ANTAGONISTIC MUSCLE

Antagonistic muscles are two sets of muscles which contracts in opposition to each other to move bones at joints.

Pairs of muscles that work together to allow coordinated movement of the skeletal joints in human.

Meaning that :
When one muscle contracts, the other muscles will relaxes.

One muscle pulls the bone in one direction, and the other muscle pulls it in the opposite direction.

In human; The biseps and triceps muscles are a good example to explain the concept of antagonistic muscles.


The bending of the upper limb / forearm :
When the biceps contracts,
the tendons will transmit the pulling force (produced by the contraction) to the forearm.
At the same time, triceps relaxes.
As a result, the elbow joint will bends, and the forearm moves upwards.

The straightening of the upper limb :
When the triceps contracts,the tendons will transmit the pulling force to the forearm.
at the same time,the biceps will relaxes,
the forearm is straightened / moves downwards.

If you get injured, we can see clearly the structure inside our body. All these pictures show it, but for those who are not brave enough, please don't see...

Knee ligaments injury

A broken forearm

Injury after a shooting attack

(http://clearharmony.net/articles/200408/21472.html)