Site-specific differences in vertebral spinous process inclination
In the cervical vertebrae, the spinous processes are horizontal, but as one moves toward the lower thoracic vertebrae, they become more vertical. Therefore, in the thoracic vertebrae, when the trunk is bent backward, the spinous processes overlap and interfere with the backward bending.

FlexionExtensionLateral flexionAxial rotation
Cervical vertebrae40˚75˚35-45˚45-50˚
Thoracic vertebrae45˚25˚20˚35˚
Lumbar vertebrae60˚35˚20˚