The Science of Yoga: The Risks and the Rewards

by William J Broad

  As Paul suggested, many aspects of yoga reinforce slow breathing and limit the exhalation of carbon dioxide, including the repetition of mantras and chants. In 2001, Luciano Bernardi, a medical internist at the University of Pavia, in Italy, reported on a study of nearly two dozen adults. His team found that the repetition of a mantra cut the normal rate of respiration by about half, reinforcing mental calm and producing an enhanced sense of well-being.

  In short, science over the decades has learned a lot about how yoga breathing affects a person’s mood and underlying metabolic state. Fast styles tend to excite and slow ones to calm.

  And it has nothing to do with getting more or less oxygen into the practitioner’s body, contrary to innumerable yogis and gurus, video discs and yoga books, blogs and newsletters. Nevertheless, some yoga authorities go so far as to issue delusional warnings.

  “You’re not used to so much oxygen pouring into your system!” Choudhury, the guru of hot yoga, cautions students who do his deep breathing and begin to feel dizzy. He says nothing of big carbon dioxide drops, the real cause of blackouts.

  The blunders go on and on. Breath of Fire “increases oxygen delivery to the brain,” said Kundalini Yoga, richly illustrated and highly accessible to beginners. Actually, as we just saw, it does the exact opposite, dramatically so.

  The Complete Idiot’s Guide to Yoga praises the discipline’s breathing as “one of the best things you can do to keep your body filled with oxygen.” The advertised effects sounded a lot like the calm serenity that high carbon dioxide levels can induce.

  The confusion about yoga breathing as a way to fill the body and brain with oxygen goes far beyond simple misstatements and their dissemination through countless books, articles, and videos. Of late, it has spread to a whole new style of the discipline. Oxygen Yoga promotes itself as beneficial “for anyone in need of more oxygen.” Its authors have a line of books. The newest—Oxygen Yoga: A Spa Universe, published in 2010—recommends that health resorts adopt the style for “added revenue.”

  It is said that every disaster has a silver lining. In a similar way, the failure of yoga investigators to find miracle workers who could stop their hearts and live without air led to a major advance in understanding the brain. And that discovery in turn revealed one of the most important ways that yoga can sway emotion. It happened in the decades after Behanan did his experiments, from roughly the 1940s to 1970s.

  The lesser discoveries ended up revising a major tenet of the medical world—that the human body has two nervous systems that are entirely distinct. The newer one starts in the outer brain and radiates out in the nerves that let us move our skeletal muscles and go about our daily lives. The older one begins in the lower brain and regulates the internal muscles, the organs, the instincts, and other primal functions. It is called the autonomic nervous system.

  The medical credo of the day held that its activities were automatic and, with notable exceptions (such as breathing), beyond the control of the conscious mind. But scientists who studied gifted yogis kept documenting abilities that contradicted this tidy picture. In study after study, they found that yogis could seize control of autonomic functions and make dramatic changes of body activity. The automatic system, it turned out, contained options for all kinds of manual overrides.

  One of the scientists was Thérése Brosse, a French cardiologist who examined Krishnamacharya. She and her colleagues wrote extensively on how advanced yogis could unwind in surprising ways, slowing the heart rate and blood flow. Another was Bagchi. Despite his campaign to expose yogic miracles as false, he documented wide yogic control over autonomic functions once considered beyond reach. A 1957 paper of his found “an extreme slowing” of such fundamentals as respiration and heart rate. He concluded that overall, yoga brings about “deep relaxation of the autonomic nervous system.”

  The star of autonomic control was an Indian yogi named Swami Rama. Among other things, laboratory studies showed that he could use his mind alone to change the temperature of his hand, creating a gap of up to eleven degrees across his palm.

