contraction supports expiration, i.e., breathing out). This muscle is essential for trunk stability. Strengthening the transverse abdominis will enhance your posture and may alleviate back pain. The Internal Obliques overlie and run diagonally to the Transversus abdominis (“back pocket”). Simplyfied, they originate on the iliac crest, wrap around the waist and insert on the cartilages of the lower ribs. These muscles protect a weak point in the abdominal wall and work with the external obliques to help twist the torso. The internal obliques aid the trunk in twisting in the same direction as the side they are on.
The External Obliques run in a diagonally opposite direction; basically from the lower ribs along the side of the torso and partly on the front to the rectus and the pubic bone (“front pocket”). These muscles also support the abdominal organ tissue. They aid in the twisting of the trunk, and assist the rectus abdominis muscle in flexing the spine when the trunk twists or turns. The left external oblique is activated when twisting to the right, and the right external oblique is activated when twisting to the left. Activation of external and internal obliques of the same side support the spinal lateral flexion (side-bend). The Rectus Abdominis is the most superficial abdominal muscle and runs vertically along the front of our torso from the pubic bone to the sternum (inserting in the cartilage of the fifth, sixth, and seventh ribs). Activation of the rectus abdominis flexes the spine, pulls the rib cage and the pelvis towards each other and may affect the curvature of the lower back. It also tenses the abdominal wall and aids in compressing the contents of the abdomen. Strengthening the rectus abdominis will provide you with the "six pack" and enhance performance in sports requiring jumping, running, and lifting objects. It does not, however, improve posture, support trunk stability or support the back.

To complete the "house" image:
The Pelvic Floor muscles (images above) are a group of several small muscles that form a large sling (or hammock) of muscles stretching from side to side across the floor of the pelvis. This "undercarriage" basically holds the abdominal organs inside the cavity when our body is upright, or the abdominal cavity is compressed when the transversus abdominis and diaphragm are contracting.

The Diaphragm (see image to right) is the dome-shaped muscle that forms the “roof” of your power house. It attaches to the bottom of the rib cage and separates the chest (thoracic) cavity from the abdomen. The diaphragm is the main muscle of respiration. Contraction of the diaphragm muscle creates a vacuum in the chest cavity and expands the lungs during inspiration (breathing in). We rely heavily on the diaphragm for our respiratory function so that when the diaphragm is impaired, it can compromise our breathing.

The stomach is an organ of the alimentary canal, a muscular tube that forms part of the digestive system. The wall of the stomach contains smooth muscle tissue. Contractions of the smooth muscles of the alimentary canal serve to mix food with digestive juices, and to move the resulting mixture further along (peristalsis). Smooth muscles are called involuntary muscles, because they cannot be consciously controlled. As we have no control over the smooth muscle tissue of the stomach, we cannot consciously contract it, or “exercise” it. Thus, there are no “exercises to strengthen the stomach” or “using the stomach to move the spine”. The term "stomach" therefore does not belong into Pilates class.

Abdominal Physiology

Some of the abdominal muscles support spinal movement (rectus abdominis, external and internal obliques) and can thus be strengthened with exercises that move the spine in flexion, extension, lateral extension, rotation, undulation. Other muscles are more responsible for abdominal support and need to be exercised in a different way (Kegel exercises for pelvic floor muscles, breathing exercises for transverse abdominis and diaphragm). One very effective way to create the overload necessary for muscular growth in those muscles is the vocalizing in forceful expiration, or martial arts yell.

Aside from a cheesy sound effect in a martial arts film a loud, guttural yell has other purposes. A proper yell gives a martial artist more focus and power to perform a movement in proper technique. In addition, the exhalation, or thoracic grunt as practiced also by weightlifters or wrestlers, serves to equalize the pressure increase in the thorax which may result from violent exertion, thus preventing injury to the vital organs. When you yell as a result of tightening your abdominal muscles you are exhaling from the abdomen (diaphragm), expelling the majority of the tidal air (“margin of air” held in your lungs), moreso as with regular breathing, thus increasing the breathing or vital capacity of the lungs. You will then also be forced to breathe in, rather than to hold your breath. Holding your breath can cause a rise in pressure in the chest cavity, which in turn could cause the heart to go into fibrillation. That is, your heart stops beating rhythmically and that could eventually result in the heart stopping. On a spiritual and emotional level, vocalizing such as yelling, yipping, grunting, sighing, promotes release of stress, tension, anger, aggression, etc.

Go to the next chapter: The Cardiovascular System
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