What is the connection of sighing, to his bones clinging to his flesh?
Radak: Sighing and affliction of the heart weakens the flesh. When there is screaming with it, all the more so the flesh totally weakens until the bone sticks to the skin - "Tzafad Oram Al Atzmam Yavesh Hayah cha'Etz" (Eichah 4:8). The skin is called Basar, for man's skin is flesh; it cannot be peeled from a man like an animal's skin. Also Basar is called skin - "Yochal Badei Oro" (Iyov 18:13).
Malbim: The flesh of the intestines sticks to the bones due to the sound of the sighing. This annuls the power of digestion - "b'Ori uvi'Vsari Davkah Atzmi va'Esmaletah b'Or Shinai" (Iyov 19:20). This describes the standing of the nation at a time of pursuit of (attempt to undermine) the faith.