  The autonomic system is bifurcated, and the studies showed that advanced yogis could seize control of either side. The sympathetic side promotes the body’s fight-or-flight response, inhibiting digestion and moving blood to the muscles for quick action. It does so partly by telling the adrenal glands to squirt out adrenaline, a natural stimulant that speeds up body functions. Early biologists called it “sympathetic” because they saw its functions as acting in concert or sympathy with one another—all at once. The other side is known as the parasympathetic. It governs the body’s rest-and-digest functions, calming the nerves, promoting the absorption of food, and curbing the flow of adrenaline.

  The sympathetic system is the body’s accelerator, and the parasympathetic the brake. Working together, the two manage the body’s overall energy flow, one preparing for its expenditure, the other for its conservation. For instance, the sympathetic system raises the heart rate, and the parasympathetic slows it down.

  The two also wield control over human moods and emotions rooted in primal energy states—the ups and the downs, the exhilarations of Iyengar and the quietudes of Behanan. The inner states resonate with some of the most fundamental of all human emotions—whether individuals feel safe and protected or threatened and endangered. They reflect not only our survival instincts but the mood swings of childhood.

  The investigations showed that yogis had a special talent for applying the brake. Their adroit slowing of the metabolism and related functions was especially impressive in that it overcame a strong evolutionary bias. The demands of survival mean that the body, left to its own devices, always favors the accelerator. After all, the sympathetic nervous system is essentially a means of emergency response and easily aroused, keeping the body ready for battle or retreat, awash in adrenaline.

  Yogis have pressed these pedals for ages. But recently, a new breed of practitioner has arisen who can not only work the pedals but draw on a wealth of contemporary science to explain the process and how it relates to the experiences of regular practitioners.

  I speak of Mel Robin.

  Many yoga teachers have a reverential aura. Not Robin, not on a rainy Saturday in Pennsylvania as he strode into a crowded yoga studio, his manner relaxed, his beard trim. New Age music played softly in the background.

  “My name is Mel and I wrote this music,” he quipped, getting a laugh.

  Someone asked if he performed it, too.

  “Don’t get smart,” he replied. And with that, Robin shattered the usual atmosphere.

  The Yoga Loft of Bethlehem sat atop an old brick building that seemed to date from the city’s steel days. It had bare wooden floors and large windows. The studio had put aside its regular Saturday classes for a special program featuring Robin on “The Science of Inversions”—poses in which the feet or torso go above the head. The ads suggested that students bring along a copy of his Physiological Handbook for Teachers of Yogasana or buy one at the studio’s shop.

  Women in their thirties tended to dominate the room. Several were yoga instructors, as the class was advanced. Robin was seventy-three and, in typical yoga style, failed to look or act his age.

  He sat on the bare wooden floor, stretching and talking, and over the next three hours took us through some of the nuances of autonomic control. His focus that day was not the kind of mental gymnastics that Rama had displayed. Rather, it was explaining how normal poses can result in autonomic shifts.

  Headstands, he said, tend to excite the fight-or-flight response, especially in nervous beginners. By contrast, he added, the Shoulder Stand pressed the parasympathetic brake, soothing the spirit and making it “one of the most relaxing postures in yoga.”

  We paired off and Robin, a teacher in the Iyengar style, toured the room helping twosomes do Shoulder Stands. When he got to me, I asked if more was known about the reasons for the relaxation.

  Robin said the pose calmed because it seized control of
one of the most important functions of the autonomic system—the regulation of blood pressure.

  It is well known that good health depends on the pressure staying in a narrow range. If it drops too low, the brain gets insufficient blood and we get dizzy, weak, and faint. In extreme cases, organs can fail, producing such breakdowns as cardiac arrest. High blood pressure has its own hazards, though long-term rather than immediate. It stresses the heart and arterial walls, producing hypertension. This is a risk factor for stroke, heart attack, and kidney failure. Because of such dangers, the human body over the ages has evolved a striking array of sensors and defense mechanisms that constantly take pressure readings of the blood vessels and make suitable adjustments.

