Muscles work by either contracting or relaxing. The movement that they cause is dependent on the structure that they are attached to e.g contraction of the biceps causes the arm to bend upwards due to the attachment of ligaments.
synergistic muscle
A synergist muscle is a muscle that aids another by promoting the same movement.
Isotonic contractions are the type that involve muscle movement. This movement is due to a change in length as the muscle fibers shorten or lengthen.
the word voluntary muscles
muscle
synergist
muscle spasm
contraction
movement
mus musculus (as it appeared to the ancients that there was a small mouse-like movement - especially in the biceps muscle).
hypertrophy
dystrophia