What happens if your abdominal muscles are weak, how are you able to do diaphragmatic breathing?

Nervous system: Weak abdominal muscles refers to the muscles of the abdominal wall, which are voluntary skeletal muscles. The diaphragm, in contrast, is a separate organ of skeletal muscle controlled by the nervous system and has both voluntary and involuntary innervation - the involuntary innervation is what keeps you breathing all the time even when you're not thinking about it.