The Science of Breath

In his book Light on Pranayama, B. K. S. Iyengar writes: “Prana is the breath of life of all beings in the universe.” It’s no surprise, then, that pranayama, or the regulation of breath, is an essential part of yoga practice. In fact, it’s unusual to enter into a yoga class that doesn’t have at least some focus on breathing. As Kripalu Yoga teacher Richard Faulds (Shobhan) says, “Unless practiced with sensitivity to the breath, yoga postures fall far short of their potential to foster healing and growth.”

Numerous yoga texts highlight the importance of breathing practices in regulating the nervous system and, ultimately, in promoting optimal well-being. Experienced yogis know that different pranayama practices produce specific effects: Some techniques are meant to increase one’s energy; other’s to quiet it. Some boost metabolism; others decrease it. While traditionally meant for spiritual development, modern use of pranayama—such as in conjunction with asana practice—is often employed therapeutically to increase both physical and mental health.

As you develop your own pranayama practice or, for teachers, as you continue to offer it to students, it can be useful to pair the yogic understanding of this ancient practice with findings from modern science. Does science complement yoga? To answer this query we look at three commonly practiced pranayamas: nadi shodhana, kapalabhati, and bhastrika. While only preliminary research has been conducted on these practices, findings may both surprise and encourage you to get onto your mat and breathe.

Nadi Shodhana

Nadi Shodhana, or Alternate-Nostril breath, is touted for its ability to reduce stress and still the mind. This practice consists of sitting quietly and breathing into each nostril separately by plugging one nostril and breathing in the opposite nostril. The instruction is to practice going back and forth between each nostril slowly and rhythmically. The practitioner plugs the left nostril, breathes in through the right; plugs the right nostril, exhales through the left. Then he or she repeats this on the other side: Plug the right nostril, breathe in through the left, and onward. Some of the yogic benefits of this practice include calming the mind and reducing stress, releasing tension from the chest and abdomen, and balancing the flow of prana in the nadis (energy channels).

While scientists have yet to find a way to measure changes in energy channels, they are beginning to measure the impact of nadi shodhana on overall physiology. Preliminary studies show that Nadi Shodhana decreases blood pressure, increases skin conductance (which is a marker of sympathetic activity), and increases heart rate.

Interestingly, as many yogis have noticed in their own practice, breathing through one nostril compared to the other produces different effects on the body. For example, in the same study researchers found that breathing exclusively in and out of the left nostril decreases blood pressure, whereas breathing exclusively through the right nostril increases blood pressure. This aligns with the yogic view that breathing into the left nostril activates the ida, the energy channel associated with rest and relaxation, and that breathing into the right nostril activates the pingala, the energy channel associated with activity and action. Bottom line? Nadi Shodhana helps balance the nervous system, evening out differences in sympathetic and parasympathetic tone (i.e., it evens out the fight-or-flight system with the rest-and-digest system) and it also reduces blood pressure, promoting a greater sense of calm and relaxation.


The practice of Kapalabhati, or Skull-Polishing breath, consists of a forceful exhalation and a passive inhalation. In 2009 researchers Meesha Joshi and Shirley Telles published an article on Kapalabhati, in The Journal of Alternative and Complementary Medicine. They wanted to know one thing: Can the practice of Kapalabhati, which can be quite invigorating, improve performance on cognitively challenging tasks? To investigate this query, they ran a study in which they invited participants to practice Kapalabhati at the speed of two exhalations per second, for one minute. Participants were asked to complete a challenging mental task before and after they practiced Kapalabhati. A second group practiced breath awareness in comparison. Results showed that the Kapalabhati group had a significant decrease in the amount of time it took them to complete the task. This suggests that practicing Kapalabhati can improve mental performance. Equally interesting and beneficial, the breath-awareness group showed an increase in neural resources in order to complete the task. This suggests that simply being aware of the breath helps to focus one’s attention.

While researchers are still exploring what contributes to this shift in mental ability, these researchers hypothesize that Kapalabhati provides a gentle stimulation of sympathetic system response, which increases one’s cognitive functioning in such a way that it improves mental performance.

Kapalabhati can be practiced for varying lengths of time, for a short time—as demonstrated in this study—or for longer periods. A word of caution: Kapalabhati can be quite stimulating, so it is best to practice it under the supervision of a trained yoga teacher.


The Bellows breath, or Bhastrika, is another pranayama technique meant to increase energy flow. Bhastrika is practiced by breathing fully and forcefully in and out of the nose. Researchers from the Department of Physiology at Nepal College were curious to see how Bhastrika would impact the nervous system. To investigate this, they invited a group of participants into their lab to practice Bhastrika. The participants were instructed to practice a slow-paced bhastrika: inhaling to maximum for a count of four, then exhaling to maximum to a count of six. At this pace, participants were breathing at a rate of six breaths per minute and they were asked to continue with this practice for five minutes.

What did the researchers find? Bhastrika produced a significant decrease in blood pressure and a slight decrease in heart rate. The researchers concluded that “slow-pace bhastrika pranayama (respiratory rate 6/min) exercise shows a strong tendency of improving or balancing the autonomic nervous system through enhanced activation of the parasympathetic nervous system, and thus can be practiced for mental relaxation and reduction of stress in daily life.” Bhastrika can also increase energy, release tension in the abdomen, and helps loosen congestion and decongest the lymph.

A Pranayama a Day

While all these studies are preliminary, it’s encouraging to see both Western science and the yogic view lining up around the same concept: that certain pranayama practices will lead to certain physiological outcomes. This is a first step in placing solid scientific data quantifying the healing properties of yogic breathing practices. With future studies such as these, the prescription for a “pranayama a day” might get just a little bit closer.

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