Physiology of Yoga

“Just take a deep breath.” This is likely an instruction you have heard whether you practice yoga regularly or have never set foot inside a studio. Almost intuitively, we know that stopping and taking a long, deep breath can help calm our body when we are feeling overwhelmed, anxious, or frustrated. Indeed, a host of research articles support the physiological benefits of  slow, deep breath. The breath can be maneuvered in many other ways to produce different physiological effects. The practice of controlling the breath, whether it be the rate, depth, or entry/exit point, is an ancient practice known as pranayama and stands alone as the fourth limb of yoga in The Yoga Sutras of Patanjali. There are countless modes of breath manipulation—each of which initiates a physiological event—that can lead to calming, energizing, heating, cooling, and cleansing effects, among others. By employing different styles of pranayama, we have the ability to influence several physiological systems, including cardiovascular, nervous, respiratory, digestive, and musculoskeletal.

The most basic form of pranayama is an equal, counted breath known as sama vritti pranayama. This yogic practice is equivalent to the slow, deep breathing techniques described in medical and scientific research on breathing techniques. To practice this breath, come to a comfortable seat and begin inhaling for a specified count, then exhale for an equal amount of time. The inhales and exhales can gradually be lengthened, stopping at the point when breathing becomes strained or is no longer comfortable for the practitioner. The most obvious benefit of this type of breathing is strengthening the accessory breathing muscles, such as the internal and external intercostals (located between the ribs). Since we are actively concentrating on inhaling for longer than normal, we utilize more of our lung capacity. The average person only utilizes about one-third of their total lung capacity in normal, uncontrolled breathing. When we actively manipulate our inhales and exhales, we strengthen the muscles and prepare ourselves for situations when the breath needs to be increased (like exercise).

Several other benefits of this type of breathing have been widely documented and include decreased blood pressure, improved tone in the autonomic nervous system, decreased anxiety, and improved digestion. But how exactly does a lengthened breath translate to changes across such a broad scale? The basic answer is that by guiding the breath in such a manner, we initiate a cascade of events that lead to up regulation of the parasympathetic nervous system (the “rest and digest” response) and a down regulation of the sympathetic nervous system (the “fight or flight” response).

The cascade begins with stretch receptors in the lungs, aortic arch (the blood vessel directly exiting the heart), and carotid arteries (blood vessels along the throat). Inside the lungs, an increase in the tidal volume (the amount of air inhaled) will activate the Hering-Breuer reflex. This reflex translates the increased activity of the stretch receptors to increased activity of the vagus nerve. The vagus nerve can be thought of as the main highway of the parasympathetic nervous system, as its branches exert influence over the heart, blood vessels, and many other organs. The net result is an increase in the release of “relaxing” hormones and a decrease in the release of “excitatory” hormones. A similar reflex also happens with baro-receptors in the aorta and carotid bodies in the carotid arteries; an increased stretch and volume of oxygen in the blood triggers a reflex that results in increased vagal nerve tone and, therefore, increased release of “relaxation” hormones. When the body is flooded with these relaxation hormones (such as GABA), the heart rate slows, blood vessels relax (resulting in decreased blood pressure), anxiety decreases, and digestion improves.

Another basic form of pranayama—and probably the most familiar to yogis—is ujjayi breathing. Ujjayi breath is similar to the slow, deep breathing techniques mentioned above, but it adds a slight constriction at the back of the throat on the exhale, and requires the mouth to remain closed, forcing the nose to be the exit point for the breath. These extra elements provide the added component of heating the body, since heat does not escape the body as readily from the nose as it does from the mouth. This can be very useful in yoga practice, as we aim to build heat inside the body, but it can also be employed in everyday life when the body is in need of a temperature boost (cold, Boston winters, anyone?). While some might argue that the constriction at the back of the throat (initiated by the contraction of the glottis muscles) might provide an additional increase in pressure in the neck, there is not yet any scientific evidence to support this claim. Therefore, ujjayi breath does not necessarily increase vagal responses and parasympathetic reflexes above the response initiated from sama vritti pranayama.

Our breath has the potential to play a far greater role in our well being than simply delivering oxygen to the body. With even with the most simple manipulation, we can strengthen our musculature and positively affect organs and tissues throughout our entire body, thus altering our psychological and physiological states for the better. By incorporating elements found in ujjayi breathing to our daily lives, we can heat the body, helping to prepare it for exercise or to combat the elements. Bear in mind that these are just two of the most simple and common pranayama practices; there are many others that can be utilized to produce profound systemic effects. In upcoming posts, the physiological impact of more advanced pranayama practices will be explored, allowing us to dive deeper and fully uncork the power of the breath.