Reinforced
Rinforzando, louder.
What it means
Verstärkt is the German equivalent of rinforzando and calls for a strengthening of the sound. What is meant is a rapid increase over a short stretch, not the long build-up of a crescendo and not the pinpoint emphasis of a single note.
Like all German performance markings, the word is not strictly defined. It names neither a starting nor a target value, but describes what is to happen. How far the strengthening goes results from the context and from the markings before and after it.
It is to be distinguished from anschwellend, which corresponds to crescendo and means a longer, even build-up. Verstärkt is shorter and more emphatic.
In the notation
The word stands below the staff, with vocal parts above the text, at the point from which it applies. It mostly refers to a few notes; afterward the previously indicated dynamic applies again. In German-language editions it replaces the Italian abbreviation, but more often it stands alongside letter signs and explains them.
Musical use
The marking is used to bring out a turn of phrase without changing the basic loudness of the section: a rising line with a goal note, a repeated figure with growing emphasis, an interjection in a secondary voice. In choral and song literature it stands over text passages that are to be stressed without the whole section becoming louder.
The instruction calls for a sudden strengthening of individual notes or groups, similar to rinforzando. It stands in German scores and is understood as a hint to bring out individual notes or voices. The increase in loudness is sudden, but not as sharp as a sforzando.
Performance practice
Distribute the increase over the notes concerned and direct it toward the goal note; an accent right on the first note is the most common confusion. Return afterward to the previous level — this is easily overlooked, and the section becomes unnoticeably louder and louder. Keep the tempo stable. And take care that the tone does not become hard: strengthening means more fullness, not more pressure.