Final answer:
The back muscles are categorized into intrinsic, intermediate, and extrinsic groups. The extrinsic muscles are involved in the movement of upper limbs and respiration, while intrinsic muscles primarily facilitate vertebral column movement and maintaining posture.
Step-by-step explanation:
The muscles of the back are divided into three groups: intrinsic, intermediate, and extrinsic muscles. The extrinsic muscles include those that are involved in movements of the upper limb and in respiratory movements, such as the trapezius and the latissimus dorsi. They are distinct from the intrinsic back muscles, which are primarily responsible for movements of the vertebral column and include groups like the erector spinae.
Intrinsic muscles of the back are capable of moving the vertebral column and maintaining posture. The intrinsic group is further categorized into the splenius, erector spinae, and transversospinales muscles, along with smaller segmental muscles. The intermediate muscles, like the serratus posterior superior and inferior, assist in respiratory movements but are not significant movers of the vertebral column.
Therefore, in response to the question, the muscles of the back are divided into three groups: intrinsic, intermediate, and extrinsic.