When this year's International Day of Yoga rolls around on Tuesday, there will be plenty of ways for yoga devotees in the U.S. and around the world to celebrate. A survey conducted earlier this year by Yoga Journal and Yoga Alliance found that the number of Americans who practice yoga was up to 36 million, with those people spending a combined $16 billion a year on accessories, classes and other yoga expenses. In addition, 80 million people who had never done yoga said they thought chances were good that they'd give it a shot this year.
That means things have seriously changed since the early 20th century, when the practice first began to creep into the American spiritual and athletic mainstream. But, from LIFE Magazine's very first years in the 1930s, the publication and its photographers were chronicling that growth.
In 1937, the magazine followed the news that a Yale scholar from India had examined the science behind yoga, which was explained to readers as a mystic Hindu practice that let the expert, through muscular control, detach from mind and body to allow the "higher world-soul" to join with him. "Whatever the religious result of yogic exercises may be," the magazine reported, "they undoubtedly have therapeutic value, help general bodily health." A few years later, in the article from which the first slide above is drawn, the magazine profiled the "lithe young devotees of an ancient and honorable religion" whom photographer Wallace Kirkland had met on a trip to India. In the decades that followed, with the help of celebrities like violinist Yehudi Menuhin and participants in the truth-seeking of the 1960s and '70s, the magazine stopped having to explain what yoga meant to readers.
As for the reason behind the practice's popularity, perhaps it all came down to the explanation offered by "yoga guerrilla" profiled in 1970, and pictured above in the 16th slide: "Yoga gets me reconnected," he told LIFE. "As soon as I get into the position it begins to happen for me. The center of the earth becomes located in my stomach, my head is in the stars, and yet I am here too. Yoga really works, which is why I think it will be popular."