The Science of Yoga

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 scienceto 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 knownthat 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 ShoulderStand, 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