It only takes a moment to see the importance of posture.
Matthew Rampen, B.Sc. of Human Kinetics
A moment, otherwise known as torque, may be defined as the force of an object multiplied by the perpendicular distance from the point of rotation. In our daily lives, moments are created every second; lucky for us; our skeletal frame is supported by hundreds of muscles which counteract the natural moments that are created on our body from gravity. The human spine as a whole (cervical, thoracic, lumbar, sacrum and coccyx) has the highest number of muscle attachments in the human body; a number of them are from vertebrae to vertebrae. Muscles that find both origins and attachments along the spine from the deepest to most superficial are the following:
The most natural posture for the spine contains three curves, and when the spine is in this position it may easily rest its load evenly across intervertebral (IV) discs in between each vertebrae. When an individual finds themselves in a bad posture, for example leaning forward, all of the stabilizer muscles found just along the spine will become actively strained. These are not the only muscles activated, but they are some of the bodies smallest muscles, least used, and therefore can become fatigued quite quickly. As mentioned above, this occurence is due to the muscles counteracting the moment that is being created naturally as a result of gravity. When strained for too long, these stabilizer muscles will fatigue, which ultimately leaves more work (compression and tension in this case) for the IV discs. The IV discs consist of the nucleus pulposus surrounded by the anulus fibrosus. The IV discs can weaken overtime as a result of the stress of a bad posture. Although it may not be troublesome when the load is only the individual’s own head and shoulders (everything above from the specified joint of interest), if the load were to be increased, previously stressed and strained IV discs could result in a number of severe injuries including a herniation of the nucleus pulposus (the protrusion of the nucleus pulposus through the anulus fibrosus). Having a herniated disc can lead to chronic pain resulting from compression of the spinal nerve root by the herniated disc.
Too long of a period of stress on any joint meninges, skeletal muscle or ligament will almost always result in two things: creep and inflammation. Creep is the tendency of a solid object to become deformed permanently under the influence of stress. In other words, it is the result of long-term stress that is below the yield strength of the material (anything above the yield strength would likely cause a tear). When inflammation occurs, the body responds by sending cells to the area called fibroblasts. Fibroblasts create scar tissue in order to repair the damaged areas. To keep it simple, scar tissue is the equivalent to duct tape when it comes to repair: stiff and not very forgiving. On top of all this, creep is facilitated positively by the heat generated from the inflammation. However, it is reported that, with postural aid/adjustment, creep can be prevented by the relief of stress along the joints, muscles and ligaments of the spine (J, Srbely, personal communication, January 30th, 2012).
Moore, K. L., Agur, A. M., & Dalley, A. F. (2011). Essential clinical anatomy (4th ed.). Baltimore, MD: Lippincott Williams & Wilkins.
Slide show: Prevent back pain with good posture - MayoClinic.com. (n.d.). Mayo Clinic. Retrieved April 17, 2013, from http://www.mayoclinic.com/health/back-pain/LB00002_D&slide=2