How much muscle wall rigidity is normal?

None: Not quite sure what you mean by muscle wall rigidity, muscles do not have "walls". They are made of bundles of muscle fibers and the bundles are encased in strong elastic tissue called fascia. They have to increase in diameter as they contract, and then relax back to the original shape as they lengthen. A rigid wall would prevent shape changes. Swollen muscles can feel like there's a rigid wall.