Millions of eyes will tune in Sunday morning to watch as Spandex-ed, chalk-covered women gymnasts rocket themselves into space and maneuver their bodies into otherworldly contortions for the qualifying rounds. The U.S. women’s team, which includes 4-foot-9 phenomenon Simone Biles and returning gold medalists Gabby Douglas and Aly Raisman, are known as the “Fierce Five” for their daring domination in the sport that is the darling of the summer Olympics. But behind the power, skill, and muscled thighs is a disturbing report on what many say has been an open secret for decades: allegations of widespread sexual abuse by top coaches.

Officials in one of the sport’s national governing organization, USA Gymnastics, admitted under oath that they had routinely dismissed allegations about predatory coaches and failed to alert authorities to the problem. An investigation, published yesterday by the Indianapolis Star, found that USA Gymnastics ignored multiple warnings about famous coaches, including William McCabe, a Georgia coach who was allowed to molest vulnerable girls and young women for years. (He is currently serving a 30-year sentence for the sexual exploitation of children.)

The disturbing cover-up is just the latest example of how competitive gymnastics is one of the most dangerous sports for girls.

Take this statistic from the CDC: the graceful art of gymnastics is second only to football in terms of injury-prone college sports. “You can’t believe the level of abuse that goes on,” said Robert Malina, a retired professor of kinesiology and health education at the University of Texas at Austin, who has studied the growth of gymnasts and other young athletes for decades.

In one example, last spring, two former Penn State gymnasts told the school’s newspaper that their coaches routinely demeaned them, pressured them to continue to practice through injuries, and critiqued their weight. One young woman, Shaelyn Farley, was forced to train through a chronic knee injury that required six surgeries. Farley said her coaches were so cruel, she considered suicide.

Malina’s research has similarly found that many young women endure years of brutal training and sustain multiple injuries in grueling regimens that go unmonitored.

A 1995 book, Little Girls in Pretty Boxes: The Making and Breaking of Elite Gymnasts and Figure Skaters, revealed the physical and psychological abuse girls endure in order to pursue Olympic glory. The book started with the tale of a girl who broke her neck and went on to detail starvation diets and the tyrannical rule of the former U.S. coach, Bela Karolyi, whose wife Marta assumed his position and is soon retiring. But the popularity of the U.S. women’s team, which has earned medals in the last eight Games, has helped fuel the sport’s growth. “People have been talking about this for years,” Malina said. “But nobody blinks an eye so long as you’re winning.”

As the sport has grown more competitive, the training has become ever more rigorous, said Keith Russell, a retired professor of anatomy at the University of Saskatchewan and former gymnastics coach of men’s national Canadian team who has also studied the sport’s effects on growing bodies.

“If one gym requires 30 hours of training, the one in the next town bumps theirs up to 32,” said Russell. “So the next one demands 35.”

And it’s not just the most elite athletes who are suffering from the increasing pressure. “Everybody’s hoping for a medal but of course not everyone’s going to get one,” Malina said. “The coaches don’t let (the kids) leave—and the parents often go along with it.”

Malina once asked a longtime gymnastics official about why he refused to allow girls who had no future in the sport to drop out. “He told me, ‘No, I won’t. We need the money.’ I can’t make that up.”

This disturbs Malina, who spoke frankly from his cattle ranch near the Gulf of Mexico about his experiences with USA Gymnastics. “(Parents) just drop off their kids for two or three hours and come back to pick them up. Who’s asking, ‘To whom am I entrusting my daughter for 30 hours a week?’”

In a number of cases, parents were unwittingly entrusting their child to a sexual predator. The Star’s report found that the Indianapolis-based USA Gymnastics compiled complaint dossiers on 50 coaches, but instead of turning them over to the authorities, simply filed them away in a drawer. Some of the reports are nausea-inducing: Marvin Sharp, named the 2010 national Women’s Coach of the Year, was later accused of touching one adolescent’s vagina, and of shaving her pubic hair with an electric eyebrow razor he just happened to have with him. He also ordered connecting hotel rooms during travel events, and insisted on keeping the door open. Arrested in 2015, he killed himself in jail. Rhode Island coach James Bell went on the lam after police learned that he’d been abusing girls as young as 10; he’s now serving eight years in prison on child molestation charges. And Tennessee coach Mark Schiefelbein was also locked up for aggravated sexual battery against a 10-year-old; prosecutors discovered a long history of complaints against him.

All of these men had been reported to USA Gymnastics, which did not alert the police, and the coaches went on to abuse at least 14 underage girls before being caught.

USA Gymnastics responded to the Star’s report with a written statement by president Steve Penny. He didn’t challenge any of the paper’s findings, but said it omitted “significant facts that would have painted a more accurate picture of our efforts.”

Regardless, the organization perhaps had an interest in keeping the grim allegations under wraps. USA Gymnastics’ aim is to develop the U.S. Olympic team and advance the sport nationwide. With more eyes on the U.S. women’s team than ever, popularity has surged. The group now has more than 121,000 athletes as members, and 3,000 gyms around the country.

Meanwhile, the sport’s international governing body, the Federation Internationale de Gymnastique, or FIG, has been attempting to address concerns about the overall treatment of girls. In 2009, Russell, the professor of anatomy, was appointed president of FIG’s scientific commission and Malina, the kinesiology expert, also served on an FIG committee to address the effects of training on gymnasts’ growth, focusing on sexual and skeletal maturation.

At least one concern about the sport—that it stunts gymnasts’ growth—has been soundly disproven. “The physical act of gymnastics training does not affect growth and size,” Russell said. “Training for gymnastics doesn’t make women any smaller, just as playing basketball doesn’t make players any taller.”

Rather, a review of decades of studies from around the world shows that gymnasts, it turns out, just have short parents. (Raisman and Madison Kocian are the U.S. team’s tallest members at 5-foot-2.)

For Malina, the most disturbing thing about the sport is its culture—one dominated by adult men supervising very young girls. “What we don’t know,” he said, “is the long-term effect of the gym’s environment on the girls’ minds,” he said.