What are the physiological effects of meditation?The most common physiological effects of meditation are reduced blood pressure, lower pulse rate, decreased metabolic rate and changes in the concentration of serum levels of various substances.
When I meditate I experience physical pain in my body. What should I do?The point of practicing meditation is to develop mindfulness. The object of meditation isn’t all that important, although the breath is a good object since it is always available, simple and peaceful.
But if it’s difficult for any reason or something like pain comes up, then focusing on that is possible too. The practice of walking meditation (paying attention to the sensations at the feet as you walk from one point to another and then back again) is also very good and can be mixed in with sitting meditation over a period of an hour (35 minutes sitting, 25 minutes walking, say).
Sensations (itching/aches/pains) can arise in the body when meditating for several reasons. Sometimes the cause is just an uncomfortable posture make sure that your posture is comfortable under normal circumstances. Other times the cause is that sensations in the body are more noticeable in meditation. The body and mind are calmer and you are able to notice more details in your bodily experience. It is often interesting to simply observe these sensations in your body to use them as the objects of meditation. Sometimes these sensations just go away without your having to move or change your posture. Remember that a quiet body contributes to a quiet mind.
One technique you might try is taught by S. N. Goenka. Their web site is: http://www.dhamma.org/. Although I couldn’t find specific meditation instructions there, I know that the practice that is taught in that tradition is primarily awareness of the body. You learn to focus on different parts of the body and “Sweep” your attention through it.