gdg
antagonistic muscle action.
muscles relaxes
When the lungs are expanded, this action takes place due to the diaphragm contracting during inhalation. During exhalation, the diaphragm relaxes.
The bicep muscle. The tricep contracts to straighten the arm as the bicep relaxes.
Relaxes
contract
When you bend your elbow, the biceps muscle contracts. At the same time the antagonist muscle, that is the triceps muscle relaxes in synchronized manner. Vise verse action take place, when you straighten the arm at the elbow. Triceps contracts and biceps relaxes.
When you experience a leg or muscle cramp, it is because the muscle has constricted or tightened up. The lump you are referring to is the muscle itself that has tightened up. When your muscle relaxes, the cramp goes away.
the smooth muscle
I think what your after is called an antagonistic pair of muscles, for example the bicep and the tricep. When the bicep is contracting the tricep relaxes and when the tricep is contracting the bicep relaxes.
It Contracts
antagonist.