Master of Science (MS)
Biological and Agricultural Engineering
More than 30 million people in the United States may have low back pain at any time, and 10 million of them have chronic symptoms. Epidemiological studies indicate that along with axial compressive loads, other factors including repetitive twisting or lateral bending and lifting are significant risk factors for low-back disorders. Literature repeatedly confirms that cyclic occupational functions expose workers to a 10-fold increase in episodes of low back injury and pain. This study examined the biomechanical effects of cyclical loading on the lower back. Twenty in vivo feline preparations were subjected to passive cyclic loading at 20 N (n=6), 40 N (n=7), and 60 N (n=7) for 20 minutes continuously, followed by 7 hours of rest. The skin over the lumbar spine was dissected from the thoracic level to the sacral level and reflected laterally to expose the dorsolumbar fascia. Six pairs of stainless steel fine wire electromyography (EMG) electrodes were inserted into the multifidus muscles of the L-1/2, L-2/3, L-3/4, L-4/5, L-5/6, and L-6/7 on the right side. An "S" shaped stainless steel hook was inserted around the middle of the supraspinous ligament of the L-4/L5 motion segment and connected to the vertical actuator of a Bionic 858 Material Testing System. The load was applied by the MTS actuator with a computer controlled loading system operated in a load control mode; the resulting electrical activity was recorded and analyzed. Results showed that continual cyclical loading on the supraspinous ligament and lumbar spine resulted in creep or laxity within the viscoelastic structures of the spine. The creep then caused desensitization of the mechanoreceptors, located within the ligament. The initial response, due to a decrease in mechanoreceptor sensitivity, was an exponential decrease of electrical activity during the 20-minute loading period for 20N, 40N, and 60N. The greatest percentage of recovery was observed 10 minutes immediately following the loading period for 20N, 40N, and 60N. The electrical activity for all loads increased near the end of recovery. Full recovery of reflexive muscular activity was never observed during any loading period.
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Claude, Lakiesha, "Biomechanical effects of cyclic loading on the lower back" (2003). LSU Master's Theses. 586.