You can purchase the official PDF directly from the (often via Gumroad or their own store). It is also bundled with their book "Anatomy for Sculptors: Understanding the Human Figure."
Most anatomy books show the arm in a standard "anatomical position" (palms facing forward, arms slightly abducted). This is useless for action scenes. The human arm is a kinetic chain. When the hand moves 10 degrees, the radius rotates over the ulna, the biceps brachii twists, and the brachioradialis fires. arm and hand in motion by anatomy for sculptors pdf
: You can buy the digital version or bundles at the Anatomy For Sculptors Store . You can purchase the official PDF directly from