  Robin said the Shoulder Stand tweaked one particular kind of sensor. It lay in the carotids—the major arteries that run through the front of the neck carrying blood to the brain. The carotid sensors make sure the brain gets the right amount of blood and, given the brain’s importance, get serious attention. Sensors embedded in the arterial walls monitor bulging or contracting that indicate changes in blood pressure.

  Shoulder Stand, Sarvangasana

  But in the Shoulder Stand, Robin said, the chin presses deeply into the neck and upper chest, clamping down on the carotids and making the local pressure very high. That rings alarm bells and the parasympathetic brake flies into action. It assumes that the delicate tissues of the brain are reeling from too much blood and orders the heart and the circulatory system to compensate with pressure cuts. The main response signals go through the vagus—the large nerve that starts in the brain stem and wanders among the lungs, heart, stomach, and other abdominal organs.

  Robin clapped his hands to illustrate the urgent nature of the parasympathetic commands.

  “Don’t pump so often. Don’t pump so hard. Open the diameters. Vasodilate”—the term for vessel relaxation that allows blood to flow at a more leisurely pace.

  I thanked him. Gune may have recommended the Shoulder Stand to Gandhi for its calming effects, but he had nothing on Robin in explaining how it worked.

  Robin volunteered that the scientific approach to understanding the poses made some yogis uncomfortable.

  “There are people who say, ‘You’ve crossed the line. That’s not yoga. Look at Patanjali. There’s nothing about the workings of the sympathetic nervous system.’

  “They are very, very traditional people,” he continued. “My own feeling is—I agree. It’s not yoga. It’s about yoga and understanding it, and that lets you do better yoga.”

  And with that, Robin turned his attention to other students.

  Better yoga. The phrase echoed in my head. A few days later, I called Yoga Loft and signed up for a series of four courses that Robin planned to teach on the science of yoga. The last focused entirely on the autonomic nervous system.

  Right off, he cast the topic in a new light. Most portrayals stress psychological factors—such as existential threats that prompt the fight-or-flight response, or peaceful interludes that bring about rest-and-digest states of contentment. But Robin said the systems could be stimulated not only by environmental factors but from the bottom up by conscious actions. An example, he said, centered on the muscles.

  “If you’re frightened, your muscles get tense,” he said. “But if you do muscle work, that also excites the sympathetic nervous system.” It was a fascinating observation that had all kinds of implications for life and explaining the influence of yoga postures.

  Robin pointed to a place in his book that listed which parts of the body came under autonomic control. The table, spread over four pages, described more than one hundred functions— everything from sleep and gastric secretions to vasoconstriction and shivering. Each entry was followed by a reference number, or several reference numbers, that pointed to the book’s end section of scientific reports. The table seemed to represent a labor of love that summarized decades of research.

  Robin had us turn to another page that listed nine unusually potent effects of sympathetic stimulation. They include a quicker heartbeat (to prepare for action), dilated pupils (to admit more light for better attention to potential threats), and changed blood chemistry (to stimulate clotting in case of bleeding). Most people have no conscious control over such autonomic responses. But two items on the list stood out as relatively easy to influence—muscle tone and respiration rate. Robin called them keys to the hidden world of autonomic control.

  We practiced poses that worked the muscles, seeking to excite the sympathetic nerves. “Any kind of exercise, any kind of muscular work” will do it, Robin told us. He added that the same held true for respiration. “Anything you do to speed up your breath will speed up most parts of the sympathetic system.”

  It was a fascinating idea. His activity rule, given the list of autonomic functions we had just looked at, suggested that a disciplined individual could gain leverage over dozens of the body’s most important and inconspicuous functions. His rule also suggested that different Hatha styles had very different autonomic effects. For instance, Ashtanga, with its fast, flowing movements and its emphasis on Sun Salutations, works the muscles a lot and would thus stimulate the sympathetic system. In contrast, Iyengar, with its emphasis on static poses, would seem to lend itself to parasympathetic dominance.

  Robin expanded the activity explanation a step further and showed us subtle ways in which a pose could engage the parasympathetic brake. His ideas were an elaboration on what he had told me during the inversions class.

