Position Statement on Back PainYou bend over for an hour of gardening and you can hardly get back up. Then once you're up, it's all you can do to bend back down and pick up your gardening tools.
Most people recover after just an hour in lumbar flexion. But spend the day bent over, and you'll probably have pain and muscle stiffness the next morning. And if you have a job to go back to day after day, you're at risk for back injury and other musculoskeletal disorders (MSDs). Doctors and engineers at the Occupational Medicine Research Center in Louisiana are using cats to understand this problem. This study looks at the effect of constant loads on the ligaments and muscles of the low back.
The scientists used computers and EMG (electromyographic) studies to measure the electrical activity in muscles. The length of the ligament between two vertebral bones was also measured before and after static loading.
The results showed that muscle activity goes down and the ligaments lose tension with a constant load. Under these conditions the spine is unprotected, and injury can occur. The researchers report this happens at more than one level of the spine no matter how much load is used.
Even a short time in lumbar flexion can lead to MSDs. The ligaments stretch or "creep" in response to the load. The larger the load, the greater the creep. The authors report that creep occurs within 20 minutes of bending over. The spine doesn't fully recover even after seven hours of rest. Work activities for farm hands, mechanics, and floor, brick, or carpet layers can cause long-lasting creep in the tissues.
Workers can lose the ability to get back the normal tissue length of ligaments, discs, and joint capsules. Inflammation may occur and become chronic. Based on these results, the authors suggest using anti-inflammatory drugs instead of muscle relaxants for muscle spasm and stiffness after being in one position too long.
Moshe Solomonow, PhD, MD (Hon), et al. Biomechanics and Electromyography of a Common Idiopathic Low Back Disorder. In Spine. June 15, 2003. Vol. 28. No. 12. Pp. 1235-1248.
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