A prime mover, in the context of the muscular system, is the main muscle responsible for producing a specific movement during an action. It works by contracting, while its antagonist muscle relaxes, to achieve motion at a joint.
Related terms
Antagonist Muscle: The muscle that opposes the action of the prime mover and must relax to allow the prime mover to contract effectively.
Synergist Muscle: A muscle that assists the prime mover in performing its action, often by stabilizing joints or adding extra force.