The most physical of the four methods powering yogic practice is commonly known as Kundalini awakening. In this method the latent energy of the genitals is connected to the brain via the spine and this greatly enhances the energetic capacity of the practitioner, which by extension allows them to do things meditatively/yogicly that they could not previously accomplish.
Additionally, it improves whole body movement, endocrine system function, lowers the threshold for adrenal release, improve strength, improves speed and some would argue it makes you smarter. From practical experience, I would suggest that it allows for the storage and retrieval of information at a much quicker rate which can give the appearance of enhanced intelligence.
Kundalini awakening occurs when this latent energy explodes from the base of the spine, although some people describe it as coming from the feet if it occurs while standing, propagates up the spine and explodes out of the top of the head. At this point the practitioner experiences a series of visions and/or a state of expanded consciousness that corresponds with most descriptions of enlightenment. Afterwards, the body goes through a series of physical transformations in which it becomes accustomed to this higher level of energetic functioning. This can take a period of several years.
The safer systems of this kind typically visualize the movement of vital energy starting at the base of the spine, going up the back, over the top of the head, down the front of the body and ending at the base of the spine in a kind of loop. Certain joint and body locks are performed to enhance the effect, placing the tongue behind the front teeth being the most common, and this is performed for 3-4 hours a day for up to 100 days to generate the effect.
Primarily, these techniques open the subtle lines of force, sometimes called meridians, within the body and allow for a stronger movement of energy. Some argue this technique also causes energy to become denser within those lines of force versus simply creating a groove for movement of energy within the body. I am unclear on this issue myself, but the technique does in fact work.
A great book on the topic is Path Notes of an American Ninja Master by Glenn Morris. And his surviving school can be found at www.kundalniawakeingprocess.com .