Chaya M S, Nagendra H R

ABSTRACT

Background: The metabolic rate is an indicator of autonomic activity. Reduced sympathetic arousal probably resulting in hypometabolic states has been reported in several yogic studies.
Aim: The main objective of this study was to assess the effect of yoga training on diurnal metabolic rates in yoga practitioners at two different times of the day (at 6 a.m. and 9 p.m.).
Materials and Methods: Eighty eight healthy volunteers were selected and their metabolic rates assessed at 6 a.m. and 9 p.m. using an indirect calorimeter at a yoga school in Bangalore, India. Results and conclusions: The results show that the average metabolic rate of the yoga group was 12% lower than that of the non-yoga group (P < 0.001) measured at 9 p.m. and 16% lower at 6 a.m. (P < 0.001). The 9 p.m. metabolic rates of the yoga group were almost equal to their predicted basal metabolic rates (BMRs) whereas the metabolic rate was signifi cantly higher than the predicted BMR for the non-yoga group. The 6 a.m. metabolic rate was comparable to their predicted BMR in the non-yoga group whereas it was much lower in the yoga group (P < 0.001). The lower metabolic rates in the yoga group at 6 a.m. and 9 p.m. may be due to coping strategies for day-to-day stress, decreased sympathetic nervous system activity and probably, a stable autonomic nervous system response (to different stressors) achieved due to training in yoga.
Keywords: Basal Metabolic Rate (BMR); decreased arousal response; yoga; yoga training.

An understanding of metabolism at different times of the day has significant implications due to its link to sleep, health, stress and fatigue, ultimately determining the quality of life. BMR is the lowest (basal) metabolic rate measured just after waking from a night s sleep.  It is well known that sleep is a restorative process wherein the body synthesizes its necessary chemicals for growth, maintenance and development. Rejuvenation and repair take place during sleep. Sleep generally brings down the metabolic rate by about 10%.  Low basal metabolic rates of yoga practitioners have been reported. Hypometabolic states have been reported in yogic studies wherein short and immediate effects of meditation and relaxation were observed.
Yoga which is a way of life is characterized by balance, health, harmony and bliss. In yoga lore, three normal states of consciousness have been identified-they are wakeful state (jagratha), dream or rapid eye movement (REM, swapna or dream state) and deep sleep without dreams (sushupti). Meditation is a part of yoga which is the seventh limb of Astanga yoga[11]—a state of alert rest as stated by Maharshi Mahesh Yogi.[12] This leads to superconsciousness or the fourth state of consciousness called the Samadhi, which is beyond the deep sleep state in terms of metabolism.
Practice of yoga brings about changes such as slowing of the breath, calming of the mind and relaxation of the body leading to efficiency/balance or homeostasis. [9] The earliest study on metabolism by Anand et al.[13] has demonstrated that a yogi could reduce oxygen consumption while sealed in an airtight box for nearly ten hours, thus changing metabolism at will. Studies on meditation have demonstrated that Transcendental meditation (TM),[5,6] Zen Meditation,[8] Om Meditation, and Yogic Relaxation[14] reduce oxygen consumption, respiratory and heart rates and spontaneous Galvanic Skin Response (GSR).[15,16] The above changes are attributed mainly to reduced sympathetic activity / arousal response and decreased mental and muscular activities.

Studies done on a certain type of Pranayama (breathing technique) called UJJAYI demonstrated a 19% increase in oxygen consumption.[17] Right nostril breathing increased oxygen consumption by 28%.[18] Practice of Asanas or specific postures also increased oxygen consumption.[19,20] All these
changes have been seen as the immediate acute effect of yoga practices. There is no literature report as to how long these changes last or the influence these practices have on the diurnal metabolic rates measured at two different times of the day in experienced yoga practitioners.
A typical yoga capsule usually consists of Asana, Pranayama and deep relaxation or meditation, which has a combined effect but ultimately leads to deep relaxation and reduced oxygen consumption.[4] It is believed that all these must have some permanent effect on metabolism when practised over a period of time, leading to efficiency and relief from stress, thereby resulting in certain changes in the diurnal metabolism, BMR and sleep. Wallace et al. have reported the effect of acute practices resulting in the reduction in metabolic rate in meditation as compared to sleep.[5,6] The present study examines whether there is also a long-term effect of the combined practices.
With this background, the present study was conducted to know: (1) Is there any difference in the diurnal metabolic rate at two different times of the day (6 a.m. and 9 p.m.) of trained yoga subjects compared to those in the non- yoga group? (2) To compare the metabolic rate at 6 a.m. with that of the subjects’ BMR values predicted by the 1985 Food and Agricultural Organization/World Health Organization/United Nations University (FAO/WHO/UNU)
equations.[21]