The basic action of any muscle is contraction, which occurs when muscle fibers shorten and generate force. This contraction is initiated by the nervous system, causing the muscle to pull on bones or other structures, resulting in movement. Muscles can also relax, returning to their original length, which allows for coordinated and controlled movements in the body.
Contraction
muscle fiber
The primary mover.
antagonist muscle
The myofibril is the basic muscle cell, within which is the sarcomere, the basic unit of muscle contraction.
THe action of the digastric muscle is to depress the mandible or evaluate the larynx
Any physical action that you do can give you muscle. You don't necessarily need weights to gain muscle. Simple things like push ups can still give you muscle.
The basic "principal" behind somatic motor pathways is a pathway from your "brain" or regions in or near the brain where nerve impluses travel from and go to skeletal muscle to cause a muscle contraction. (It's complicated, but doesn't get any more basic than this) -Jordan Bourne
The frowning action.
gdg
It represents contracting or shortening of a muscle.
rectus femoris