In addition to the effects of Yoga mentioned in Pt I, I want to add the following. Yoga usually involves deep and even breathing, the slow and controlled contraction and release of the diaphragm, together with, at least in the case of Ujjayi breathwork as taught by Sri Krishnamacharya, the maintained contraction of abdominal muscles (Bandha), act to expand the rib cage on inhale, and contract the abdominal cavity on exhale. The inhale stimulates nerves in the chest which are related to feeling good, think of how a good yawn and back stretch makes you feel, at the same time the diaphragm pulls down on the heart and creates a twisting massage effect through its attachment to the pericardium, this rhythmic “milking” of the heart also creates beneficial emotional and physiological effects. As the diaphragm contracts and encounters an abdominal cavity that is held in place by the bandha, it literally squashes the liver and stomach and other viscera, aiding in the flow of blood and maintaining tissue freedom and physiological function, a bit like squeezing a sponge in a fresh water stream, stagnant blood is flushed out and fresh blood allowed in. The same effect is seen on the out breath but for the lower abdominal organs, especially if this is combines with flexion of the trunk. In this way , the inner organs and abdominal cavity all receive a healthy massage and work out, maintaining correct function and relationship to each other, and so less risk disease and feeling un well.
Another aspect of Yoga is slightly more esoteric, as we maintain our mind on the breath we develop an intimate relationship with life. Including the body and the heart, and the opposites of up down, in out, left right into this intimacy, we create a kind of energetic harmony and closeness, intimacy and harmony, which liberates energy which spills out into our social relations. As we are with ourselves, so we are with others. Intimacy is the undivided state, wholeness, which brings with it feelings of safety, security and joy.
These are some of the ways in which Yoga brings happiness, it is accessible to everyone, all you need is to be able to breathe.
Thank you .