During the vocal warming up, the singer should sense one’s voice resonating from the depth of one’s throat, and the rear of one’s oral cavity. The warming up exercises should include a contraction and a release of one’s voice-producing muscles, alternately, with an 8-second contraction followed by an 8-second rest.
A commonly made mistake is an over-strained vocal warming up without a rest, since vocal warm-up is essentially about relaxing, not straining the voice-producing muscles before they get warm!

Faithfully keeping your voice intact
Talya