PubMed · 290621
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R W Bench, C F Gugino, J J Hilgers. 1978. Bioprogressive therapy. Part 9.. https://pubmed.ncbi.nlm.nih.gov/290621/
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The nucleus pulposus of the intervertebral disc exerts a pressure which enables it to support axial compression when contained by the annulus fibrosus. The disc was modelled as a thick-walled cylindrical pressure vessel in which the nucleus was contained radially by the annulus. As a result, the stress in the annulus had radial (compressive) as well as tangential (tensile) components. The radial stress at a given point in the annulus was considered to be balanced by the internal pressure which is expected to arise from the attraction of water by proteoglycans. There was a reasonable agreement between the calculated radial stress distribution and published results on the distribution of water within the annulus. As the internal pressure is expected to be isotropic, the annulus was expected to contribute to the axial resistance to compression of the disc; this contribution would be equal, in magnitude, to the radial stress. Predictions of the pressure distribution within the annulus were similar to published experimental measurements made in the radial and axial directions. The tangential stress within the annulus was considered to arise from the restoring stress in its strained collagen fibrils.
In this and a previous experiment it has been observed that subjects produce innervation patterns (EMG) that are load specific, i.e., they produce concentration patterns for movements made with inertial loads and triphasic patterns for movements made with elastic loads. The protocol of these experiments prevented any adaptive responses to the load changes, therefore, it was assumed that pattern matching to load type was a real time updating response of the peripheral feedback systems. This updating response was assumed to be a mechanism for fine tuning the muscle torque by regulation of the mechanical impedance (stiffness) of the limb. Using a standard equation of motion, it was shown that the velocity is equal to the ratio of the muscle torque to the mechanical impedance. Substitution of this ratio for the ordinate of the scaled phase diagrams was then suggested as a real time updating mechanism to account for the scaled phase invariance recorded in this experiment and in the experiment reported by Ruitenbeek, J.C., Biol. Cybernetics 51 (1984) 11-20.