The Science of Yoga

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 almamater, 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. Butin 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