As the Olympic Games began in London, so too did the debates focusing on the medical implications of becoming a world-class athlete. Are those flat-chested, prepubescent, 17-year-old gymnasts subjected to training that’s akin to child abuse? That’s what some pediatricians called it in a 1996 review study published in the New England Journal of Medicine. And how much do those blood transfusions improve an athlete’s performance? Enough to justify forcing the return of medals by Olympic athletes who admit to “blood doping”?

Harvard Medical School historian Dr. David Jones raised such questions in a paper published last Wednesday in the New England Journal of Medicine that examined the past 150 years of journal publications — even before the modern Olympics were revived in 1896 — to see what doctors thought of extreme exercise such as the 26.2-mile marathon.

“In 1900, it would have been inconceivable to doctors that tens of thousands of people would eventually be running marathons,” said Jones. The medical world back then assumed that only a handful of elite individuals had the endurance to finish such a race. Experts back then also believed that excessive training left adolescents “listless and stupid,” as one researcher contended in an 1867 journal article.

Other myths that have since been debunked: Participation in any type of sports would impair a woman’s fertility, and that the human body wasn’t capable of running a mile in less than four minutes. The current world record is 3:43.13.

“What’s the limit of human performance? We still don’t know,” Jones said.

He also wondered how much of our current conventional wisdom will hold up in the next century. For example, many have contended that Olympic swimmer Michael Phelps has unique genetic advantages that have earned him a place on the medal stand 16 times (and counting).

As Los Angeles Times science writer Jon Bardin wrote in a recent article, “There are numerous genetic factors known to confer advantages in athletic contests from mutations that increase the oxygen carrying capacity of blood to gene variants that confer an incredible increase in endurance, and these mutations appear to be especially common in Olympic athletes.”

Gene therapy could become the next version of doping, which the World Anti-Doping Agency is currently trying to combat by discouraging the use of genetic testing to assess athletic performance and by encouraging research to detect the use of gene therapies designed for medicinal purposes to, say, increase muscle growth or endurance.

The experimental drug repoxygen — a gene therapy being tested for the treatment of anemia ­— was purportedly used by some athletes in the 2006 Turin Winter Olympics to increase the production of red blood cells, akin to having a blood transfusion.

But Jones said he doesn’t put much stock in the power of genes either naturally inherited or manipulated through medicine. “Just as there’s no one gene for intelligence,” he said, “I don’t think there’s one gene, or even an assemblage of genes, that ensures athletic performance. Genes may play a role at the elite levels seen in the Olympics, but so does training, access to resources, and even luck. I always laugh when commentators credit genes — there’s so much more going on than that.”

On the other hand, certain agents, like steroids, can give athletes a real edge by helping them build more muscle, and the health risks justify their ban from Olympic sports. “The Games are hopefully cleaner than they were 20 years ago,” said Jones, “but I wouldn’t be surprised if there are things being used that aren’t being detected on tests.”

While blood transfusions to increase red blood cell counts are banned, there’s no rule against an athlete training at a high altitude, which also increases red blood cells.

But how much these technologies increase the odds of winning is unknown. Nor do scientists completely understand how much of a role gender plays. The gender gap in performance has been decreasing, but that hasn’t stopped the International Olympic Committee from instituting new rules on gender testing to determine whether certain female athletes have too much male testosterone.

“I wouldn’t be surprised if 50 years from now,” said Jones, “people will look back and wonder why we obsessed so much about things that don’t actually make a difference in athletic performance.”