The central feature of the human back is the vertebral column, specifically the length from the top of the thoracic vertebrae to the bottom of the lumbar vertebrae, which houses the spinal cord in its spinal canal, and which  enerally has some curvature that gives shape to the back. The ribcage extends from the spine at the top of the back (with the top of the ribcage corresponding to the T1 vertebra), more than halfway down the length of the back, leaving an area with less protection between the bottom of the ribcage and the hips. The width of the back at the top is defined by the scapula, the broad, flat bones of the shoulders.
Spine has a “S-type” curved in order to be good at using hands as well as upright walking. Intervertebral disk between spines can play an important role of absorbing & softening shocks, also can prevent shocks from being propagated to brain while walking or running. Incorrect posture & action can cause imbalance of spine, neurosurgeries & orthopedic diseases.