Final answer:
The major force-producing muscle for a specific movement is called an agonist or prime mover, such as the biceps brachii when lifting a cup, with the brachialis as a synergist and possible fixator.
Step-by-step explanation:
The muscle that provides the major force for producing a specific movement is called an agonist, also known as the prime mover. For example, when lifting a cup, the biceps brachii acts as the prime mover. However, it often receives assistance from the brachialis, which is then referred to as a synergist.
A synergist may also serve as a fixator, stabilizing the bone to which the prime mover is attached at its origin during the action of lifting the cup. On the contrary, the muscle that performs the opposite action of the prime mover is known as an antagonist, which helps control movements and maintain body positions.