Vocal Warm-ups by Klaus Heizmann, 200 exercises for Choral & Solo Singers. The human voice is the most sensitive & delicate of all instruments. Only with careful & responsible use over the years can it be kept healthy & strong. Choral voice training & these warm-up exercises can make a valuable & long-lasting contribution to achieving this goal. The importance of these warm-up exercises must repeatedly be explained to singers. They are just as important as the warm-ups an athlete does.