Final answer:
Good posture, with shoulders perpendicular to the floor, aligns the center of gravity with the hips and feet, preventing unnecessary torque and muscle strain. It's essential to avoid back issues that may arise from poor posture.
Step-by-step explanation:
It is important to have the aggressor's shoulders perpendicular to the floor because it relates to maintaining proper posture, which is crucial to avoid back strain and damage to disks. Good posture ensures that a person's center of gravity lies directly above the pivot point in the hips. When a person has good posture, their upper body's weight exerts no torque around the hips since their center of gravity aligns with the hips and feet, requiring minimal muscle action to maintain balance. In contrast, poor posture places the center of gravity in front of the pivot in the hips, causing a clockwise torque that must be counteracted by the muscles in the lower back, leading to larger forces exerted by these muscles and possible back strain or disk damage.