Postural Biomechanical Stability and Gross Muscular Architecture in the Spine

Consider a ligamentous thoracolumbar spine specimen, sacrum-T1, fixed at the sacrum and carrying a load at T1. It has been determined experimentally that such a spine buckles when the load reaches a critical value of about 20 N (Lucas and Bresler, 1961). Or consider a lumbar spine specimen, sacrum-T1, its critical load is less than 90 N (Crisco, 1989; Crisco, et al., 1990). On the other hand, we have a world-class weight lifter who can carry more than 3000 N without damaging the spine (Granhed et al., 1987). Simply stated, the difference between the two behaviors is the spinal muscles. The same is true in another example. Compare a healthy normal person and a polio patient. The latter, with the back muscles paralyzed, cannot even hold his/her own trunk in the upright position. The important role of the muscles as the stabilizers of the spine is unquestioned and essential for its function. A deficiency in either muscle function or bony-ligamentous function will eventually lead to disabling clinical problems.

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