As stresses on the back increase from the cervical to lumbar regions, lower back problems are common.
Muscles of the back consist of extrinsic and intrinsic groups:
The extrinsic muscles of the back move the upper limbs and the ribs.
The intrinsic muscles of the back maintain posture and move the vertebral column; these movements include flexion (anterior bending), extension, lateral flexion, and rotation (Fig. 2.3).