It is an unpleasant historical irony that the cliché about the supposed weakness of Jewish men had two main proponents with diametrically opposed agendas. European anti-Semites opposed to citizenship for Jews claimed that these “degenerates” couldn’t serve in their nation’s armed forces. Then a faction within Zionism used virtually the same rhetoric to vilify the diaspora and the victims of the Shoah.

“The Mighty Atom,” a charming, if somewhat baggy, new documentary, available digitally, as of Nov. 14, offers an unlikely but dramatic refutation of this libel.

The film tells the story of Joseph Greenstein, a Polish-born Jew who grew from a sickly child with tuberculosis, supposedly doomed to an early death, into “one of the greatest strongmen to ever live,” as one of the film’s many interviewees puts it. The adolescent Greenstein, whose father had already died from the disease, was told he wouldn’t live past 18.

Then the circus came to town, literally.

The Greenstein boys, from left, Henry, Isaac, Mike, Jerome and Joseph, the Mighty Atom. Courtesy of SDG Films

After a series of mishaps, the young Greenstein was befriended, virtually adopted, by a strongman who was, not coincidentally, Jewish. The boy ran off with the troupe and traveled the world, gradually building himself up while acquiring knowledge of martial arts, secrets of strength and mind control that would serve him for the rest of his life. By the time he emigrated to the U.S., settling in Galveston, Texas, Greenstein was an impressive specimen of muscle and sinew, although only 5-feet-4 and 140 pounds.

Fate altered his life and career when a customer needed a flat tire fixed and stumbled into the gas station Greenstein owned. He trotted down the road to help out, startling the passengers in the back seat by lifting the car one-handed, while stripping off the flat and putting on the spare with his free hand. One of the occupants of the suddenly elevated back seat was Harry Houdini. Greenstein abruptly departed the gasoline business and Galveston.

Brought to New York by Houdini’s manager and billed as The Mighty Atom, he worked up an act that he would perform for decades, first in vaudeville, then at county fairs, on television and in theaters across the country and around the world. His repertoire ranged from pulling a string of cars along the street with his hair to biting through six-penny nails and bending horseshoes. He did all this while wearing a singlet with a Magen David prominently displayed on its shoulder strap. And when his several sons became old enough, they joined the act.

The 1920s have been called “the era of wonderful nonsense,” and acts like Greenstein’s epitomize the harmless, somewhat goofy nature of the period’s entertainment. But in the 1930s, the Atom’s feats of strength took on a more serious character as he battled the German-American Bund and other Nazi-sympathizing hecklers. The film recounts instances of the diminutive Greenstein manhandling groups of larger men, occasionally using a Hank Greenberg-model baseball bat as an equalizer.

Greenstein’s repertoire ranged from pulling a string of cars along the street with his hair to biting through six-penny nails and bending horseshoes, all while wearing a singlet with a Magen David prominently displayed on its shoulder strap.

Throughout his time in the public eye, which lasted until he was well into his 80s (or possibly younger, since he had a penchant for exaggerating his age in the media), Greenstein used his act as a platform for lecturing on proper eating habits, good health, exercise and the power of the mind to control the body. He would caution audiences, “You dig your grave with a knife and fork.” (Greenstein died in 1977.)

He created a line of soaps, laxatives and skin-care products that he would peddle at the conclusion of his demonstrations. (Given that he had a luxuriant head of hair up to his death, and used it to do things like stopping a plane from taking off, a line of hair-care products might have been even more popular.) He left behind an impressively dedicated generation of acolytes that included not only his sons — and grandson Steve Greenstein, who made the film — but also some of the most heralded strong-man acts of the post-WWII era who, in turn, carried on his traditions.

The Mighty Atom pulls a firetruck with his hair in front of a crowd in New Jersey. Courtesy of SDG Films

Much of the film consists of the reminiscences of the Atom’s surviving sons and his followers, although the chief researcher for “Ripley’s Believe It or Not” is an appropriate and enthusiastic witness. More convincing still is the testimony from several professors and researchers in biomechanics. But the best part of the film consists of interview and performance footage of its hero.

The only real drawback to “The Mighty Atom” is that it is a bit shapeless. The timeframe of Greenstein’s life is frequently unclear. There are long digressions into such tangentially related matters as a young woman who saved her father’s life by lifting a car off his chest, and the gym/art studio of a man who makes sculptures out of the steel objects he bends with his hands. At times the film threatens to turn into a shaggy dog story (albeit one in which the dog could drag a truck with its fur), but Steven eventually returns to his grandfather’s feats of strength, both physical and mental. As a result, despite its digressive nature, “The Mighty Atom” is good fun and a splendid rebuttal to the myth of the weakling diaspora Jew.

“The Mighty Atom,” directed by Steven Greenstein, is available on iTunes, Amazon and Google Play.