The Science of Yoga

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 thathad 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. Whenpressure is low, he said, the sensor signals the heart to beat faster, increasing the blood flow. When pressure is high, the heart slows