The precise mechanism of vocal fold vibrations during phonation is not well known. At present it is impossible to say whether this movement is active or passive. Since the studies of MacLeod & Louis Sylvestre, we know that the vocal muscle is asynchronous and, so, can have a fast oscillatory movement induced by a continuous depolarization of the muscular fibre membranes. Thus, we believe at present that the glottic opening can be merely passive and that the closing can be both passive and active through a myogenic mechanism. The purpose of this work was to try to establish whether this concept is right, by recording simultaneously the aerodynamic forces acting upon the vocal folds and their acceleration during phonation. This acceleration represents the forces applied to the vocal folds as a function of time. By comparing the temporal evolution of the two forces we can assert that glottic opening is a passive movement. This protocol does not allow us to know if closure is due solely to the elastic retractive force, or also to a muscular, active force such as myogenic rhythm. To answer this question we must use another protocol.