Yoshimitsu Yamada has been showing students at the New York Aikikai on West 18th Street in Chelsea how to deflect, throw and pin opponents for 50 years. At 76, he can still toss a full-size man onto his head or incapacitate a charging assailant with any number of joint-twisting techniques.

"As a young boy, I wanted to beat up some guy," Mr. Yamada said, recalling his childhood in postwar Tokyo and the impulses that led him to try the then-burgeoning martial art.

The sensei, an eighth-degree black belt and one of the longest active practitioners, is also one of the last living direct students of aikido's founder, Morihei Ueshiba, a pedigree that makes him a sought-after instructor around the world.

As aikido went global, Mr. Yamada brought the martial art to New York in 1964.

"I spoke a little bit of English, and I like American culture, like jazz and musicals, and American girls," he said. "New York was always my dream. If I ended up in a small town in the South, I wouldn't have lasted 50 years."

The art's core practices of harmonizing with an opponent's force and cultivating one's ki have sustained him when most would have long ago hung up the cotton uniform known as a gi. His dojo has survived in part because the organization bought its building about 20 years ago for $500,000.

As the city has become safer, fewer students want to learn how to defend themselves. And many traditional martial arts have become overshadowed by the popularity of mixed martial arts.

Mr. Yamada instead focuses on helping city dwellers better connect mind with body.

"Those who stay with me, they learn something else, not only the physical side," he said. "Depending on how people take it, they gain some positive thinking, gain some confidence."