What is the effect of a synergist muscle during an exercise?

A synergist muscle plays a supportive role during an exercise by assisting the prime mover (the muscle primarily responsible for a specific movement). By enhancing the overall force and stability of the movement, synergist muscles contribute to more efficient and controlled motion. For example, when performing a bicep curl, the biceps act as the prime mover, while muscles like the brachialis and brachioradialis serve as synergists, aiding in the flexion of the elbow. This collaboration allows for smoother execution of the movement and can help reduce the risk of injury by maintaining joint stability.

In contrast, other options describe functions that do not align with the primary supportive role of synergist muscles. For instance, preventing movement or creating resistance would not foster the coordinated effort needed for effective exercise. Similarly, weakening the action contradicts the essential supportive function of synergists, which aim to enhance the movement rather than diminish it. Thus, the role of synergist muscles is crucial for optimizing performance during various physical activities.