  He focused on the heart itself. Robin noted that the right atrium—the upper chamber that gets blood from the veins—bears a sensor that gauges its fullness. When pressure is low, he said, the sensor signals the heart to beat faster, increasing the blood flow. When pressure is high, the heart slows down.

  Robin said inversions worked beautifully—as with carotid pressure—to fool the heart into slowing. It happened because upending the body dramatically increased the flow to the right atrium. Normally, gravity helped a little between the head and the heart. But turning the body upside down let gravity work over a much larger area, strengthening venous flow from the feet, legs, and torso.

  “It’s all downhill,” Robin noted. “So the heart overfills.”

  The rising pressure in the right atrium then signaled the heart to beat slower. That signal, Robin noted, also caused the heart to reduce the strength of its contractions. It was a one-two punch. Overall, the atrial mechanism showed yet another way in which yoga could work inconspicuously to reset the metabolism.

  Robin had us do a heart test. First, we monitored our pulses, measuring their rate against the sweep of a watch. Then he had us move to a wall, lie on our backs, and raise our legs in a relaxed state of partial inversion. Once again, we measured. He noted that the beat was probably slower (which I found to be the case).

  A good yoga practice, Robin said toward the end of class, involved poses that cycled through the accelerator and the brake so the autonomic system got a thorough workout. Robin said the resulting realization of energetic flexibility over the usual conditions of metabolic life resulted in new abilities to achieve states of inner balance and harmony.

  “A large part of the benefits,” he said, “results from going through a couple of cycles every time we practice.”

  The clues gathered over the decades about yoga’s repercussions for human emotion first began to come together in a significant way at Harvard. Herbert Benson was a physician eager to ease Western tension with regular doses of Eastern calming. He and his colleagues studied the issue at the university’s medical school, examining the effects of meditation, yoga, and other soothing practices. Benson called his insight The Relaxation Response. His book, published in 1975, sold more than four million copies and became a modern classic on undoing stress.

  Benson found that simple techniques could have dramatic repercus- sions on his subjects, cutting their heart rate, respiratory rate, oxygen consumption, and blood pressure (if elevated to begin with). Ove
rall, he and his colleagues showed that relaxed practitioners entered a state known as hypometabolism—a wakeful cousin of sleep that exhibits low energy expenditures. He called the relaxation response “an inducible physiologic state of quietude” that healed and revitalized.

  After Benson, many scientists sought to expand his findings and zero in on particular disciplines, including yoga.

  Mayasandra S. Chaya was an Indian physiologist in Bangalore who had practiced yoga since she was ten. Chaya led a team that studied more than one hundred men and women. The scientists prescribed a diverse Hatha routine sure to press both the metabolic brake and accelerator. The dozen poses included the Triangle (Trikonasana), the Shoulder Stand (Sarvangasana), the Locust (Shalabhasana), the Cobra (Bhujangasana), the Bow (Dhanurasana), and the Thunderbolt (Vajrasana), as well as fast and slow breathing techniques. At a session’s end, the subjects assumed the Corpse (Savasana) for a period of conscious relaxation. The men and women—their average age thirty-three—followed the prescribed routine for at least a half year.

  The scientists assessed how the routine affected the basal metabolic rate—the energy spent on the body’s housekeeping functions. In a standard method, they measured the flow of respiratory gases—oxygen and carbon dioxide—as a way of gauging how bright the inner fires were burning, as measured in calories.

  In 2006, Chaya and her team reported that regular yoga practice cut the basal metabolic rate by an average of 13 percent. The results were even more pronounced when broken down by sex. The men on average cut their resting energy by 8 percent. But the women achieved reductions of 18 percent—more than double the metabolic declines of their male counterparts.

  It bespoke the wisdom of Robin’s comments about autonomic cycles. The ups and downs worked to increase not only outer flexibility but inner suppleness as well, giving body and mind the freedom to sink into Benson’s kind of quietude—to just be. It was a secret of letting go.