Olympic gold medalist and defending all-around women's gymnastics world champion, Jordyn Wieber's lackluster performance in London has been a surprise throughout the games. The 17-year-old was expected to take home at least one individual gymnastics medal and to compete in the individual all-around, for which she didn't even qualify. Though as her coach revealed today, this could be due to an untreated stress fracture.

As Jo-Ann Barnas reported for the Detroit Free Press:

A spokesperson for USA Gymnastics said there hasn’t been a confirmed diagnosis of Wieber’s injury -- she hasn’t had an X-ray nor MRI exam -- but John Geddert, Wieber’s coach, said the unofficial diagnosis came from the “X-ray eyes” of team doctor Larry Nassar.

“He’s right, 99 percent of the time,” Geddert said. “She’s had soreness. And now there’s a lump there. So it’s all the signs of a stress fracture. She’s going in a boot tomorrow.”

As the AP reported, her injury may have been a problem as early as Olympic trials in San Jose in June. She had a sore right heel that may have contributed to her first loss during a meet in three years.

A stress fracture is usually due to very small cracks in the bone that are caused by repetitive overuse and repeated force absorption (like, say, sticking a vault landing?). According to literature provided by the American Academy of Orthopaedic Surgeons, fatigue is another factor: when muscles become too tired to help absorb shock, they transfer weight stress to the bone. Tennis, track and field, gymnastics, and basketball athletes are the most susceptible to stress fractures because they all have in common the repetitive movement of feet striking the ground.

Most stress fractures occur in the feet and lower legs, where the bones bear the most weight.

Of note, female athletes may be more susceptible to stress fractures. Explained the AAOS:

Medical studies have shown that female athletes seem to experience more stress fractures than their male counterparts. Many orthopaedic surgeons attribute this to a condition referred to as "the female athlete triad": eating disorders (bulimia or anorexia), amenorrhea (infrequent menstrual cycle), and osteoporosis. As a female's bone mass decreases, her chances of getting a stress fracture increase.

Indeed, among those who aren't elite athletes, some stress fractures may not be related to extreme physical activity and instead to bones weakened by osteoporosis. Those beginning a new fitness program are particularly susceptible, according to the Mayo Clinic.

Of course, we don't yet know any of the specifics of Wieber's case. And despite this reported injury, she still goes home with the shared gold medal in all-around team.