Effects of Voluntary Neck Extension on Cerebral Blood Flow, in Breath-hold Divers Ending an Apnoea of Two Minutes or More.

Inclusion Criteria: * Major (≥18 years), under the age of 51 * Male * Can hold an apnea of 2 minutes or more * Practicing for less than 2 years the apnea at the rate of at least 10 sessions of apnea in the year * Not having a known cardiovascular history : any form of heart rhythm disorder, Ischemic heart disease, angina, arteriopathy, any valvular pathology, high blood pressure ... * No known respiratory history (asthma, Chronic Obstructive Pulmonary Disease, bronchiectasis, pulmonary emphysema, pneumothorax, pleurisy, pulmonary infection, lobectomy ...) * No neurological history of type: epilepsy, deficit syndrome, iterative loss of knowledge, recent head trauma with loss of consciousness Exclusion Criteria: * \- Minors and persons over 51 years of age * Person under curators or trusteeship * Person with a history of cardiovascular, respiratory or epilepsy as cited by the French Federation of Study and Submarine Sports, which poses as a contra-indication to the practice of apnea: Cardiac insufficiency, Obstructive Cardiomyopathy, syncopal risk pathology (valvulopathies type aorting narrowing or mitral narrowing), paroxysmal tachycardia, non-paired auriculo ventricular block 2/3, stroke, uncontrolled hypertension after stress test, recent infarction, angina, pericarditis. Asthma stage 3, severe Chronic Obstructive Pulmonary Disease, bronchiectasis, pulmonary emphysema, pneumothorax, pleurisy, pulmonary infection, lobectomy ...) Epilepsy, deficit syndrome, iterative loss o…