One way to master stress is to be aware of your breathing. When
people feel panicked or unconsciously stressed, they tend to take
short, shallow gasps of air. The resulting lack of oxygen restricts
blood flow and causes muscles to tense. The way you breathe affects
your whole body. Full, deep breathing is an effective way to reduce
tension, feel relaxed, and reduce stress.
Breathwork  comprises a variety of stand-alone breathing techniques, as well as breathing techniques that are integral to other mind body practices, like qigong , tai chi, and yoga .
Many breathwork techniques are particularly useful because you can do them anywhere and anytime. Focusing attention on the breath also serves the meditative function of allowing the mind to more easily release distressing thoughts and emotions.
Dr. James Gordon's book Unstuck describes a technique used within a Mind-Body Skills group that is called Dynamic Meditation , which includes dynamic breathing. This breathwork is followed by movement/dancing and has been found by many to be pleasantly energizing.
By allowing more air to enter your body and focusing your attention so you calm the mind, you slow down your heart rate, lower your blood pressure, and break the stress cycle.
Breathwork is generally safe for people of varying physical fitness and age. However, make sure you breathe slow enough to avoid hyperventilation.
Gordon, James, MD (1996). Manifesto for a New Medicine: Your Guide to Healing Partnerships and the Wise Use of Alternative Therapies. New York: Addison-Wesley, http://www.cmbm.org .
Gordon, James, MD (2008). Unstuck: Your Guide to the Seven-Stage Journey Out of Depression. New York: Penguin Press.