In humans, the back consists of seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, five sacrum vertebrae and the tailbone. The vertebrae are separated from each other by an intervertebral disc or discus. In the middle of your spine runs your spinal cord and nerves that control your arms, legs and torso.
In the spine there is an S shape. This S shape gives the spine flexibility and stability. This S shape also ensures a natural shock absorption. For each person, the S shape is different. The size of the S shape has little correlation with complaints.
It is true that if you cannot actively influence the S shape, for example by stretching your upper back, this can lead to complaints.