According to his own report, what Garcia was looking for was a precise, instantaneous and clean-cut tone quality that emerged at the moment of tonal inception rather than “settling in.” While this kind of tonal initiation is most desirable, it does not occur because of a precise setting of the vocal folds, although that is a definite factor, but because the entire vocal mechanism, particularly a proper laryngeal suspension, has taken form simultaneously. Unless the vocal muscles are inhibited in their movement because of psychological rigidities that arrest their motility, it can be demonstrated that the coup de glotte is an instantaneous movement from rest to balanced tension which finds the larynx being positioned with the utmost speed and precision, much like the skilled violinist who touches the bow to the string without having to ease into the correct stroking.

[…]

The problem with the coup de glotte, apart from Garcia’s poor choice of words, is that it has always been judged from a “how do you do it” viewpoint. For this reason it has been rightfully condemned almost from the time the idea was first promulgated. The misconception of singing as something one “does” is dramatically illustrated when attempting to execute a trill on an interval of a second. Physically and neurologically this is impossible unless the mechanism is precisely tuned and the action is reflexive. All singing should be of this kind. To “do” in the form of “acting upon” implies foreknowledge, and this knowledge in a practical sense is secreted within the organic systems.

Reid, Cornelius L. Essays on the Nature of Singing. Recital Publications, 1992.