For the CV4 technique the practitioner will contact the participant's occiput (lateral to the external occipital protuberances, but medial to the occipital-mastoid suture) with his or her thenar eminences. When no cranial mobility will be found, operators will be free to use any kind of technique to enhance the cranial movement before CV4 procedure. Once the practitioner will detect the CRI, the practitioner will resist the flexion phase of the CRI and exaggerate the extension phase. This compressive pressure will be maintained until the CRI stopped, and the still-point is reached. The still-point will be held until the CRI return, at which point the compressive pressure will be slowly release. For the sham CV-4, The operator will overlap the hands so that the thumbs formed a "V". The operator's thenar eminences will contact the occiput very lightly well below the positioning used in the CV4 procedure but with no pressure on the occiput between the occipitomastoid sutures. Once placement will be achieved, the operator's hands will remain motionless for 10 min. Finally, the practitioner's hands will be gently removed and the participant's head will be placed on the table for both procedures.