The Back and Abdominal Muscles

Our back muscles are divided into two groups.  Extrinsic and intrinsic.  Within each group, they are arranged symmetrically along either side on the spine in a mirror like fashion with the matching muscle on each side.

Extrinsic and Intrinsic Muscles

The extrinsic group is responsible for upper extremity (arm and hand) and shoulder movement.  The intrinsic group is responsible for any movement of the vertebral column.  They are visible from their

extrinsic muscles of the backV-shape, as you observe their shape from behind in a mirror, as seen in figure 5.1.   They are the: trapezius, latissimus dorsi, levator scapulae and rhomboid muscles.   Other extrinsic muscles are the: serratus posterior inferior and superior.  Their function is to help you to breathe.

Intrinsic muscles (Figure 5.2) are the small and firm muscles that travel along each vertebrae from the pelvis to the cranium.  It is these muscles that can be strained and fatigued and lead to back pain and spasms.  Improper lifting and posture can cause injury in this group.  This group has three layers of muscles.

intrinsic mucles of the backThe first layer consists of the: rotatores, multifidus and the semispinalis muscles.  It is the deep layer that runs along the spine.  This layer is responsible for connecting each vertebrae. They are responsible for your alignment and posture. They keep you upright and work to maintain proper posture.

Throughout the day, as you stand, these muscles are constantly active and firing in effort to help you stay upright.  You normally are not aware of this unless you have a back spasm and the muscles and nerves generate pain.

These deep muscles are short and dense.  They connect and travel from one specific bony origin on the vertebrae to the next vertebrae.  There are several of these on every vertebrae.

It is important that the muscles of each vertebrae is balanced and equal in strength or there will be a misalignment in your spine.  A misalignment can result in over correction and overcompensation from other muscle groups and trigger a back spasm to prevent further serious injury.

Figure 5.1  illustrates the muscle groups involved in back movement and posture.  These muscles are the smallest of the three groups.

The second layer of muscles are larger and shaped like straps.  Instead of joining vertebrae to vertebrae, they join from the vertebrae to other areas of the body.  This includes the head, rib cage and pelvis.  Their purpose is to ensure that your normal posture is correct, stable and that they extend the vertebral column.  These muscles are the erector spinae.

The third and largest layer of back muscles are what join your shoulder blades and joints to your spine.  These muscles are the largest and strongest.  When you are lifting,  these muscles work to keep the trunk stable in order to protect the vertebrae.  The muscles within the second and third groups help to contract to hold the correct curvature of your spine so that it can bear a load safely and balanced. This is done as the larger muscle groups of the rest of the body exert force as in lifting.

Muscle Spasms and Guarding

Back spasms can occur when the deep layer muscles are not firing with the proper timing and duration when called for.  They become fatigued or underused from poor conditioning.   When this happens, the other layers of the back begin to compensate and try to perform the job of the deep layer muscles.

These muscles are not able to perform at the same ability and duration and consequently fatigue.  The deep layer muscles shut down, no longer performing their primary function.   The outer layer muscles then fatigue and can progress into strained or sprained muscles.

When muscles no longer function to protect the vertebrae correctly, other surrounding muscles try to protect the column by becoming very rigid so as to limit movement to avoid any risk of injury to the discs and nerves.

This occurs during a back spasm as the outer layers of the back freeze in order to protect the deeper ones and consequently the spine.  This phenomenon is known as “guarding”.   It is very unpleasant and painful when it occurs on larger muscles and most people are likely to resort to pain medication and muscle relaxants.

When a muscle or group of muscles guard a specific area such as a joint or disc space, sometimes the area is no longer stable as the guarding locks the joint into a new position.   Here the muscles that were protected from the outer layer have fixed in to a new position or misalignment. There is an imbalance of strength and length in the muscle that remains as the pain subsides.

This presents a risk to the area, disc or nerve and perpetuates an additional problem in a cycle of pain and injury.  Most people cannot sense that they are out of alignment and continue to perform their daily activities.  They assume that they are healed and risk re-injury and further guarding that may exacerbate further misalignment and pain.

Your Abdominal Muscles

The abdominal muscles (Figure 5.3) such as the Rectus abdominus (six pack) help to balance out the constant flexing that the back muscles perform.  They abdominal musclesserve to contract and draw the upper body down toward the hips.  The contraction of the abdominals produce a pressurized cavity that helps to relieve any weight that is put on the spine.  This serves to protect the discs during a lift or with posture.

It is important that these muscles are active during times of lifting because they keep the normal curvature and help to prevent disc injury.  Those with weak or unconditioned abdominals are prone to back injury because of this imbalance.

Other vital abdominal muscles include: the internal and external obliques and the transverse abdominus.  The transverse abdominus is the ‘corset’ of thin muscle that surrounds and contains the abdominal cavity.  The action of this muscle helps to provide sustained upward force to relieve pressure on the spine.

This muscle is needed during everyday daily tasks where lifting is required.   Very weak and unresponsive abdominal muscles lead to excessive anterior pelvic tilt and risk injury to the lumbar spine and disc, causing pain.

The Low Back Pain Program eBook provides comprehensive, step by step, lower back exercises that help to properly condition and strengthen the back and abdominal muscles.   This allows them to provide the required protection for the lumbar spine and pelvis against disc injury and lower back pain.  Other muscle groups such as the hip flexors and hamstrings are also targeted in the eBook to address their affect on lower back pain.