rai wrote:regarding the Long Life practices and rites i was wondering
is the life force the same as "life sustaining wind"? then how is it possible that we can restore or gather the life force (which is something physical) just by chanting or visualization?
wouldn't it have more sense to do some yoga and improve our diet instead of doing long life practices?
Life force i.e. srog or jiv is connected with our tshe or ayus. Ayus refers to longevity, and to have a long life, we need to reinforce our jiv, our life force.
The reason we use an arrow during long life rites is that it is a symbol of the karmically projected span of our life i.e. in Abhidharma is states that longevity is like an arrow shot from a bow; and when the force impelling the arrow is exhausted, the arrow falls to the ground.
Now the principle of longevity is based on three factors: merit, karma, and life force itself. If you exhaust your merit you will die. If you meet with karmic circumstances, you will die. If you exhaust your lifeforce, you will die.
One's merit is a factor in one's longevity, and so therefore, when one's longevity is threatened, merit-making activities can reinforce it, thus practice. This can also theoretically delay a karmic disease and so on. Also since one's life force is physical, yoga, praṇayāma, diet, and so on can reinforce it.
To answer your first question -- no, Jiv is not the same thing as praṇā vāyu; however, without breathing you will quikly die, and so respiration is called "life sustaining" vāyu or wind. Jiv is assciated with the heat of the body. When you cease breathing, your body slowly loses its heat which is the sign that you have lost your life and your life force is gone. Actually, your body starts losing its heat even before you die, and coldness in the extremities is a sign of death. You can read about signs of death, both distant and near in texts on the bardo as well as in the chapter on the signs of death in the translations of the medicine tantra.
Almost all major cycles of long-life practice have praṇāyāma, rasāyāna and dietary recommendations, and all
systems of yoga are oriented towards disease prevention and life-extension. So long life practices are a perfect combination of religious practice, yoga and diet which serve to extend life.