The main action of the quadriceps or "quads" is walking. This muscle helps straighten the knee and maintain posture. Without this muscle, running, walking, and even standing would be quite impossible.
antagonist muscle
THe action of the digastric muscle is to depress the mandible or evaluate the larynx
The frowning action.
gdg
It represents contracting or shortening of a muscle.
rectus femoris
Reflex action
brachioradialis
a concentric muscle action.
infraspinatus muscle
A antagonist muscle is a muscle that opposes the action of another muscle. The Triceps Brachii is the antagonist of the Biceps Brachii.
The Agonist muscle. In contrast, the muscle group that has passive action(the muscle being stretched) is called the antagonis muscle. For example, when doing a bicep curl. Your biceps are the agonists and your triceps would be the antagonists.