Why does sitting for long periods of time increase back pain sometimes? This question has been studied for the past 50 years and researchers still find controversy when trying to answer the question. At the heart of the dilemma is a mechanical dynamic between body weight, body posture, and spinal disc load.
A loading, compressive force on a spinal disc creates a certain amount of pressure within the disc which is like a marshmallow in between two graham crackers being squished together. This pressure can be measured with special devices inserted into the disc. With various body positions like lying down, sitting, standing and bending forward, the pressure amounts vary and were first reported in the landmark study performed by Dr. Nachemson in 1981. In this study, he found that sitting produced higher pressures in the spinal disc than standing. So, for the past thirty years, clinicians have told patients with degenerative disc related back pain to avoid prolong sitting because high pressures lead to more disc pain. However, in an attempt to validate Dr. Nachemson's original finding, another Dr. Rohlmann found that standing produced higher disc pressures than sitting.
Are Dr. Nachemson's long-standing conclusions incorrect? As it turns out, the contradictory results are most likely related to posture. The sitting posture was different between the two conflicting studies and thus produced different results. Amidst this scientific controversy lie some practical solutions for millions of people who suffer from back pain while sitting.
The first solution for back pain while seated has to do with the position of the arms. A recent study concluded that sitting with the arms supported can reduce disc pressure by upwards of 40%. With less pressure on the discs, pain in the low back should reduce as well. The reason why arms supported on the thighs or arm rests relieves back pain is because the load of the upper body is transferred through the arms instead on through the spine. If the arms are dangling, then all that weight compresses and hangs on the spine. Putting both arms down onto a supported surface creates a stable three-legged "stool" where all the "legs", two arms and the spine, are sharing the load equally. Try it for yourself. Arms dangling versus arms supported while in a seated position. Feel the difference that an increased base of support can do for an aching back.
Another way to relieve back pain while seated is to use the backrest on the chair. With all the tasks in front of the chest, the tendency is to sit on the edge of a chair without using the back rest. Unless you have stellar core strength, you will not be able to sit with the back unsupported for very long without causing pain. Besides, resting the spine against a chair back helps to eliminate a slouched posture. Slouching shifts the center of gravity right over the front of the spine and compresses the discs. By sitting up against a backrest, the center of gravity shifts away from the spinal disc and the disc pressure is relieved.