One of the secrets of the letter ו Vav is related to the shape of man. Vav is the letter of Zeir Anpin. The name of God that is related to this level is יוד-הא-ואו-הא, with numerical value of 45 that is the same for אדם, ‘man’.
The six sides of Zeir Anpin, as we studied previously, have 12 borders that reveal light. Six times twelve equals 72. When we divide the 72 into the three aspects of the Tree we get 24 channels for each.
Rabbi Ashlag explains that the six sefirot of Zeir Anpin form the shape of man. Chessed and Gevurah are the two arms. Netzach and Hod are the two legs. The body is Tiferet and Yessod.
The 72 channels in the body divided into three. 24 in the arms, 24 in the legs and 24 in the body.
Because the man, Zeir Anpin, is one unit, than from that aspect the three lines merged into one of 24 channels. The head has 6 channels and is held up by the body. The body has 18 channels, as the number of links of the Cervical and Thoracic vertebrae (upper spine).
Note: When a man immerses into the Mikvah it would be good to bend the head down and close to the knees similar to fetal position, arching the spine so the 18 links are moved. Then the body and head should be straighten up slowly as the head comes out of the water.
This action creates aspect of rebirth and revitalizes the body with spiritual energy. Where there is no Mikvah, this can be done in a large pool or any natural body of water that is big enough for this action.