The Science of Yoga: The Risks and the Rewards

by William J Broad

  At Kripalu, for three days, Weintraub marshaled every available weapon in the yoga arsenal to teach us how to seize control.

  “You’ll be feeling lighter and brighter or your money back,” she said with a smile. Her methods were not particularly strenuous. But they all took aim with great precision at lifting the spirit. We relaxed. We visualized. We did balancing poses that forced us to shift our attention from mind chatter to the here and now. We laughed. We stretched. We made calming sounds. We did Breath of Joy—inhaling, bringing our arms slowly up to the sky, then exhaling with a breathy “Haaaa” while bringing our arms down rapidly. By the end of it, we glowed, lit from within.

  Weintraub understood the science and told our class about a number of studies and researchers. It turned out that she knew Khalsa and was working with him on one of his investigations—to compare the benefits of yoga with those of psychotherapy. She also had a book in the works: Yoga Skills for Therapists.

  All this may sound new and fresh. But it turns out that Harvard, Boston, and Massachusetts have long played host to individuals and institutions with abiding interests in yoga’s emotional sway. In fact, I suspect that is the core attraction of Kripalu, which has drawn waves of interest for decades and describes itself as the nation’s largest residential center for yoga and holistic health. The facility is located on hundreds of rural acres far from the usual pleasures and distractions of urban life.

  On the Friday that I signed in—with the leaves of the trees gone and the area dappled in white from a recent snowfall—Kripalu succeeded in registering nearly five hundred guests for its weekend classes. The vast majority were women.

  Thoreau characterized yogis as having no earthly care: “Free in this world as the birds in the air.” In 1849, he told a friend that he considered himself a practitioner—the first known instance of a Westerner making that claim. “I would fain practice the yoga faithfully,” Thoreau wrote. “To some extent, and at rare intervals, even I am a yogi.”

  At Harvard, his alma mater, William James looked favorably on yoga as a means of mental regeneration. The famous psychologist, trained as a medical doctor, zeroed in on one of yoga’s most basic exercises—the simple but systematic relaxation of the muscles.

  The pose is called Savasana, from sava, the Sanskrit word for “dead body.” Today we call it the Corpse. It is the easiest of yoga’s positions. Rather than twisting or stretching, students simply lie on their backs, eyes shut, and let their arms, legs, and other body parts go limp. In this state of repose, students relax their muscles as much as possible, entering a condition of deep rest. It is usually done at the end of a yoga class and seems to have been around for centuries.

  Corpse, Savasana

  James, in his 1902 book, The Varieties of Religious Experience, identified that kind of letting go as “regeneration by relaxation” and suggested that it could not only revitalize the spirit but advance the more ambitious goal of fostering healthy life attitudes. “Relaxation,” he wrote, “should be now the rule.”

  A graduate student paid close attention. His name was Edmund Jacobson. A physiologist, he had come from Chicago to work on a doctoral degree at Harvard. The gospel of relaxation caught his eye and, following the lead of James and other professors, he threw himself into an experimental study. It focused on the startle reaction—in particular to how subjects reacted when a strip of wood was slapped down on a desk with a sudden crack. To his surprise, Jacobson found that relaxed subjects had no obvious reaction. He surmised that deep relaxation caused mental activity to drop.

  Jacobson tried relaxation himself. Like many students, he suffered bouts of insomnia. But in 1908 he taught himself how to relax and found that the lessening of muscular tension let him enjoy a good night’s rest.

  Jacobson became a convert. Upon taking a job at the University of Chicago, he pursued an ambitious agenda of research and treatment, more or less founding the medical field of trained relaxation. His books included Progressive Relaxation (1929) and You Must Relax (1934), which went through more than a dozen printings and editions.

  Jacobson would have patients close their eyes and tense and relax a body part, concentrating on the contrast. In time, they would get the hang of reducing the tension. Jacobson claimed that his method produced remarkable cures, eliminating everything from headaches and insomnia to stuttering and depression.

