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Anonymous
When you inhale, pressure increases in your thoracic cavity. When you hold your breath and tighten your trunk muscles, this pressure increases more. Since your thoracic and abdominal cavities are separated by only your diaphragm, abdominal pressure increases too. Thus, pressure is applied to the anterior side of your spine. The spinal vertebrae are eing held in correct posisition by the back musculature, and this correct position is reinforced by a static pressure head transmitted to the anterior side of the spine by the hydrostatic column of the guy, the essentially noncompressible contents of the abdominal cavity. As pressure in the thoracic cavity increases with a big breath held, and this pressure is increased by the itghtening of the abs and obliques, more anterior support develops for the spine. The back muslces support the back from the back; the abs, with the aid of a big breath, support it from the front (figure 58). A weightlifting belt adds to this effect, its main function being to add to anterior support rather than to apply pressure from the back.
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