What term describes muscles that work in opposition to the primary moving muscle?

The correct term for muscles that work in opposition to the primary moving muscle is "antagonists." When one muscle contracts to produce movement, the antagonist muscle relaxes to allow this movement to occur. For example, during a bicep curl, the biceps act as the primary muscle (agonist) that performs the movement, while the triceps act as the opposite muscle (antagonist), which must relax to enable the lifting motion.

Understanding the role of antagonists is crucial in designing effective strength training programs since balanced development of agonist and antagonist muscles can help maintain joint stability and prevent injuries. Recognizing this relationship also aids trainers and clients in executing movements correctly and safely, enhancing overall performance in various physical activities.

The other terms have distinct meanings; synergists assist the primary muscle during movement, agonists are the primary movers, and leverage refers to the mechanical advantage gained in movements, but none of them accurately describe the opposing muscle role as antagonists do.