Healthy posture is based on natural positions that balance and support your skeletal system's curves and weight-bearing abilities against the force of gravity. The idea that standing straight and tall is best for your back posture is a misconception. Ideally, you should stand with knees slightly bent and shoulders slightly back. This position works with the pelvis and lumbar, thoracic and cervical curves of your spine to achieve a vertical equilibrium. Habitually poor posture contributes to back pain and may indicate a bone deformity or another underlying medical condition.
The American Physical Therapy Association (APTA) delineates good standing posture as alignment of the ear, shoulder, hip, knee and ankle, as seen from the side. When sitting, your head should be erect, and back posture should maintain the three natural spinal curves. In sleep, pillows and mattresses are used to maintain spinal curves and support the head and neck so they are level with the upper back.
Kyphosis, or hunchback, is an unbalanced posture that can cause neck and back pain. The head is pushed forward, in front of your gravitational center. The upper back is rounded, accentuating the thoracic curve. According to the Maryland Spine Center (MSC), this condition can develop from unhealthy posture habits, bone and joint degeneration and spinal deformity. Severe cases diagnosed as Scheuermann's kyphosis create a noticeable hump in the upper back.
Lordosis is a back posture that exaggerates the lumbar curve into a position often termed swayback. Standing with locked knees contributes to this unhealthy posture that aligns the head behind your center of gravity. Shoulders may also be pulled back too tightly. The MSC reports behavioral and developmental causes for this condition that may create neck or back pain.
Scoliotic curvature is an abnormal sideways curve of the spine that results in improper alignment of the spine, shoulders and neck. Visible symptoms may include uneven shoulder height or a nonvertical neck angle. The American Chiropractic Association notes that scoliosis may cause back pain or progressively impinge on internal organ function. The majority of scoliosis cases are mild (less than 20-degree curve), however, and don't pose serious threats to healthy posture.
Other Abnormal Postures
Unhealthy, rigid back postures associated with head injuries are more extreme and require immediate medical attention. Decorticate posture is a body position in which the arms and hands are curled inward, and the legs are held straight outward. Decerebrate posture leaves arms and legs extended, toes pointed downward and head pushed backward. The MSC relates that these may indicate a brain tumor or stroke.