The back is made up of three distinct regions, and two fused bones. The cervical, thoracic and lumbar spine each provide different functions to our daily lives.
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The cervical spine (the neck) allows for multidirectional movement of our heads, turning to look over a shoulder, look up/down, and move our faces towards stimuli.
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The thoracic spine (the midback) is for rotation through our backs, reaching to put on a seatbelt, or turning through the golf swing.
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The lumbar spine is the predominant load bearing region of the spine.
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The Sacrum is the fused bone at the base of the spine which wedges in between the hips.
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The Coccyx is a small bone that is at the base of the sacrum
The cervical, thoracic and lumbar spines are made up of 24 individual joints that form an “S“ shaped curve. The reason for this curve is to allow for mobility of each section of the spine, and at the same time to disperse the load evenly through all of the 24 joints in the back. In between each of these joints are intervertebral discs. These discs absorb forces and load and allow the transmission of these forces through the body. Each disc is named after the joint it sits between. For example, the joints between lumbar vertebrae 4 and 5 are abbreviated to L 4/5.
When you sit, the loads though your L 4/5 and L 5/S 1 lumbar discs are increased by 35% at each joint. This increases the chance of disc pathology if you are sitting for prolonged periods on a prolonged basis, as it stresses the structures that hold the discs in the neutral or “S“ shaped position.
This diagram shows you the angle of load and how sitting posture can affect the angle of loading. Keeping your back straighter when sitting and increasing your core strength reduces the loading of your lower back, and ultimately reduces the load on the disc. Keeping your knees lower than your pelvis reduces the angle of load on the pelvis, and reduces the load through the discs in your lumbar spine.
Postural assessments can be performed by your Physical Therapist, and the area of dysfunction can be addressed via postural correction training or strengthening of your lower back/core, or a combination of both.
As the majority of the population spends more time sitting than they do standing, it is important that when you are sitting you know about the forces that you subject your back to. With a simple correction of posture, you not only reduce the chance of injury, but also create a more therapeutic environment for your body. You can breathe better, reduce stress on individual tissue, and disperse the load, as well as setting yourself up better to type, see what is happening in your surroundings, and perform the activities of your daily work schedule better.
Unfortunately, incorrect sitting posture can lead to not only lower back, but also neck, elbow, wrist, shoulder pain and a myriad of other pain syndromes and dysfunctions, so be sure to spend the time to address your posture. If you have any questions, ask your Physical Therapist, or contact me at Luke@JointVenturesPT.com. Your discs will thank you!
References:
cedars-sinai.edu/.../468325_SPINE_CURVES_OF.jpg
http://www.necksolutions.com/images/sitting.gif