Bending with Back Pain - Not at the Waist!
It is commonly understood that when bending over to pick up an object, it is mechanically more efficient to bend the knees and to do the lifting with the larger and stronger leg muscles than to keep the knees straight and to lift with the smaller lower back muscles.
In yoga class, many practices involve bending over with straight knees to stretch the hamstrings. Stretching the hamstrings is excellent for lower back health, but with knees straight, the room for error is narrow, and many students mistakenly bend at the waist (figure B) rather than the pelvis (figure C) putting their lower back at risk.
Bending at the waist (B) puts enormous stress on the intervertebral discs of the lumbar spine that can lead to their bulging or herniation. This image above demonstrates the bio-mechanics of forward-bending with knees straight.
In forward bending, the whole pelvis pivots from a vertical to a horizontal position over the femur heads, and the tailbone lifts upward opposite the spine's descent as seen in figure C where the woman's pelvis tilts forward at a 90° angle in relation to her femurs. The ability to tilt the pelvis this far is enabled by long hamstrings which run from the hip to the lower leg (as indicated by the straight black line behind her femurs).
With short hamstrings, as in figure B, the pelvis is restricted from tilting to a 90° angle. To bend further, the woman has to excessively flex her lumbar vertebrae putting herself at greater risk for disc bulging and herniation.
This is precisely what happens when someone bends at the waist even if their pelvis is perfectly capable of pivoting over the femur heads. We often hear instructors say, "Place the hands on the hips and bend forward." But place the hands where on the hips? There is a great distance between the top and bottom of the hips. Many people mistakenly place their hands at the very top of the hips with the index fingers and thumbs resting on the rim of the pelvis. This hand placement has the psychological effect of cutting off any movement below the hands while folding in half at the lumbar region at the top of the hips. Their tailbone remains fixed, pointing downward (see the difference between the tailbones in figures B & C). This puts their lumbar discs under tremendous stress.
However, if the hands are placed at the bottom of the hips where the pant pockets and femur heads are, this allows the pelvis to tilt forward and tailbone to start to move upward.
In yoga, some schools consider Figure A a correct forward bend where the stretch is distributed equally between the hamstrings and lower back muscles with both hip and spinal flexion whereas other schools consider Figure C a correct forward bend where the hamstrings take all the stretch with hip flexion and the lower back none, i.e. no spinal flexion. Certainly for people with back problems, Figure C would provide the least amount of strain. Figure A allows for a moderate lengthening in both the lumbar and hamstring regions whereas Figure C shows a more cautious bend to avoid excessively flexing the lumbar spine.
For those who suffer occasional or chronic lower back pain, I suggest eliminating forward bending completely from both standing and sitting positions due to likely compression in the lower back. In my lower back yoga class, we gently lengthen out the hamstrings while lying on the floor in a supine position to avoid even the slightest stress to the lumbar spine.
Tight hamstrings restrict the pelvis from tilting further forward. Bending the knees provides slack to the hamstrings thereby allowing the pelvis to continue tilting. With knees bent, the leg muscles bear the brunt of lifting a heavy load rather than the much smaller lower back muscles. For further lower back support, drawing in the abdominal muscles assists in proper lifting, much like a delivery person who wears an abdominal belt. Drawing in the abdominals is especially important when the object is off to the side, like when lifting luggage, which involves lateral spinal flexion.
In cases of serious back pain, bending at the bathroom sink to brush one's teeth can be problematic. This requires bending the knees as best one can (open the cabinets underneath the sink if possible) and pulling in those abdominals!
Take a class
I have applied these principles in my lower back yoga class with twenty-eight practices to alleviate compression of the lumbar discs. If you'd like to try it, it is available as an iphone app.
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