I looked at how Disney animators are taught life drawing to help them in creating life like gestures and postures in animations and use these to create unusual/individual character traits. These youtube clips below, shows how animators filmed a live action (with actors) sequence and traced over it frame by frame to create more realistic movements through drawings.
This video above is likely a promo film for the Disney studios, but I’ve read that this was a technique used for Sleeping Beauty as well as various features previously to this such as Snow White and the seven dwarfs, Alice in Wonderland (see video below) and various scenes for films during the ‘renaissance age’ of Disney in the late 80’s and through 90’s, such as the Little Mermaid (also below).
Animators who use this technique have to become used to using the drawing style that forms continuity between each artists work and final film product (Disney style of drawing) whilst also making sure they keep to the form of actor in the frame they’re tracing, but also making sure they draw the relative parts of the animated character correctly! This type of drawings is a lot more detail oriented to make sure that, in the final film, you don’t see Ariel’s eyes change shape in odd scenes, or her hair changing length. Making sure that Disney’s high standard of animation continues.