How do muscle pairs work together to create movement?

Muscle pairs work together in a complementary fashion to facilitate movement through the opposing actions of flexion and extension. In this context, one muscle in a pair, often referred to as the agonist, contracts to cause movement at a joint, while its partner, known as the antagonist, relaxes or lengthens to allow that movement to occur. For example, when the biceps muscle contracts to flex the elbow, the triceps muscle similarly relaxes to permit that movement. This coordination between agonist and antagonist muscles is essential for smooth and controlled movements in the body.

The other options do not accurately depict the functionality of muscle pairs during movement. For instance, suggesting that one muscle contracts while the other remains static overlooks the dynamic nature of muscle interactions in movement. Additionally, the idea that both muscles contract equally at all times fails to recognize the alternating roles of agonists and antagonists. Lastly, while alternating contractions can help prevent fatigue, the fundamental mechanism of movement relies primarily on the opposing actions of flexing and extending around a joint.