  To satisfy his own curiosity—and to convince skeptics of the method’s importance—Jacobson worked hard to gather a body of objective evidence. His goal was to develop a machine that would let him track tiny electrical signals in the muscles and measure subtle currents of a millionth of a volt or less. In his efforts, Jacobson got considerable aid from Bell Telephone Laboratories—then the world’s premier organization for industrial research, which in time won a half-dozen Nobel Prizes. The collaboration between medical doctor and industrial giant resulted in innovations that foreshadowed the electromyograph, a medical instrument that records the electrical waves of skeletal muscles.

  Jacobson made what are regarded as the world’s first accurate measurements of tonus—the normal state of slight muscular tension that aids posture and readies the body for action. The instruments showed that his methods could induce deep calm.

  One patient was a woman who suffered a skull fracture when she got caught in a folding bed. For years afterward, she complained of a nervous condition that made her overly emotional. When Jacobson hooked her up to his apparatus, he found that her muscles did in fact exhibit electrical spikes even when she tried to remain as calm and tranquil as possible. Later, after the woman learned to relax deeply, the waves vanished. And she found new strength and stability in her emotional life.

  As Jacobson studied one way of letting go, other means of calming the mind and refreshing the spirit came under investigation. One scientist looked at controlled breathing and did so through the lens of one of the most fashionable emerging fields of the day, psychology.

  Kovoor T. Behanan was born and raised in India. In 1923, he graduated from the University of Calcutta with distinction. He traveled to the United States and Yale, first to study religion, then philosophy and psychology. In 1931, he won a fellowship to travel back to India and evaluate the psychology of yoga.

  Behanan did the reasonable thing. He journeyed to the world capital of yoga research—Gune’s ashram in the mountains south of Bombay. There he threw himself into learning yoga under Gune’s personal guidance. From April 1932 to March 1933, Behanan practiced every day, doing postures, breathing exercises, and concentration training. He then returned to Yale determined to do a series of scientific experiments that would explain his newfound joy.

  Behanan started in early 1935, after he had been practicing yoga for more than three years. He studied his own mental reactions, seeing the work as exploratory. In particular, he zeroed in on one of yoga’s easiest kinds of breath control.

  Ujjayi Pranayama is known as Victorious Breath. Despite its intimidating name, the style involves simply breathing in and out with great deliberation, the glottis in the throat slightly contracted so the breath makes a hissing sound, like the soft roar of the ocean. Behanan would inhale slowly through both nostrils. After filling his lungs to the brim, he would hold the breath for the same length of time as the inhalation, and then exhale steadily for the same duration.

  Resting adults breathe anywhere from ten to twenty times a minute. Ujjayi is much slower. Behanan reports that he did the exercise at a rate of twenty-eight cycles in twenty-two minutes, or a little more than one per minute. In other words, he breathed about ten times slower than a resting adult. It was the kind of slowdown that Paul had described in his book A Treatise on the Yoga Philosophy.

  The psychological testing went on for thirty-six days. Behanan would do the evaluations before and after the breathing exercises to see how they changed his state of mind. The tests consisted of adding numbers, breaking codes, identifying colors, doing puzzles, and performing little exercises in physical coordina
tion.

  He published his results in a 1937 book, Yoga: A Scientific Evaluation. He now had a doctorate from Yale, as the title page noted prominently, and the book was well received. Life ran a formal portrait of Behanan in coat and tie and photographs of half-naked students upending themselves in tricky poses. The feature was spread over two pages. Time ran a glowing review. It called him handsome, thirty-five, and a first-class poker player.

  Behanan’s central finding turned out to be a lucid confirmation of Jacobson’s surmise about deep relaxation causing a drop in mental activity. Across the board, the breathing exercise brought about what Behanan called “a retardation of mental functions.” The finding, he conceded, might leave readers a little surprised.

  All the tests took him longer to complete, up to twenty-six seconds longer. The yoga breathing had its greatest impact—and produced the greatest lag—on his math abilities.

