Which of the following best describes the function of synergist muscles?

Synergist muscles play a vital role in movement by assisting the prime mover, also known as the agonist. When a primary muscle contracts to produce movement, synergists help by providing support and enhancing the efficiency of that action. They can also help to fine-tune the movement and ensure it occurs smoothly and effectively.

In many exercises, especially compound movements, numerous muscles work together rather than in isolation. The synergists help to stabilize the joint and maintain proper alignment, allowing the prime mover to operate with optimal effectiveness. This collaboration is crucial for actions such as lifting, pushing, or pulling, where precise control and strength are needed.

While stabilizing muscles and joint initiators are important in movement, the unique role of synergists specifically involves assistance to the primary muscle during an action, which is why this answer best describes their function.