|Classification and external resources|
Different regions (curvatures) of the vertebral column
A neutral spine or good posture refers to the "three natural curves [that] are present in a healthy spine." From the anterior/posterior view the 33 vertebrae in the spinal column should appear completely vertical. From the sagittal view, the cervical region of the spine (C1-C7) is convex anteriorly, the thoracic region (T1-T12) is convex posteriorly, and the lumbar region (L1-L5) is convex anteriorly. The sacrum (S1-S5 fused) and coccyx (on average 4 fused) rest between the pelvic bones. A neutral pelvis indicates the anterior superior iliac spines and pubic symphysis fall in the same vertical line.
Posture and natural curvatures
The word posture comes from the Latin verb ponere, which means "to put or place." The general concept of human posture refers to "the carriage of the body as a whole, the attitude of the body, or the position of the limbs (the arms and legs)." 
Webster's New World Medical Dictionary defines neutral posture as the stance that is attained "when the joints are not bent and the spine is aligned and not twisted. Neutral posture has given rise to the idea of achieving “ideal posture.” Ideal posture indicates proper alignment of the body’s segments such that the least amount of energy is required to maintain a desired position. The benefit of achieving this ideal position would be that the least amount of stress is placed on the body’s tissues. In this position, a person is able to completely and optimally attain balance and proportion of his or her body mass and framework, based on his or her physical limitations. Good posture optimizes breathing and affects the circulation of bodily fluids.
In medicine and occupations concerned with physical fitness, the concept of good posture is referred to as "neutral spine. In this context, proper posture or "neutral spine," is the proper alignment of the body between postural extremes. Deviations from neutral alignment are identified as excessive curvature or reduction in curvature. Rarely do these deviations in curvature occur in only one plane; however, they are typically referred to in this manner. In the anterior/posterior view, deviation from vertical results in abnormal lateral curvature of the spine called Scoliosis. In the sagittal view, excessive curvature in the cervical region is cervical lordosis, in the thoracic region thoracic kyphosis, and in the lumbar region lumbar lordosis. Reduction in curvature is typically termed flat back if present in the thoracic region and lumbar kyphosis if present in the lumbar region. In posture analysis, the spine is compared to a plumb line to detect the aforementioned abnormalities. From the anterior/posterior view this plumb line should run vertically down the midline of the body dividing it symmetrically into right and left halves indicating even weight distribution on left and right sides. From the sagittal view the plumb line should bisect the ear, odontoid process of C2, the cervical vertebral bodies, the center of the glenohumeral joint, the lumbar vertebral bodies, the center of the acetabulum, just posterior to the patella, and through the tarsals of the feet. This sagittal line of reference theoretically indicates even distribution of weight between the front and the back of the body.
Scoliosis is well established and even evaluated at an early age. It is typically quantified using the standardized Cobb angle method. This method consists of measuring the degree of deformity by the angle between two successive vertebrae. The Cobb method was accepted by the Scoliosis Research Society (SRS) in 1966. It serves as the standard method for quantification of scoliosis deformities. Sagittal plane posture aberrations such as cervical and lumbar lordosis and thoracic kyphosis have yet to be quantified due to considerable inter-individual variability in normal sagittal curvature. The Cobb method was also one of the first techniques used to quantify sagittal deformity. As a 2D measurement technique it has limitations and new techniques are being proposed for measurement of these curvatures. Most recently, 3D imaging techniques using computed tomography (CT) and magnetic resonance (MR) have been attempted. These techniques are promising but lack the reliability and validity necessary to be used as a reference for clinical purposes.
Posture assessment has also become quite popular in many practical environments like the personal training and sports conditioning settings. The need for reliable methods of posture assessment as a screening tool is warranted. Current available programs such as those through the National Posture Institute (NPI) and Posture Print are recommended for the practical setting but cost close to $1000 and may not be feasible for all practitioners.
Chronic deviations from neutral spine leads to improper posture. Increased stress on your back and causes discomfort and damage. When the spine is left in non-neutral posture for extended periods of time, it raises the diaphragm, preventing the body from taking a full breath. This can lead to reduced oxygenation throughout the body. It can also compromise the internal organs' performance by putting pressure throughout the abdomen. People who sit for long hours on the job are susceptible to a number of misalignments."
- A Patient's Guide to Rehabilitation for Low Back Pain: Understanding the Neutral Spine Position
- Marieb, E. N. (2001), Human Anatomy & Physiology, San Francisco, CA: Person Education Inc., Publishing as Benjamin Cummings, pp. 215–216
- Kendal, F. P.; McCreary, E. K.; Provance, P. G.; Rodgers, M. M.; Romani, W A. (2005), Muscles Testing and Function with Posture and Pain (5th Edition), Baltimore, MD: Lippincott Williams & Wilkins, pp. 49–65
- Definition of Posture, Webster's New World Medical Dictionary
- Definition of Neutral Posture, Webster's New World Medical Dictionary
- Danis, C. G.; Krebs, D. E.; Gill-Body, K. M.; Sahrmann, S. (1998), Relationship between standing posture and stability, Journal of the American Physical Therapy Association, pp. 502–517
- Webster, Deborah, The Neutral Spine, wellbridge.com
- Vrtovec, T.; Pernus, F.; Likar, B. (2009), A review of methods for quantitative evaluation of spinal curvature., European Spine Journal, pp. 593–605
- Kritz, E. N.; Croin (2008), Static Posture Assessment Screen of Athletes: Benefits and Considerations., Journal of Strength and Conditioning, pp. 18–27
- Roussouly, P.; Gollogly, S.; Dimnet, J. (2005), Classification of the Normal Variation in the Sagittal Alignment of the Human Lumbar Spine and Pelvis in the Standing Position, SPINE, pp. 346–353
- Vogel, Amanda (2001), Helping Clients Find Neutral Spine, ACE Certified News
- Markusic, Jeanne, Maintaining a Healthy Spine - Posture
- A Patient's Guide to Rehabilitation for Low Back Pain: Understanding the Neutral Spine Position. University of Maryland Medical Center Spine Program, June 19, 2008.
- Sitting straight 'bad for backs'. BBC News, 28 November 2006