12 Principles - 1 Squash and Stretch

The first principle of the Disney's 12 principles is squash and stretch of objects in the animation, which is the basic rule that must be applied when producing animation. It is common in daily life but as in animation, it is exaggerated into a certain degree, such as the example I've put, from the book the Animator's survival kit.

Applying the principle to characters with muscles is developed from the same principle but with arms and legs, which all follows the rule, the body of the character can be simplified into a ball, with the same property of the bouncing ball of the last example. In this piece of example the red lines clearly demonstrates the stretch of character's leg when landing and taking off in a jump cycle.