Other countries took note. Gone, suddenly, were the matronly 20‑somethings like Larisa Latynina, who had competed in the 1958 World Championships while pregnant. By 1977, Comăneci writes in her memoir, Letters to a Young Gymnast, the new gymnast “was smaller, younger, leaner, and focused not only on mastering technique but also on pushing the envelope on each apparatus to achieve the maximum level of difficulty and the highest possible score.” She added, “It also meant that there was very little margin for error—if a gymnast made the slightest mistake, her chances of victory were dashed.”

Girls all over the world, and especially in the United States (I was one of them), wanted in on the revolution. The conditions were right for what we might call the Roger Bannister effect: Once Nadia did it, others thought they could do it too. Feminist stirrings in the 1960s and the passage of Title IX in the ’70s meant girls were encouraged to be more athletic than ever, making the old-style women’s floor and beam exercises look staid. And radical improvements in equipment—the addition of springs to the floor mat and bouncy fiberglass to the wooden bars—further enabled physical innovation.

Within the span of a few years, women’s gymnastics became a hugely popular and fast-paced sport, featuring not only demanding dance elements but risky, high-flying moves that had been unthinkable in the early ’70s. At the 2012 Olympics, the American gymnast McKayla Maroney performed an Amanar vault—considered one of the most difficult skills for women—and got more air than Kōhei Uchimura, the male all-around champion. Maroney’s vault was also evidence of another dramatic shift: Over the decades, as Romania’s and Russia’s teams have declined, the United States has become a dominant force in gymnastics.

The initial Eastern-bloc-driven revolution is the backdrop of Dvora Meyers’s The End of the Perfect 10: The Making and Breaking of Gymnastics’ Top Score—From Nadia to Now, but the book’s real focus is the subsequent evolution of the sport, in particular its more recent rise in the United States. Meyers, a journalist, offers a strikingly optimistic take, very different from the sportswriter Joan Ryan’s account in Little Girls in Pretty Boxes in 1995. Ryan portrayed an elite gymnastic world rife with abuse, eating disorders, and emotional misery. She placed the blame largely on Béla Károlyi and his wife, Márta, whose relocation to the U.S. in 1981 helped lift American women’s gymnastics to new heights, in part by extending the ruthlessly authoritarian approach Károlyi had honed at home.

Writing two decades later, Meyers offers a much more upbeat view as she chronicles the growth of elite women’s gymnastics in the U.S. in the post-Soviet era. Today that world is home, she argues, to a greater diversity of body types, races, and ages, as well as of coaching practices. She also makes the case that high-level American gymnasts have more choices and agency than ever before. Much of the credit for this, Meyers suggests, can be ascribed to another striking change in the sport: the introduction of a new scoring system that emphasized athleticism and rendered the “perfect” 10 obsolete. As she points out, Simone Biles, American gymnastics’ current “It Girl,” is, at 19, more muscular and broad-shouldered than the waifish 14-year-old Dominique Moceanu was in 1996, in the Károlyis’ heyday. If Romania had qualified for Rio—shockingly, the team failed to make the cut in April’s qualifiers—Biles would likely have competed against 28-year-old Cătălina Ponor. Little girls no more.