The wealth of technology and automation has begun to take a toll on public health. People are less active and are no longer spending as much of their free time engaged in physical activity. This new environment is producing more inactive, less healthy and non-functional people who are more prone to injury. This continual decrease in everyday activity has contributed to many of the postural deficiencies seen in people.
Posture is dynamic. Functionally, our bodies are reacting to and working against gravity and other stresses to maintain balance. Good sitting posture maintains the three normal curvatures of the spine. The lumbar (lower back), thoracic (mid-back), and cervical (neck) transform the spine into a flexible unit allowing the body and head to be erect with minimal muscular effort(1). The long term effects of poor sitting posture have been associated with numerous painful conditions relating to the function of muscles, joints, ligaments, nerves, connective tissue, circulation, respiration, and digestion. Common associated diagnosed conditions include temporomandibular joint dysfunction(TMJ), headaches, neck pain, shoulder pain, repetitive strain injuries, mid and low back pain, thoracic outlet syndrome, and myofascial pain syndrome(2 ). More importantly, poor sitting posture may adversely affect activities of daily living and overall energy level at work and home.
The idea of good posture is of increasingly great importance in maintaining well-being and optimal health, especially during a time when our society has shown trends of increased time spent watching television, sitting in front of computers due to occupational duties, working sedentary desk jobs and commuting long hours. Over a prolonged period of time the muscles of the lumbar spine, thoracic spine & cervical spine become adapted to this awkward position and develop alteration in static length-tension tissue relations(2 ).
Consideration must also be given to the effects of muscle and ligament tension on disc pressure. An increase in disc pressure in poor sitting posture is caused by alterations in the center of gravity, load distribution and ligament tension.
When sitting in poor posture for prolonged periods without movement there is a sustained compression resulting in fluid loss from the disc. As the disc becomes severely dehydrated, nutrition is compromised and the process of disc degeneration is accelerated. There is a loss of shock absorbing capacity with increased risk of injury to the disc and other spinal structures. There is a loss of disc height which increases the potential for a pinched nerve.
The amount of pressure in the disc is affected by the manner in which one sits, with the body either flexed forward or upright. There is 40% more disc pressure in a poor sitting posture (unsupported – slumped) compared with standing. There is an increase of 85% in disc pressure when leaning forward in a poor sitting posture. Therefore, when the lower back is compressed, there is a greater increase in disc pressure in poor sitting posture compared with positions which maintain the lower back (lumbar spine) in the neutral or normal back posture. This stresses the importance of movement while sitting to avoid these damaging effects of prolonged static sitting and posture related pain.
Poor sitting posture affects the cervical region and is known as forward head posture.
Forward head posture is formed by the flattening of the lower cervical spine (C3-C7) and the skull is in a position of extension. It is characterized by increased flexion of the lower cervical and upper thoracic regions, increased extension of the occiput on the first cervical vertebra and increased extension of the upper cervical vertebrae(4) .There may also be temporomandibular ( TMJ) joint dysfunction with retrusion of the mandible. This altered structural position can cause changes in the length tension relationship of the muscles of the spine. Muscles that are usually tight are the upper trapezium ,levator scapulae, the deep cervical neck flexors ,suboccipitals and the scalene muscles. These alterations of the muscles can cause headaches due to impingement on occipital nerves from tight or tense upper trap muscles, decrease in local muscle function of spinal stability resulting in cervical and lumber disk derangements (including intervertebral disc posterior directed bulge and herniations) due to narrowing of the intervertebral foramina in the upper cervical region, which may impinge on the blood vessels and nerve roots , irritation of facet joints in the upper cervical region, and impingment on the cervical plexus from levator scap muscle tightness(4). Muscles that are stretched and weakened include the lower cervical and upper thoracic erector spinae. This can cause lower cervical disk lesions from faulty flexed posture.
Poor sitting posture can also affect the thoracic region and is known as round back or increased kyphosis characterized by an increased thoracic curve and protracted scapulae which causes rounded shoulders. This causes tightness of the pectorals(major and minor) , latissimus dorsi ,serratus anterior, levator scapulae and upper trapezius muscles. Muscles that are stretched and weakened include the thoracic erector spinae and scapular retractor muscles( rhomboids and upper /lower trapezius) .Due to the tightness in pectoral muscles the position of the shoulders becomes adapted into the position of internal rotation because the humerus in the glenoid fossa of the shoulder is deviated from its normal resting position. This altered position(shoulder impingement) can cause the humerus to be out of static alignment and can cause decreased space for tendons such as the supraspinatus muscle of the rotator cuff to operate efficiently. This decreased space can cause functional disorders such as shoulder bursitis and rotator cuff impingement upon shoulder movements such as shoulder flexion and abduction.
