Background

Yoga is an ancient technique practiced by sages and yogis as a desirable and healthy way of life. The very meaning of yoga is to achieve a balance within the internal and external environment, thereby seeking to attain mental, spirit- ual and physical well-being. This is made possible through the practice of "Pranayama" or breathing exer- cises, "Asana" or specific postures, and Meditation [1]. It is thought that practicing yoga over a period of time leads to a decrease in respiratory rate, muscular relaxation along with calming of the mind, which might be interpreted at least partly as a decreased state of arousal [2,3]. Many acute studies have demonstrated that Transcendental Meditation, Zen Meditation, Om Meditation, and Yogic Relaxation reduce the resting oxygen consumption rate, respiratory rate, heart rate, and the spontaneous galvanic skin response [4-8]. These changes are thought to be due to decreased arousal as well as decreased mental and mus- cular activity. It should be noted that the findings referred to above, particularly with reference to meditation, are different from those found during sleep, to the extent that these are observed in a wakeful relaxed state, and usually in the sitting posture.
In contrast to the reduced physiological and metabolic activity observed during meditation and relaxation pos- ture types of asana, pranayamas and other specific asanas could acutely increase the metabolic rate. An increase of 19% in oxygen consumption has been observed during the practice of one type of pranayama called the Ujjayi Pranayama [9]. Breathing through a particular nostril, while performing the Surya Anuloma Viloma (right nostril breathing), has been shown to increase oxygen consumption by 28% [7]. Other specific asanas can also increase the metabolic rate transiently over the short term [10,11]. The increase in oxygen consumption during these yogic practices is due the muscular activity associated with the posture assumed during the asana, or due to an increase in voluntary deep inhalation and exhalation during the pranayama [9].
There are at least two questions that arise from these findings. First, yoga practitioners usually combine techniques such as pranayama, asana as well as meditation in their daily yoga practice. While the acute effect of each of these techniques has been documented, the combined effect of these practices, with their stimulatory or inhibitory effect on the BMR, is unknown. Second, the experiments referred to above have documented the acute effect of yoga practices on the oxygen consumption. From a daily living viewpoint, it is desirable to demonstrate the effect of a long-term combined yoga routine on the BMR. There- fore, the primary aim of this study was to answer these questions by studying the effect of a long term (six months or greater) practice of combined techniques of yoga, on the BMR of young to middle aged men and women.