Question

What are antagonistic muscles? Give one example.

Answer 1

Once a structure has been moved by a muscle, it cannot return to its original position without another muscle acting on it. Muscles that cause opposing movements are known as antagonistic muscles.

Example of antagonistic muscles:

When you flex your arm at the elbow, the muscle that lies above the upper arm, i.e. the biceps is seen and felt bulging. This muscle bulges due to contraction and becomes smaller in length, stiffer and thicker. Contraction of biceps draws the forearm towards the upper arm. However, relaxation of biceps cannot push the forearm back to its original position. When the arm is extended or straightened, the muscle at the back of the upper arm, i.e. the triceps contracts. The two muscles work antagonistically or in opposite directions to bend or flex and straighten the arm at the elbow. 

Answer 2

1. Muscles often work in pairs which work against each other. These are called antagonistic pairs.
2. The muscles in the upper arm control the bending and straightening of the arm.
3. The two muscles, the biceps, and triceps are working against each other.
4. When the biceps contract the lower arm is raised and the arm bends.
5. In this position the triceps muscle is relaxed.
6. To straighten the arm the reverse happens.
7. The triceps contract straightening the arm, while the biceps relaxes.