Poor sitting posture affects the lumbar spine and this results in an increased lumbar lordosis . This causes an increased anterior tilting of the pelvis and causes low back rounding. . When the lower back is flattened from poor sitting posture, loading on the front part of the disc is increased by the weight of the body acting downwards causing the disc to become deformed which stretches the back part of the disc, increasing the tensile force and high stress peaks. The resultant tensioning caused by sitting and forward bending dramatically increases the ligament force and is a source of potential damage to the ligaments and the disc of the lower back. Subsequently, the hamstring complex, adductor mangus, rectus abdominus and external obliques become overactive(tight,shortened) and the gluteus maximus, erector spinae, intrinsic core stabilizers, hip flexor complex and latissimus dorsi become underactive( weak, stretched). During prolonged slump sitting, the deep back muscles such as the multifidus and internal oblique will atrophy and lose their cross-sectional area causing weakening of the back and dysfunction of facet joints.The multifidus is one of the only muscles to provide direct stabilization to the lumbo-sacral joint (L5-S1) which is often involved with degenerative changes(1). The damage is associated with loss of multifidus reflexivity and hyperexcitablity, acute inflammation in the ligaments, fascia, discs and capsules of the joints behind the discs often involved in facet joint syndrome(1). As a result, the superficial muscles of the back become tight and reduce spinal stability.
The gluteus maximus and latissimus dorsi along with the thoracolumbar fascia work synergistically to form the Posterior Oblique Subsystem. As a compensatory mechanism for the under-activity and inability of the gluteus maximus to maintain an upright trunk position, the latissimus dorsi may become synergistically dominant (overactive or tight) to provide stability through the trunk , core and pelvis. Because the lats crosses the inferior angle of the scapulae and inserts onto the humerus it can alter the rotation of the scapula and rotation of the humeral head within the glenoid fossa. Over-activity or tightness of the lats can affect the shoulder and upper extremities leading to a variety of shoulder and upper extremity injuries.
The Anterior Oblique Subsystem is similar to the POS in that it also functions in a transverse plane mostly in the anterior portion of the body. The prime contributers are the internal and external oblique muscles, the adductor complex and hip external rotators. The obliques as well as the adductor complex produce rotational and flexion movements and also in stabilization of the lumbo-pelvic –hip complex. Because of increased spinal flexion due to poor sitting posture and the situation of an anterior pelvic tilt the length tension relationship causes lumbar lordosis to be increased
and this causes increased stress in the hamstring complex and adductor mangus which is compensating for a weakened gluteus maximus and erector spinae complex to stabilize the LPHC and thus resulting in groin strains and low back pain.
The Lateral Subsystem is composed of the gluteus medius, tensor fascia latae, adductor complex and the quadratus lumborum. Due to compensation for weak gluteus maximus from poor sitting posture, these muscles will shorten and compress, as a result creating tension and discomfort.
The Deep Longitudinal Subsystem is composed of the erector spinae, thoracolumbar fascia, sacrotuberous ligament, biceps femoris and peroneus longus. The primary function is force transmission longitudinally from ground to trunk.. This system is key for stabilizing not only the lumbo-pelvic-hip complex but also the trunk. Because of anterior tilting of the pelvis due to poor sitting posture, the erector spinae is working at a submaximal level and this causes the biceps femoris to become overactive to maintain stability of the LPHC. This will alter the position of the pelvis and sacrum and affect the sacroiliac and iliofemoral joints. Dysfunction in any of these structures can lead to SIJ instability and low back pain(LBP).
Treatment of postural dysfunctions may involve regaining the normal length of shortened muscles, mobilizing stiff extremity and spinal joints, strength and endurance training of postural muscles, addressing environmental/ergonomic factors, and education of postural awareness and correction. Awareness is the key to the success of postural re-education. Just like your body has adapted to poor posture over a number of years, you can allow your body to adapt once again to its natural structural state.
The human body simultaneously coordinates these subsystems during activity. Each subsystem individually and collectively contributes to the production of efficient movement by accelerating, decelerating, and dynamically stabilizing the HMS during motion(3).
REFERENCES
1 Neumann, Donald A. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. St. Louis, MO: Mosby/Elsevier, 2010.
2 .Falla, Deborah, Gwendolen Jull, and Trevor Russell. “Effect of Neck Exercise on Sitting Posture in Patients With Chronic Neck Pain.” Journal of the American Physical Therapy Association (2012): n. pag. Print.
3. Clark, M.A. & Lucett, S.C. (2011). NASM Essentials of Corrective Exercise Training. Lippincott, Williams & Wilkens. Baltimore, MD, 8-81.
4. Kisner,C, Colby,LA. Therapeutic Exercise: Foundations & Techniques. Phila,PaFA Davis&Co. 1992.