Antagonistic muscles are pairs of muscles that work opposite to each other to control movement in the body. When one muscle in the pair contracts, the other relaxes to allow smooth and coordinated movement. These muscles work together to create balance and control over joint motion.

For example:

1. In the arm, the biceps and triceps are antagonistic muscles. When the biceps contract (causing the elbow to bend), the triceps relax. Conversely, when the triceps contract (causing the elbow to straighten), the biceps relax.

2. In the legs, the quadriceps (front of the thigh) and hamstrings (back of the thigh) are antagonistic. When the quadriceps contract to extend the knee, the hamstrings relax, and when the hamstrings contract to flex the knee, the quadriceps relax.

This balanced relationship between opposing muscles is essential for smooth, controlled movements and for maintaining proper posture and joint stability.