★How to draw back
　The movement of the back muscle

■Draw the back

To understand the structure of the back is very difficult.
Please note the movement of the shoulder blades (Scapula).

＠Deltoid ＠Infraspinatus ＠Teres major ＠trapezius ＠Latissimus dorsi

＠Supraspinatus ＠Rhomboid ＠Levator scapulae ＠Serratus anterior

Photo of the movement of the back.