So it is with our lumbar spine. When we flex it bending over, it feels pretty effortless to us, but the pressure being exerted is tremendous. It has been estimated that even utilizing proper lifting squat form, maintaining a neutral spine, lifting just 59 lbs. can create a compressive force in the lumbar spine of over 1568 lbs. (McGill, 82). And that’s with the all the active elements (musculature) of the back all firing to help support the load. When we flex the lumbar spine past a certain point, many of the major supporting muscles stop actively helping to support the load and the load is then almost entirely supported by only the passive elements (ligaments, vertebral discs, connective tissue in muscle). That’s a lot of pressure on Pinocchio’s strings! You can see why I am always instructing you on maintaining a neutral spine when lifting.
Know thyself!
It is important for everyone to maintain a healthy low back, but especially so as we age. Although all the structures of the low back are challenged with age (sarcopenia, osteopenia, osteoporosis, etc.) and use, this piece will focus on the intervertebral disc because it is especially vulnerable.
(Illustrations redrawn from McGill, 44 and 40)
The disc is placed between each vertebra to allow mobility and provide shock absorption for the spine. It’s built something like a jelly doughnut (more like a jelly bagel!) with a soft gelatinous middle (nucleus pulposus) and tough, though pliable, concentric, laminated bands of fibrous material (anulus fibrosus) that surround and contain the nucleus pulposus. Looking at the illustration above, one can see that these outer rings are configured much like plywood and depend on the coherence of the layers for its overall strength. The “flat” surfaces of each vertebra between which the disc is sandwiched (end plates) are pliable, somewhat like a drumhead, and provide some give each time the disc is compressed. Because the material within the bony body of the vertebrae is a matrix of spongy bone (trabecular bone), it provides “the give” allowing the plates to bend. The discs are also supported by ligaments that run in front of them along the spine (anterior longitudinal ligament) and behind them (posterior longitudinal ligament) and then the spine is stabilized by a network of active elements (muscles) and passive elements (ligaments, fasciae).
Over time, uneven application of pressure (flexion of the lumbar spine is the biggest culprit here) on the laminated, concentric laminated bands can cause the bands to separate and crack. Furthermore, as we age, the mass of spongy bone within our vertebrae can decrease, providing too much give in the end plates, causing them to split and leaking the gelatinous material into the body of the vertebrae. This in turn decreases the shock absorption ability of the disc, increasing the pressure and separation/cracking of the fibrous bands, causing them to bulge (protrude) out. If the cracking gets bad enough the inner gelatinous material can squirt out (effuse) of the disc. Either protrusion of the fibrous band or effusion of the gelatinous material can cause severe pain.
What you can do!
Before we all despair over our doomed low backs, know that there is hope. The collapse described is more of a function of overuse, improper use, than age. Much of this can be avoided. If fact, proper exercise can strengthen some of the structures involved. Since flexion of the lumbar spine is the main culprit in injury for most of us, one way to look at this is that we only have so many lumbar flexions we can do in one life time before our discs break down. We want to use them wisely, on only the good stuff (use your imagination!). A worthy goal is to have one lumbar flexion left just before you die – not a bad way to go out!
So here are some helpful hints so save your low back until the end.
1. Use proper lifting techniques. Some links are provided below for basic instruction.
www.mayoclinic.com/health/back-pain/LB00004_D
www.bnl.gov/esh/shsd/pdf/safe lifting and carrying techniques.pdf
2. Try to maintain proper alignment when sitting, but get up as often as possible and shift sitting positions. Sitting for long periods of time, even in proper alignment, loads the low back without almost any aid from core musculature, and the total lack of movement decreases circulation to the vertebral bodies themselves.
3. Walk briskly. Sauntering (mall walking) and standing loads the low back without much support from the core muscles. Walking briskly, swinging the arms from the shoulders (not just from the elbows!), engages the core muscles and shifts mass distribution to support the low back. This can be very therapeutic for back pain.
4. Don’t do movements that require flexion of the spine as soon as you wake up in the morning. You are taller in the morning then when you go to bed – perhaps as much as 19mm! This is because the intervertebral discs hydrate at night, swelling the discs. This can increase the disc bending stresses by 300% and the ligament stresses by 80%. 54% of this increase is lost within the first half hour after rising from bed (McGill, 96). So take your time and enjoy your coffee in the morning before dashing about to work, the gym, or yoga.
5. Don’t go right from activities that cause you to flex your spine for long periods of time (sitting in a car, sitting on a couch, sitting at your desk for hours, bent over gardening, sitting on the bus for hours before and after athletic competition, etc) to lifting loads. The soft tissue that support the spine have special nature to them (a thixotropic quality) that allows them to “creep” to a new length and hold that length when under pressure for extended time periods. The ligaments that limit how much the vertebrae can move will become longer and stay that length for a period time after sitting (see figure below). This takes away much of the passive support of the spine, risking injury when lifting.
(Illustration redrawn from McGill, 63)
6. Maintain strong core musculature. There are lots of rumors and old disproved theories on why a strong core helps support the spine, so see me for the real story some time. The bottom line is that a strong core is crucial to spinal health. Sit ups, crunches, curl ups, hang curls can put tremendous pressure on the low back. But the rectus abdominis and core muscles of the trunk can be strengthened without these exercises. Investing in a good trainer to help you is the best way to go with this. For a choice of independent personal trainers, check out the websites below and feel free to ask my advice when matching your needs to a particular trainer.
Somerville
The Training Room, www.thetrainingroomboston.com
Cambridge
Durbrow Performance, www.durbrowperformance.com
Back Bay
Balans, www.bostonbalans.com
Kenmore Square
Joint Ventures Physical therapy and Fitness, www.jointventurespt.com
There is much, much more to back pain than failure of intervertebral disc integrity. For more information about how different exercises affect the low back and advice on which exercises might be best for you, please schedule an appointment with me. My office hours can be found at www.soarbody.com.
References:
McGill, Stuart, Ph.D. “Low Back Disorders: Evidence-Based Prevention and Rehabilitation, 2nd Edition.” Ed. Robinson, Loarn Champaign, IL, Human Kinetics, 2007
Other references utilized:
Clemente, Carmine D. “Anatomy, A regional Atlas of the Human Body, 5th Edition”
Baltimore, MD, Lippincott Williams & Wilkins, 2007
www.mayoclinic.com
www.bnl.gov
