Comparative machismo is hardly new, but when Donald Trump publicly admired Senator Jon Husted’s backside earlier this month, later telling advisers it made the since-defeated Ohio incumbent more “interesting” to voters, the senator leaned into the compliment, saying it gave him extra motivation to “get down to the gym”.

Would that odd exchange have taken place without CrossFit, the fitness empire founded by college dropout and gymnast Greg Glassman in the 1990s that grew to 15,000 gyms across 160 countries before he was drawn into public controversy at the height of #MeToo and the social justice movement in 2020?

The question is not directly addressed in The Glass Box, an astonishing new account of Glassman’s spectacular rise and fall and of a fitness movement that encouraged adherents to participate in high-intensity workouts. “Hard Work Pays Off” was the mantra; “Mechanics, Consistency, and then Intensity” was the programming; and “Forging Elite Fitness” was the goal. It was an aesthetic and attitude that even bled into right-wing politics and militarism.

But it did not begin that way. At seminars, CrossFitters were first encouraged toward the Zone Diet (“eat meat and vegetables, nuts and seeds, some fruit, little starch, and no sugar”), and later the paleo diet, also known as the caveman or stone age diet, that imagined what humans would have eaten in the Paleolithic era, all the better for the grunting that accompanied “constantly varied, high-intensity functional movements”, as Glassman put it.

Glassman had polio as a child and had used gymnastics to rebuild his strength. It was until his 30s that he began working as a personal trainer in Santa Cruz, California, and developed a system of weightlifting, gymnastics, and sprint conditioning. He opened his first gym in 1995 and was hired by the police department to train their officers.

Overbooked by demand from private clients, he started group classes and the CrossFit community and empire was born, with Glassman himself attaining guru-like status. He was, by turns, charming and irascible, and prone to bluntness and profanity. He told his wife, Jenai: “This next year I’m going to have a lot more sex, either with or without you.”

He was also accused by former employees and CrossFit athletes in a New York Times exposé of creating a culture of “routine and rampant sexual harassment”.

Glassman denied such conduct. A spokesperson said the negative accounts were “a collective effort to devalue the company and buy it for scraps”. He linked racism and the Black Lives Matter movement to the pandemic, tweeting “It’s FLOYD-19.” He once said on a Zoom call: “I do not mourn George Floyd.”

Stories about profligate spending on private jets, restaurants, alcohol, Mariachi bands and stays at the Four Seasons emerged; Glassman explained he was not the CEO of a publicly traded company caught with his hand in the till.

“The till was mine,” he said. “I owned 100 per cent of the company.”

Calum Marsh, author of The Glass Box and former CrossFit devotee, says the program had been developed as an accessible, “easy, safe way of training, mainly for people who were overweight, senior citizens and the infirm – something that could be done by anyone”.

As it evolved, Marsh says, it became popular with people in the military, the police and first responders. “People in those fields gravitated to it because, at its extreme, it can be very intense. So it became popular as a more rugged, macho version of a typical workout and moved away from its original ethos.”

Alongside that, CrossFit gained a political reputation. The company had been founded shortly before 9/11, and the new workout ethos complemented the era of what Marsh calls a “more self-determined and hardened, battle-ready stance. It was a perfect time for CrossFit to take off.”

Of course, every era finds its complementary physical aesthetic. CrossFit launched a website that could be accessed by military personnel serving in Afghanistan and the Middle East. “CrossFit pursued and cultivated an affinity by naming workouts over fallen service members and plastering its website with images of people in the military, guys jumping out of helicopters and doing pull-ups on the end of a tank.”

The association, though never formalized, stuck, and can still be seen today in Trump administration figures, including defense secretary Pete Hegseth, who made physical fitness a military priority and his own physical training, a centerpiece of his command.

Robert F Kennedy Jr also has prioritized viral fitness challenges and high-intensity workouts that mirror CrossFit, along with displays of his own physique. Hegseth and Kennedy launched the online “Pete and Bobby Challenge” as part of Kennedy’s “Make America Healthy Again” (Maha) platform.

“There’s a big premium paid to being perceived as being manly and rugged, and that totally ties into the early Bush-era, CrossFit style,” Marsh says. The aesthetic of CrossFit gyms cultivated in that era – “no mirrors, no vanity, rough garage-style” – is what they tried to re-assert in the Trump era.

The CrossFit aesthetic arrived in contrast to an early period of fitness culture. TV personality Tony Robbins developed a time-efficient routine that promoted cold water immersion, mental “priming” exercises, rhythmic breathing exercises and a fast 15-minute high-intensity workout.

The message then, according to Marsh, was to be able to get fit without really trying. That, too, had developed out of the 1980’s era of “Jane Fonda’s Workout” and the dawn of the health club – upscale boutique places with soft jazz meant to appeal to suburban moms or businesspeople. Then came the 90s era of the ThighMaster and Buns of Steel.

“Everything about the way they were marketed and positioned was to de-emphasize how difficult they were,” he says. The message of CrossFit was the opposite. “It was unheard of at the time,” Marsh says. “You’re gonna have to try. It’s going to be brutal. You’re going to bleed and vomit.”

Looking back further, Marsh points to 1930s Germany and the body aesthetics of the Nazis captured by Leni Riefenstahl’s Triumph of the Will. That, he concedes, is an extreme example. Physical prowess and the body mirror the culture, and vice versa.

“It’s both responding to changes that are political and helping to shape them,” he points out. “It’s in the air and in the culture and part of what makes these things manifest.”

The book arrives at a time when figures from bodybuilding’s golden age, Arnold Schwarzenegger and Sylvester Stallone, who translated their physiques into movie stardom and have re-emerged as avuncular cultural heroes. Stallone’s recent autobiography The Steps made No 1 on nonfiction book sales charts when it was released last month. Schwarzenegger, too, has been recast as a pro-immigration voice of Republican reason.

In the end, Glassman was forced to resign and sell CrossFit after his history of highly questionable remarks became public. But he kept the company jets and collected a $200m payout.

“He made a few political blunders and stupid errors of judgment that brought him an immense amount of backlash. He tried walking them back, he stepped down, and when that wasn’t enough, he ended up selling,” Marsh says. “It was probably a long time coming.”

But Glassman’s legacy on fitness is undeniable “in ways that are so broad that they’re hard to believe”, Marsh says. CrossFit’s revolution, he says, was not just the manner and equipment of working out, but the social culture of it.

“CrossFit’s unique quality was its community-oriented classes,” Marsh, who met his wife at a class, says. “They were very social, close-knit, and people built relationships in ways that would not happen if you just went to the gym with your headphones on.”