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Chiropractic Research Review

Effect of Postural Changes and Carried Load on the Lumbar Spine During Forward Bending

Frequent heavy lifting motions with weight bearing appear to increase the risk of low back pain. Exactly how much load, and in which positions the risks for low back problems are imminent, remains unknown.

The best method of producing direct recordings of the load on the spine is accomplished via in vivo intradiscal pressure measurement. To obtain a more profound understanding of changes in disc pressure, it is necessary to examine other factors that affect the load of the lumbar spine, and to compare the relationship between theoretical loads and actual loads on the lumbar spine with and without external weights.

In this study, researchers measured intradiscal pressure, action potentials of the trunk muscles, and changes in trunk motion of three healthy males between the ages of 24 and 26, all without any history of lumbar or lower extremity pain. Subjects performed a series of motions: from upright standing slowly bending the trunk forward with extended knees, maintaining the maximum forward bending position for 1-2 seconds, then rising the trunk to the standing upright position. Measurements were performed with and without the subjects carrying a 5-kilogram weight on each arm. Recorded values were then compared with theoretical values for analysis, based on the principle of levers.

Results: The load of the lumbar spine and electromyographic activities of the back muscles increased in proportion to the tilting angle of the trunk both with and without the use of external weights. However, use of external weights created no significant activity in the abdominal muscles. The actual measurement values on the lumbar spine were "a bit larger" than the theoretical values at every tilting angle measured, which indicated that the actual values "were larger than expected."

Conclusion: "These findings suggest that heavier loads than up till now believed are facing the lumbar spine even during everyday motions, such as 'just bending the trunk forward.' Consequently, injuries or hernias of the intervertebral disc in the lumbosacral spine may be considered to be induced by simple everyday motions of the trunk while bending forward."

Takahashi I, Kikuchi I, Sato K, et al. Mechanical load of the lumbar spine during forward bending motion of the trunk - a biomechanical study. Spine Jan. 1, 2006;31(1):18-23.

Chiropractic Research Review

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