Wieber’s parents, Rita and David, knew they had something special even when Wieber was an infant. Her calves were not puny or Pillsbury Doughboy mushy like the other children’s — they were muscular and strong. Her biceps were so defined that other parents began to ask if Jordyn lifted weights.

With a budding athlete on their hands, the Wiebers enrolled Jordyn in official gymnastics classes when she was 4. Seven or eight years later, she showed up at a developmental camp hosted by Martha Karolyi, the women’s national team coordinator, and she caught Karolyi’s eye.

Karolyi said Wieber stood out because she was so intense, so businesslike and so strong — both physically and mentally — even though she was so young. Wieber never hesitated when she was asked to do a skill, Karolyi said, and she never celebrated too much when she mastered something or wallowed too much when she failed.

“She wasn’t a smiley person; she was in her own world,” Karolyi said. “But I had Nadia Comaneci, who wasn’t a smiley person. And we were asked, Why is she not smiling? Because she is focusing, she is minding business. That’s the type of gymnast that’s Jordyn. I could compare the toughness to Nadia.”

Martha’s husband, the renowned coach Bela Karolyi, also extolled Wieber, saying she would be unbeatable in London. He said she also reminded him of Comaneci, the Romanian gymnast whom he and his wife coached to the first perfect score of 10.0 at an Olympics.

He described Wieber as having thick, strong bones and the body constitution of someone who never would break.

“She especially has that sturdiness,” he said. “But the best thing might be is that she can turn things around when other people are failing.”