Back muscle building:
Your back is made up of three major muscle groups. The latissimus dorsi is located on each side of your back and helps you extend, rotate, and pull your arms toward your body.
The erector spine (lower back) is made up of three muscles that run the length of your back from your neck to your fanny.
The erector spine is involved in flexion and extension of the upper body, as well as rotation.
The rhomboids (major and minor) are between the shoulder blades and aid in rotation, elevation and retraction of the shoulder blades. These are also known as your 'posture' muscles
The deep muscles of the back (intrinsic muscles) are responsible for keeping the body in the erect position during the waking hours, whether sitting or standing.
You can imagine the amount of work that is placed on these muscles and why one of the population's most annoying medical problems is a painful back. You can also imagine how much money is spent to correct back problems.
A correct posture and careful use of the back in carrying or picking up heavy objects is all that is necessary to allay most of back problems. The erector spine group of muscles are the strongest muscles in the back and take on most of the work. The deep back muscles are both extensors and rotators of the axial skeleton