Sometimes the postures in which artists freeze their subjects to gain the most animated effect are not even found in the real world. Galloping animals like horses are often depicted with both fore and hind legs outstretched. Quadrupeds only adopt such postures when leaping and never when running. But the depiction of rapid movement requires the full extension of the limbs even when such extension is unreal.
– Rudolph Arnheim, Art and Visual Perception