The happy yogi, B.K.S. Iyengar, keeps chuckling. When he's not, he's jumping up to demonstrate a body honed by seven decades of yoga.

Iyengar, the man credited with popularizing yoga in the West, had tuberculosis as a teenager. Now he is 86 and nimble. One of his pupils, who practices yoga in San Francisco, says the other day Iyengar moved him back several inches by exerting the pressure of a single toe.

Iyengar says his "intelligence" extends beyond his mind, throughout his body. "I can tell you are not aware of your toe, but I am aware of my toe," he says.

Iyengar's face is kind and his gray eyebrows are like bushy wings. Even his eyelashes are gray. He jumps up and shows you a spot behind his knee where a massive knotted ligament protrudes like a tree branch. He is proud of this. He grabs your wrist and pinions it with two spindly fingers that feel like a metal clamp. See? The strength of yoga, he says.

Sometimes he practices five hours a day.

"Sometimes I'm like a madman. I can do from morning till evening. Even, I can forgo food," he says. He laughs.

Iyengar lives in Pune, in the Indian state of Maharashtra, but he is in the Washington area now on the last leg of a tour promoting his latest book, "Light on Life." The book offers revelations from a lifetime of studying yoga, as well as giving some details of Iyengar's own life.

He was born 11th of 13 children in a village about 50 miles from Bangalore. His father, a headmaster, died of appendicitis when Iyengar was about 9, and three of Iyengar's siblings also died. Iyengar himself was born in 1918 during the worldwide influenza epidemic, and his mother, who was afflicted with the disease, passed it on to her infant. The frail child was not given good odds to live, and over the years, he suffered from malaria, typhoid and tuberculosis.

Iyengar says he was always dependent on others to care for him. "It was a parasitic life," he says.

At 14, he moved in with one of his sisters and her husband, who happened to be a yoga teacher and who began teaching Iyengar poses. Iyengar says "destiny forced itself" on him, and for years, he says -- in a description that will no doubt comfort many who've yearned to achieve the quiet strength of a master yogi -- his body and mind struggled with each other, his will power often failing him.

"I was a restless practitioner for years," he says.

Iyengar says a strong mind cannot exist without a strong body, and that for a long time he was mentally weak. He says at 16 he failed an exam that would have allowed him to continue his studies. His 1966 book, the seminal "Light on Yoga," was greatly helped, he says, by an editor who gave him "lots of beatings."

It took decades for people in the West to come around to yoga. In 1956, Iyengar made a trip to the United States. A story in The Washington Post and Times Herald from that visit recounted his demonstrations with an arched eyebrow, dubious that "such body-twisting is good for a person."

John Schumacher, a yoga teacher who hosted Iyengar at his Potomac home yesterday, started teaching in the mid-'70s.

"The only people doing yoga then were retired little old ladies and weirdos and hippies," Schumacher says. "I was one of the latter."

In a program last night dedicated to Iyengar at George Washington University's packed Lisner Auditorium, Schumacher asked the guru how busy people could make time to practice their yoga. Iyengar, a father of six, recalled waking at 3 a.m. to practice and stealing more time while waiting for rice to cook.

What could be more important than health? he asked. Certainly not going to the movies. He encouraged people to practice while waiting for their washing machines to finish.

This is Iyengar's first visit to the country in 12 years. He largely has stopped teaching classes, except he can't help correcting "when these people commit mistakes," he says, gesturing to a group of followers who have gathered at Schumacher's home before his public appearance. These days celebrities like Annette Bening and Ali MacGraw follow Iyengar, whose grandson is accompanying him on this trip. He says he feels like it is time for him to move aside and allow others to become known for their yoga teachings.

"I'm like a banyan tree in the field of yoga," he says. "Nothing grows under that tree."

He has written an upcoming book about yoga for those who play cricket, but as for whether he'll write another major book, he deflects the question. He says he doesn't have any plans to overshadow his current book.

"Even if I know, I'll say no," he says coyly, and laughs, again.

Staff writer Neely Tucker contributed to this report.

B.K.S. Iyengar's 1966 book, "Light on Yoga," helped introduce the practice to America. He is in Washington with a new book on the discipline. Yogi B.K.S. Iyengar, 86, who popularized yoga in the West, at his hosts' home in Potomac for his first visit to the United States in 12 years.