It is of extreme difficulty to generlaize hypotheses for spine stability, even in normal population. This field is vast and cannot simplified or framed in this way.

Thank you very much for your answer.

You might consider looking up "induced Acceleration Analysis" a method for assessing the effect of accelerations on one segment across other linked segments in a MS model.

There are several studies reporting pressures inside the intervertebral discs during various activities. Have you reviewed those papers? There are papers reporting finite element model results.

Thank you John for your answer . Yes, I have. most of FE models did not look at the whole spine and did not consider the effect of hand, leg or head on the spine.

Thanks Christopher. for what kind of subject these figures represent thorax and hip angle? Are these for one subject or more than one? fore healthy subject or for patient? female or male?

when loading of a segment in spine changed muscle activity also change . surface EMG or even better needle EMG ( recruitment count) can help us in this part

I believe that best way is define a mathematical model. Using Anthropocentric and motion capture data  and some known mathematical arguments, you can do this. other ways like models and general computer programs like MAT-LAB and Maple and so on may be useful.