On the big screen, the antagonist typically plays a devious role. His or her goal is to undermine the lead character, creating drama and conflict. But in the weight room, it's a different story. Every time you perform a movement—whether it’s a squat, curl, press, row, raise, lunge, deadlift, or dip—all of your muscles, including the “antagonists,” work together to get the job done.

In the context of your body, an antagonist is a muscle that opposes the action of the targeted muscle. When you do a dumbbell curl, your triceps are the antagonists, for example. Their primary job is to extend the elbow, but they relax enough to allow your biceps (i.e., the “agonists”) to flex your elbow and lift the weight while still producing enough opposing force to kelp keep the movement controlled. When you do a triceps extension, the roles are reversed—your biceps are the antagonists and your triceps are the agonists.