The position of the spine is commonly discussed in relation to a good posture, with a "neutral" spine position being the ideal.
A neutral spine is when the all the vertebrae are in a natural position, under the minimal amount of stress.
When seen from the front or back, all vertebrae in a neutral spine form a straight line.
All vertebrae are aligned to create the median plane, with the body balanced either side.
The nuchal and supraspinous ligaments that attach to the posterior (back) of the spine are also aligned.
When seen from the side, a neutral spine is curved.
For a neutral spine, the rectus abdominis muscles need to be "long and strong", fully extended and taking the strain between pelvis and chest. If the rectus abdominis muscles are not fully utilised the lateral abdominal, psoas and other muscles of the lower back bear the burden which has negative effects on the positioning of the lumbar spine.
The gluteus maximus positions the sacrum, linking the base of the spine to the pelvis.
The trapezius muscles must be free of physical restrictions to allow the correct positioning of the thoracic and cervical spine and alignment of the nuchal and supraspinous ligaments.