Matthew Poole and continuators on Job 33:21

21. His flesh is consumed away , that it cannot be seen , and his bones that were not seen , stick out.

Through pain and pining sickness.

Because there is none left to be seen, but he who before was fat and flourishing is now become a meer Skeleton.

Formerly, because they were covered with flesh and fat. But this Clause is and may be rendred thus, and his Bones are broken and are not seen: which is to be metaphorically understood.