The High Pull is a large % of the major muscles of the body. The "triple extension" of the ankle, knee and hip joints involve the calf plantar flexor muscles (gastroc and soleus), knee extensors (quadriceps), and hip extensors (hamstrings and gluts). The torso is stabilized by the quadratus lumborum and spinal erectors. The traps control the final "shrug" with the deltoids and elbow flexors assisting.

You also have muscles active isometrically to maintain the grip on the bar. Most of the above are muscle groups, so if you count them individually you have dozens of muscles throughout the body involved in the high pull. Thus, I call it a total body exercise.