Low back pain or as in its acronym in English LBP (Low Back Pain), is a picture that makes physiotherapists pull our hairs. No wonder 80% of low back pain is nonspecific; that is, the cause of the clinic is unknown. Very little is known about the biomechanics of the lumbar spine, associated with the pelvic region and movement of the lower limbs and its involvement in lumbar musculoskeletal pain .
This topic is for several entries and is sure to generate a lot of debate, but today I would like to talk about the mechanics of compression when sitting down. Condensation, as surely we all figure, is a set of forces that are generated by gravity (vertical force), the weight of the upper body (head, upper limbs, and head), the powers that create the muscles that are inserted into the body. Lumbar spine such as: iliac psoas, lumbar square, multifid, dorsal width, interspinous, … and muscles that are added away from the lumbar spine, but that have a tremendous specific weight in their biomechanics, in this case I mean to the abdominal muscles: internal oblique, external oblique, transverse of the abdomen and anterior rectus abdominis.
The directions of origin-insertion of each muscle will cause tractions of the lumbar vertebrae. In some cases, this traction will be anterior and caudal (psoas-iliac), posterior and cranial (erectors of the back) or dorsal and caudal (lumbar square). In any case, these forces tend to balance to shape the natural lordosis of the lumbar spine. These compression forces vary in each sitting position, prone position, detestation, walking, … which further complicates their study.
Now suppose we have one or several degenerated discs. Statistically, the L5-S1 level suffers more frequently from discopathy, closely followed by the L4-L5 level, there may be symptoms irradiated to lower limbs or not. Lumbar lordosis is considered a protective curve for the intervertebral disc, so when a patient likes the one in the example walks, stands, or lying down, he will barely experience symptoms, or they will be much smaller than those he usually has in a sitting position.
In sedimentation, local symptoms increase and also those irradiated by a decrease in lumbar lordosis towards kyphosis. Therefore, how we sit down can change the symptomatology significantly (I am generalizing to explain the concept but not always the disc will be responsible for the irradiated symptoms, nor will the lordotic protection curve be the ideal position to reduce the patient’s symptoms ).
Sitting on a chair with a backrest at 90º, the disc pressure is maximum, as the lumbar curve is flattened. If we add lumbar support to this posture, respecting the physiological curvature, the disc pressure decreases and, therefore, the patient’s symptoms as well. A backrest of 110º helps to reduce the disc pressure that decreases even more if we apply for lumbar support in this position.
On the other hand, if the primary support of the back is, for example, in the upper thoracic region, this region is pushed forward, increasing kyphosis in the lumbar region, that is, the lordosis is flattened, aggravating the patient’s clinic.
That is why ergonomics are so outstanding when sitting, a cushion in the lower back is a good option that prevents a bad alignment of the spine. It is unusual for people who work many hours sitting that demands a chair as ergonomic as possible that respects the normal alignment of the spine. Luckily, it seems that awareness has produced its fruits, and a wide variety of furniture concerning our back is currently available on the market. Another useful tip is to take breaks of several minutes every 2 hours, stand up, walk for a while so that the area rests, and thus avoid the deformation of the support fabrics that allows inadequate alignments.