This exercise is to strengthen his core muscles in the belly area, mid and lower back. Core muscles are commonly assumed to begin the majority of full-body functional movement. It determines in large part a person’s posture. Overall, a person’s anatomy is built to take force upon their bones and direct autonomic force through a number of their joints, in the direction they desire. A person’s core muscles align their spine, ribs, and pelvis to resist a particular force — whether that force is static or dynamic.