The spine has three natural curvatures, which can become exaggerated in one direction or the other. Optimal (or neutral) posture is shown on the left, with exaggerated postures to the right.
Optimal Posture. In optimal posture, a vertical line passes through the midline of the knee, the lumbar vertebrae, the shoulder joint, the cervical vertebrae and the earlobe.
Kypholordotic Posture. An increased thoracic and lordotic curvature is observable. The head is held slightly forward, often becoming the most anterior segment of the body. The pelvis tends to tilt anteriorly with an increase in lumbar lordosis (inward curve).
Swayback Posture. The pelvis is gradually becoming the most anterior segment of the body, and there is an increase in lumbar lordosis. The knee joints tend to be hyperextended. Abdominal obesity worsens this posture.
Flat-Back Posture. The pelvis has a posterior tilt with very little normal inward curvature of the lumbar spine. The knee joints are often hyperextended. The head is sometimes tilted slightly forward. The thoracic spine may be flexed forward a bit.
Adapted from IDEA