How can sustained poor sitting posture lead to pathology/ injury, pain, and ultimately human movement system impairment? While discussing the muscular system is certainly appropriate, look to incorporate the effects of poor sitting on non-contractile structures in your response as well, i.e. joint segments of and around the Lumbo-Pelvic Hip Complex, vertebral segments, spinal discs, ligaments, etc.
The vertebral column that is comprised of 33 bony segments which are classified into 5 regions consisting of the cervical, thoracic, lumbar, sacral and coccygeal segments. Our vertebral column is aligned in a series of curvatures among the 5 regions giving it its “ideal” posture. The cervical and lumbar regions are concave posteriorly (lordosis) which give it it’s “bend back” appearance. The thoracic and socrococcygeal (sacral and coccygeal together) provide a structure called kyphosis, which is convex posteriorly (Neumann, 2010).
Lower Back Pain(postural syndrome) can result from the muscles that support the ribs, sternum, and pelvis being underactive during the sitting position which can reflect in poor muscle tone which requires the muscles that support the verterbral column to provide a mild contraction to maintain upright posture. During long periods of sitting, such as desk work using a computer, the vertebral column can assume a flexed position which decreases the cervical and lumbar lordosis and increases the thoracic kyphosis (Neumann, 2010). Working to decrease impairment syndromes of the lumbar spine requires the muscles of the trunk to be the correct length and strength to minimize reciprocal inhibition and optimal isometric contractions to stabilize the attachments of the limb muscles (Sarhmann, 2002). Looking at the individual length-tension relationship of the muscular system that can contribute to an impairment of the lumbar spine, according to Sarhmann, the abdominal muscles may have a tendency to be recruited more readily than the hip flexors during normal sitting posture. This may be a result of or be created from the hamstrings and gluteus maximus muscles being short or stiff and the back extensor muscles may be long or weak compared to the short and weak abdominals. This muscle imbalance can also create a protracted (forward ) head lean thus increasing the force that normally resists flexion and creating greater pressure on the intervertabral discs (Neumann 2010). Prolonged periods of protraction, may lead to a chronic forward head posture, which can increase the strain on the craniocervical extensor muscles. In addition, this pressure on the intervertebral discs over time, may overstretch and thus weaken the posterior annulus fibrosus which can provide a foundation for pain induced problems as a herniated disk, lumbosacral strain, lumbago, and degenerative disk disease (Sarhmann, 2002).
Looking at an individual who remains sitting throughout most of the day will more than likely create static malalignments around the lumbar pelvic hip complex. The sitting position will ultimately tighten the muscles of the psoas (hip flexor), which will decrease the neural output to the antagonist muscle of the gluteus maximus (hip extensor), which causes the CNS to call upon the synergistic output of the hamstrings to produce the necessary joint force. This altered joint motion creates hypomobility and myofascial adhesions of the hip joint. The static malalignment alters the normal length-tension relationship of the hip joint and leads to synergistic dominance of the hamstrings. Once this joint hypomobility occurs in the hip joint, this person may begin to experience spasms in the activated joints to help minimize the stress at the hip joint (Lippincott, Williams and Wilkins 2012). The resulting factor of this reciprocal inhibition would be lower back pain with possible hamstring spasms during normal daily acitivity. This altered malalignment of the hip joint will also create an altered length-tension relationship of the knee joint that will eventually lead to patellafemoral pain (PFP) and possible Anterior Cruciate Ligament injury.
Helping to prevent or minimize any potential injuries would require this individual to begin a moderate resistance training program to help strengthen the stabilizer muscles, predominantly in the muscles that activate the frontal and transverse planes. Primarily, the muscles of the gluteus medias, tensor fascia latae, adductor complex and quadratus lumborum, oblique complex, in addition to strengthening the erector spinae and rectus abdominus to help maintain posture as well as stabilizing the sacroiliac joint.
Clark, Micheal, and Scott Lucett. NASM Essentials of Corrective Exercise Training. Philadelphia, PA: Lippincott Williams & Wilkins, 2010. Pr
This Corrective Exercise Video below can help you alleviate some of the neuromuscular dysfunctions that are created from sitting at an office desk a good part of the day.