Sitting. It's Hurting Your Back! Part I

Do you, like millions of other Americans, sit for extended periods of time throughout the day?  Do you work at a desk?  In front of a computer?  Drive or travel a lot for work?  If so, your occupation is weakening your back and predisposing you to a back injury and future low back pain.

Low back pain is an extremely common condition that afflicts millions of Americans.  There are numerous causes of low back pain and the condition is relatively complicated and generally not well understood.  However, one aspect of low back pain that research has recently shed light on is the negative effects of long term sitting. 

Extended sitting in all positions is relatively bad for the lumbar spine or lower back.  Sitting upright, of course, is better than slouching but it still has many of the same negative effects as slouching.  Biomechanical research on the spine shows that sitting is a flexion activity (like bending over).  Imagine what your low back would feel like if you spent long periods of time bent over.  The main difference between sitting and bending over is how gravity affects the spine.  While sitting, gravity acts to compress the spine and load the disc.   While bending, it acts to further flex the spine, pulling your body towards the ground placing even more stress and pressure on the ligaments.  Both positions are far from ideal.

How can sitting be so comfortable, yet so bad for our backs?  When we sit, and our spine begins to flex, our low back muscles called erector spinae muscles (the ones that provide 80% of our lumbar support) get stretched out.  As a muscle stretches, it loses its maximum strength, or power, so our erector spinae muscles get weaker as we sit and eventually turn off and stop providing support.  This has a twofold effect on our spine; one effect is that a muscle that shuts off for extended periods of time loses strength and stamina and essentially atrophies (shrinks) over time and gets weaker.  The second effect of these muscles shutting off is that the weight of your body is now resting on your ligaments and discs or static stabilizers.  This has the negative effect of causing these ligament s and structures to stretch over time and become lax.  This means that the support systems of your low back (the muscles and ligaments) are providing very little support to your spine leaving it weakened and vulnerable.  

The effect of the ligament laxity and stretching lasts long after you get up from sitting.  In fact, studies suggest that it may take a full 24 hours for your ligaments to shrink back and again provide proper support.  This essentially leaves the spine vulnerable to injury without proper support.  In practical terms, it is best to avoid any repetitive bending or heavy lifting after extended sitting.   I would suggest that after a long day of sitting you should be especially careful how you lift and bend and actively prepare your spine (by tightening your abdominal muscles) for any lifting or deep bending (reaching to the floor) no matter how  light the object might be.  This would be most important the first hour after sitting.

We may be comfortable sitting because we are not actively using our muscles, instead resting on ligament support, so our muscles don’t get fatigued or tired or over worked.  However, we very often feel the stiffness, discomfort or pain after sitting as we transition to standing.  This is a direct result of the loss of support of the spine and temporary instability in the spine that the long term sitting has created. 

The weakening and deconditioning of the lumbar erector spinae muscles or stabilizers has a long term effect of weakening your spine over time.  The erector spinae muscles are your primary, and most important lumbar support muscles.  As they weaken, it can lead to chronic low back instability, poor biomechanics, and ultimately low back pain.  It can also predispose the spine to acute injury. 

Follow my next post to learn how to counter the negative effects of long term sitting in Part II of this series.