Strengthen weak muscles and stretch shortened muscles.
Pecs is a shortened version of "pectorals" --the chest muscles above the "abs" (abdominal muscles).
the image looks shortened.
The muscles will atrophy (shrink) if not used.
The food will not be fully break down.
antizamboniism this is the scientific answer
They contract
you excersise
you will die
you exhale (:
contrast
Im not expert, but isn't it the diaphragm and rib muscles, the muscles between the ribs, internal and external intercostals.