A vocal warm-up is a series of exercises that prepare the voice for singing, acting, or other use.
There is very little scientific data about the benefits of vocal warm-ups. Relatively few studies have researched the effects of these exercises on muscle function and even fewer have studied their effect on singing-specific outcomes.
A good vocal warm up should accomplish five things: a physical whole-body warm-up, preparing the breath, preparing the articulators and resonators, moving from the spoken register to the singing register (or an extended spoken register for acting), and preparing for the material that is going to be rehearsed or performed.
Physical whole-body warm-ups help prepare a singer or actor's body in many ways. Muscles all over the body are used when singing/acting. Stretching helps to activate and prepare the large muscle groups that take care of balance and posture, and the smaller muscle groups that are directly involved with breathing and facial articulation. Stretches of the abdomen, back, neck, and shoulders are important to avoid tension, which influences the sound of the voice through constriction of the larynx and/or breathing muscles. Actors (including opera singers or musical theatre performers) may need to do a more comprehensive physical warm-up if their role is demanding physically.
Preparing the breath involves not only stretching the many muscles involved with respiration, but preparing them to sustain exhalation during long singing/speaking passages. Specific training of the respiratory muscles is required for singers to take very quick deep breath and sustain their exhalation over many bars of music. A good vocal warm-up should include exercises such as inhaling for 4 counts, then exhaling for 8 counts (and slowly transitioning until the performer can inhale for 1 count and exhale for as long as possible); panting or puffing air are also used to engage in the intercostal muscles.