The Science of Yoga and Why It Works
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The stretches and contortions integral to the ancient Eastern practice of yoga were designed to blend body and soul, meshing the physical with the mental and spiritual. Modern-day science confirms that the practice also has tangible physical benefits to overall health benefits that can include improved brain function and denser bones.

According to the American Council on Exercise, more than 11 million Americans practice yoga and find that the poses (called asanas) and chants strengthen their bodies, center their minds and help them relax.

There are several types of yoga, but the physical benefits are similar regardless of the type practiced, experts say.

Stretches that soothe

Several recent studies drive home yoga's positive effects on the brain, central nervous system and immune system, said Dr. Loren Fishman, a New York City physician who is also a yoga instructor.

"It thickens the layers of the cerebral cortex, the part of the brain associated with higher learning, and increases neuroplasticity, which helps us learn new things and change the way we do things," said Fishman. He has used yoga in his medical practice to treat myriad conditions, including multiple sclerosis , carpal tunnel syndrome, arthritis and rotator cuff syndrome, he said.

Other research indicates long-term yoga participants significantly gain bone density over two years' time, which Fishman attributes to the effects of muscles working against gravity.

"Yoga pits one group of muscles against another, exerting many times the force of gravity," he said. "That increases the stress on the bones, and the bones react to that by thickening."

Types of yoga

"Relaxation is when the body and mind are in a state of balance," said Jasmine Kaloudis, a yoga instructor in Philadelphia. "It means releasing chronic muscle tension ... restoring natural diaphragmatic breathing, and improving oxygen absorption. The postures have many tangible physical benefits for every major system of the body."

Each type of yoga has a slightly different focus, and one may be more appropriate than another for people who have certain interests and abilities. According to American Council on Exercise spokeswoman Elizabeth Larkham, who is a yoga instructor in San Francisco, these types include:

  • Ashtenga: The oldest form of yoga, Ashtenga is also known as "power yoga" because it is fast-paced and rigorous.

"It would be considered the most athletic," Larkham said. Because of this, students sometimes are injured doing poses beyond their range of flexibility.

  • Vinyasa: Focus is on how breathing affects the mind and body, Vinyasa is based on a series of poses called the sun salutations, in which movement is matched to the breath. While rigorous, the postures flow together smoothly.
  • Iyengar: This practice usually emphasizes holding poses over long periods, which is good for those with injuries or chronic illnesses who want to become more flexible.

"It can be exceptionally beneficial for someone with a musculoskeletal injury," Larkham said. "It helps refine the body's alignment."

  • Kundalini: Combining rapid, repetitive movements rather than drawn-out poses, Kundalini includes chanting throughout the session. Participants focus on exploring the effects of breathing on their postures.
  • Bikram: Also called "hot yoga" because it's done in rooms where the temperature is at least 90 degrees Fahrenheit (32 degrees Celsius), Bikram "is very acceptable to people in the West, because it omits headstands and handstands," Larkham said. "The heat makes the soft tissues in the body more pliable, so it's easier to do poses."

Practicing Bikram, however, may be dangerous for those with high blood pressure, a heart condition, diabetes or another chronic illness , according to the Cleveland Clinic.

Larkham and Kaloudis said each of the three categories of movements incorporated into most yoga types standing poses, inversions, and back and forward bends stimulates different bodily systems.

For example, standing poses strengthen leg muscles, open the hips and flex the back, improving circulation to the lower extremities, Larkham said.

Upside-down poses such as headstands, called inversions, increase blood flow to the heart, lungs and brain. They also "stimulate lymph to move toxins out of the body, which is beneficial for the lymphatic system," Kaloudis said.

Back bends make the spine more flexible, and stimulate the central nervous system, and could help people deal with negative emotions, Larkham said.

Forward bends are "calming and restorative for exhaustion and blood pressure," Larkham said.