Muscles must be arranged in antagonistic pairs, because when a muscle contracts:
A)it lengthens and pulls at the same time
B)it can only push a bone in one direction
C)it pulls one way and pushes another
D)it can only pull a bone in one direction

Question

Quizplus · Accepted Answer

When a muscle contracts, it can only pull the attached bone(s) in one direction. Therefore, in order to move a bone in both directions (e.g. flexion and extension of the arm), two muscles must be arranged in opposing pairs so that one can contract to pull the bone in one direction while the other relaxes and allows the bone to move in the opposite direction. This is why muscles are arranged in antagonistic pairs. Choice A is incorrect because a contracting muscle shortens, not lengthens. Choice B is incorrect because a muscle can push a bone, but it can also pull a bone. Choice C is incorrect because a muscle can only exert force in one direction, not both pulling and pushing simultaneously.

Muscles Must Be Arranged in Antagonistic Pairs, Because When a Muscle