Final answer:
Intradiscal pressure is indeed higher when seated compared to lying down, as the posture affects spinal load and pressure in the spinal discs, with this pressure being measurable using a water manometer.
Step-by-step explanation:
The claim that intradiscal pressure is up to 11 times greater when seated versus lying down can be seen as true, considering that body posture significantly affects spinal loading and thus the pressure within the spinal discs. When a person is seated, the spine endures a greater load compared to when lying down due to the vertical alignment and gravity. The spinal fluid pressure within the cerebrospinal fluid is generally measured by a water manometer. As indicated in your references, pressure measurements taken with the person sitting up are expected to be considerably greater than when lying down due to the change in the height of fluid relative to the spinal column. Moreover, lifting objects improperly can create immense forces between vertebrae, resulting in high pressures that can damage spinal components. Proper lifting techniques and avoiding extreme physical activities are recommended to manage these pressures.