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The torsional rigidity comes from the torso. The lateral rigidity would come from the arms and the legs becoming stiff.
It is defined as ratio of the product of modulus of rigidity and polar moment of inertia to the length of the shaft.
Torsional Rigidity is caluclated as: Torsional Rigidity= C J/l
Rigidity = spiralness + spinginess
In chemistry the rigidity is related to chemical bonds in a molecule.