One of the first things I do as a Pilates instructor is observe a person’s posture. Good posture is the position of the body that puts the least stress on the muscles, joints, and ligaments when sitting, standing, or lying down. The spinal column is the foundation the body supports itself on. When you look at it from the side, you can see that there are three main curves in it.
The neck (cervical) region and lower back (lumbar) region of the spine have inward curves. The mid-back (thoracic) region has an outward curve. These curves have a normal angle, which is the neutral position of the spine. Maintaining this neutral position puts the least stress on the back and neck.
If you slouch while sitting or standing, you lose the normal inward curve in your lower back. You also increase the curving in the mid-back and neck area. Doing so puts undue stress on the whole spine, because it over-stretches some muscles while tightening others. Also, your head isn’t resting on top of your body then. This forward head position fatigues the neck muscles, leading to increased tension and pain. In good sitting or standing posture the head and upper body are balanced on top of the lower back and pelvis, maintaining the normal curves of the spine. This minimizes the stress on the muscles, ligaments, and spinal discs.
Maintaining good posture requires you to be aware of what good posture is and how it feels. Also, you need the strength and (more importantly) the flexibility to achieve the proper position.