  His findings, Behanan noted, contradicted the popular image of yoga as a magic elixir that endowed its practitioners with superhuman powers. But he hailed the mental slowing as important because of its repercussions for mood. The breathing exercise, Behanan reported, brought about a state of deep relaxation that produced “an extremely pleasant feeling of quietude.” The inner pleasure became even greater if he added concentration exercises. “I would like to prolong it indefinitely,” he wrote of the floating state, “if it were in my power to do so.”

  The evidence indicated that the mental slowing was temporary and Behanan held out the possibility that the period of refreshment might actually produce an overall improvement in “our normal intellectual faculties.”

  At the book’s end, Behanan summarized his own reaction to his newfound discipline. Yoga, he said, had remade him.

  Before, he had frequent headaches, felt run down, and lacked what he called pep. But his days at the ashram gave him new energy and “emotional stability.” Behanan saw the same in his ashram colleagues.

  “They were the happiest personalities that I have known,” he recalled. “Their serenity was contagious.”

  If only he had stopped there. In his book, Behanan went on to describe experiments he had done at Yale in respiratory physiology (a very different field with very different methods and measurement techniques that in many respects are more difficult). He reported that Ujjayi caused a spike in oxygen consumption—more than any other breathing style that he investigated. To all appearances, the oxygen boost seemed to be the secret of yoga serenity.

  But it was only the myth, yet again. Behanan had left India before Gune cast doubt on the popular doctrine of the surges, and the research of the Yale investigator proved to be flawed.

  Unfortunately, his false report added to the unshakable durability of the oxygen myth, which still haunts popular yoga. And his misapprehension neglected what turns out to be one of yoga’s main sources of leverage over the unruly currents of human emotion—the manipulation of the body’s relationship with carbon dioxide, which both Paul and Gune had begun to glimpse.

  Today, after many decades of research, it is fairly easy to distinguish between fact and fiction, despite the complexities of respiratory physiology. The big picture is the best place to start.

  The atmosphere of our planet is 21 percent oxygen. That’s a lot. In comparison, the levels of carbon dioxide are five hundred times smaller. The human body exploits this ocean by means of hemoglobin—the remarkable protein inside our red blood cells that soaks up oxygen like a sponge and carries it from the lungs to the tissues. Typically, the refreshed hemoglobin of a resting person is nearly saturated with oxygen, holding virtually as much as it possibly can. The usual figure for the level of absorption is 97 percent.

  For yoga, the glut of oxygen in the air and the saturation of hemoglobin in the lungs mean that fast or slow breathing does little to change the levels that enter the bloodstream—as Gune found at his ashram and as I found at the University of Wisconsin. The vital gas is available in large quantities no matter what.

  The body’s consumption of oxygen does go up and down. But science demonstrates that it does so in response to changes of muscle activity, metabolism, and heart rate—not breathing styles. As we saw in the last chapter, cardiovascular fitness can raise peak oxygen consumption.

  The story with carbon dioxide in the bloodstream is dramatically different and variable. Consider a person breathing in a relaxed way. Fresh air mixes in the lungs with stale air, creating an inner environment where carbon dioxide levels remain fairly high. This person, in typical fashion, ventilates the lungs so inefficiently that each relaxed inhalation replaces less than 10 percent of the gas.

  Now consider what happens if that individual starts to breath fast. Blasts of fresh air with extraordinarily low concentrations of carbon dioxide (three-hundredths of 1 percent of the atmosphere) rush into the lungs, lowering the inner levels. Nature seeks to equalize the concentrations. So diffusion quickly draws more carbon dioxide out of the bloodstream and into the lungs. The result is that the body’s levels plunge.

  This view is anything but contentious. It is the standard account found in hundreds of medical textbooks as well as official pronouncements of the U.S. Navy. Its responsibilities for thousands of professional divers make it a global authority on human respiration. Fast breathing “lowers body stores of carbon dioxide,” the Navy’s diving manual states, “without significantly increasing oxygen stores.”

