Posture Principles
Filed under: Strength Training
1st Posture Principle Posture is how you balance your body. If you don't balance, you fall down.
2nd Posture Principle The human body is designed to move. It is much easier to walk for 30 minutes than to stand still for 30 minutes. 
3rd Posture Principle Posture, motion & balance depend on the bones, muscles, ligaments, and nerves. Bones support the structure of body. Ligaments hold bones together where they meet at movable joints. Muscles shorten (or contract) in specific patterns to create motion. Nerves control the muscles with messages from the brain.
4th Posture Principle The body learns what you teach it. Pain teaches the body to move differently. If it hurts to move, the body will adapt and move in a way to avoid pain.
5th Posture Principle The body will adapt to posture & motion changes. Over time, the stress of unbalanced posture and motion results in muscle imbalance and joint wear. This begins a vicious cycle of unbalanced motion - causing breakdown - causing more unbalanced motion. Constant muscle and joint stress causes chronic muscle spasm, joint damage (arthritis/DJD) and recurring injuries.
Source: http://www.bodyzone.com/custom/posture_principles.html