Synergist muscles are those that assist the primary muscle, known as the agonist, during a movement. They help stabilize joints and ensure smooth motion by working together with the agonist. For example, during a bicep curl, the brachialis and brachioradialis act as synergists to support the biceps brachii. These muscles play a crucial role in enhancing strength and coordination. By working in concert, synergist muscles help distribute the workload, reducing the risk of injury and improving overall performance. Understanding their function is important for effective training and rehabilitation strategies.