Complex sentence: They may show specific types of movement such as waxy flexibility, in which they maintain positions after being placed in them through someone else in which they resist movement in proportion to the force applied by the examiner.
Split into simpler sentences: They may show specific types of movement such as waxy flexibility, in which they maintain positions after being placed in them by someone else. Conversely, they may remain in a fixed position by resisting movement in proportion to the force applied by the examiner.