  The common name for fast breathing is hyperventilation, and the common danger is passing out. It can also result in dizziness, headaches, light-headedness, slurred speech, and numbness or tingling in the lips, hands, and feet. The drop in carbon dioxide influences mood in many ways. One is through respiratory alkalosis. It heightens the excitability of nerves and muscles—so much so that many circuits short out, producing tingling in the hands and spasms in the muscles.

  Yogis often feel such sensations after doing many rounds of Bhastrika, a fast-breathing exercise known as Breath of Fire or Bellows Breath, after its Sanskrit definition. Bhastrika puts the emphasis on exhalation rather than inhalation, like the bellows of a blacksmith. In Light on Pranayama, Iyengar says the repeated blasts of the exercise create “a feeling of exhilaration.”

  While exhilaration and nerve excitement go up, fast breathing does something else that has critical repercussions for mood, mental outlook, and potentially health—it robs the brain of oxygen.

  The reason is that the surge in carbon dioxide causes blood vessels in the brain to contract, reducing the flow of oxygen and producing lightheadedness and perhaps blurred vision. Other symptoms include dizziness and giddiness. In extreme cases, a person can hallucinate or pass out.

  What this means in plain English—as crazy as it sounds, as counterintuitive as it seems, as contrary to the teachings of popular yoga as it appears—is that fast breathing lowers the flow of oxygen to the brain, and does so dramatically. Scientists have found that it cuts levels roughly in half. That plunge is why people faint.

  The misunderstandings about fast breathing, once stark, have grown more subtle over the years and decades. Yoga authorities who look into the science of respiration now tend to contradict one another on whether it can disrupt the carbon dioxide metabolism and result in harm. Some issue stern warnings about hyperventilation and caution new students to take Bhastrika in small increments so the body can adjust gradually to the challenge. Others argue that fast breathing—if done right, especially with methods they advertise as superior—does nothing to upset the carbon balance.

  The evidence of the classroom suggests that fast breathing can indeed pose a threat. Many a beginning student of yoga has fainted, and even intermediate students can feel dizzy or pass out. The science on the topic is rather limited. It does, however, suggest that advanced students can adapt to the respiratory push or learn to do Bhastrika and other varieties of fast breathing in ways that lessen the dangers.

  In 1983, three scientists in Sweden reported on a study of three highly trained yogis who did “h
igh frequency breathing” for anywhere from thirty minutes to an hour. The scientists began the experiment by fitting the subjects with catheters to ease the sampling of blood. The arterial tap was meant to open a window on how the changing atmosphere of the lungs was affecting the rejuvenation of the blood and the release of carbon dioxide. The scientists took blood samples as the yogis rested—to create a basis for comparison—and after they had performed fast breathing for at least ten minutes.

  The results showed relatively modest drops— 4 percent, 11 percent, and 30 percent. Interestingly, the most experienced of the yogis, a man who taught the other two as well as regular classes in breath control, exhibited the modest decline. His was the decrease of 11 percent rather than 4 percent. That suggested that factors other than proficiency and experience in pranayama could limit the release of carbon dioxide. Overall, the scientists reported that none of the advanced yogis developed symptoms of respiratory alkalosis—the blood disturbance that can result in light-headedness and collapse.

  The overall repercussions for mood and respiratory physiology are radically different if the yoga breathing is slow rather than fast. The process starts with such varieties as Ujjayi—the kind that Behanan did. He was breathing about ten times slower than a resting adult.

  The consequences again center on carbon dioxide—only this time its rise in the bloodstream, not its fall. Modern investigations echo Paul’s studies of more than a century ago. Today, a standard figure is that cutting lung ventilation in half prompts blood levels of carbon dioxide to double. And the ensuing dilation of cerebral blood vessels means the brain now gets more oxygen, not less.

  Slow breathing turns out to have deep mental ramifications, with increases in calm alertness and raw awareness. Behanan called the state “an extremely pleasant feeling of quietude.”

  Scientists who study animal behavior have linked slow breathing to heightened vigilance. When an animal is ready to protect itself, its exhalations slow. Its heart rate tends to fall. The animal carefully assesses its surroundings to see if it can relax or needs to flee or fight.