The skeleton of your sex doll is produced from high-quality metal before being covered in thick TPE or Silicone to reinforce it further. The metal skeleton in your love doll is very, very strong, although, because they are produced with metal that has joints and boots, there are parts that are more delicate than the others.
As an example, the human skeleton is created to provide support to organs, tissue, or silicone, strengthening it further. However, some parts of the body tend more to injury, like the hands, ankles, wrists, etc. In direct comparison, metal love doll skeletons are pretty much similar, strong but with some delicate areas.
Furthermore, since a love doll does not have the capacity to inform you that you are stretching a joint too much or applying too much pressure onto a limb, you have to be careful and treat your lobe doll like you would treat a human being.