LONDON — Back when an Iron Curtain still cleaved the globe, a pint-sized Russian captivated the world with her elegant gymnastics and her gap-toothed smile. Olga Korbut was as flexible as a rubber band and graceful as a sprite at the 1972 Olympic Games, when she won three gold medals by following her mother's advice: "Be careful, be first and be joyful."

Forty years later, women's gymnastics have become so technically rigorous and physically demanding that the battle for Olympic gold leaves little room for the artistry and joy that have made the sport one of the Games' most popular.

At the 2012 Olympics, where Thursday the world's top 24 women's gymnasts compete for the prestigious individual all-around title, grimaces have outnumbered smiles on the competition floor, as gymnasts gird for two-and-a-half twisting vaults that defy gravity and gulp lung-fulls of oxygen to complete tumbling sequences that hammer joints and limbs.

The bliss seems to come only afterward. And even then, it often looks more like colossal relief over having escaped unscathed to earn a hug No doubt, there's a danger of reading too much into a grin or the lack of one. But with the sport's difficulty escalating so rapidly, it's no wonder the "game face" of modern-day gymnasts tends to be a clenched jaw rather than a radiant smile.

That's because the sport's judging criteria, known as the code of points, rewards difficulty over artistry. While it was intended to take much of the subjectivity out of judging and encourage the evolution of gymnastics skills, some fear it has done so to a fault.

Even Bruno Grandi, head of the sport's international governing body, has sounded an alarm over a system he feels is out of whack, calling it "a time bomb that we are wholly unable to contain." What troubles Grandi is that the line between gymnastics and acrobatics is blurring. The former is intended as an artistic statement; the latter, purely athletic.

In their quests for higher "difficulty" scores, today's gymnasts are packing their routines with so many demanding, high-risk skills that there's little room left for artistry.

It's particularly evident in floor routines. In Korbut's day, the space in between tumbling stunts was filled with dance elements and expressive movements that wove a routine together.

Today, in the rush to rack up as many difficulty points as possible, the space in between stunts has been de-valued. It serves as the gymnastics equivalent of a rest stop on the New Jersey Turnpike, affording gymnasts a moment to suck in a gulp of air before attacking the next skill.

"There's a lot more at stake in terms of the skills that they're performing," explains 1984 Olympic gold medalist Peter Vidmar, 51. "But we're always looking for the complete package, aren't we? We want that great, great physical athletic performance. And we want that biggest smile in the world to go along with it."

This is the essence of sports: striving for perfection, whether to be faster, stronger or more skilled. And with each generation, the standard of perfection is raised.

"Guys that played baseball 20 years ago could not hang with baseball players today or match the speed, the fitness," said John Geddert, coach of the U.S. Olympics women's gymnastics team. "Gymnastics is the same way. The equipment is better. The training is better. All of that contributes to the sport evolving.

"Is the sport evolving faster than some others? Yes, I think it is. Our sport is pretty tough now. You've got to be a stud. You can't fake it here."

For young gymnasts with Olympic aspirations, the pressure to master ever more difficult stunts often takes a toll. And it's compounded by the persistent message, implicit in the judging system and reinforced by countless coaches, that their best is never good enough.

Says Shawn Johnson, the 2008 Olympic gold medalist on the balance beam: "We just kind of grow up with this mentality that you aren't ever fit enough; you aren't ever perfect. And I think that gets ingrained in everybody's mind. So you're constantly trying to be better. And you're constantly trying to find your worth in someone else - in what they say, how they perceive you, how they look at you. And it's hard."

But has the emphasis on athleticism over artistry done anything to reduce the joy of the performers or spectators? And can the answer truly be found on the faces of the athletes immersed in world-class competition? Joan Ryan wrote extensively about the physical and emotional consequences of elite-level gymnastics and figure skating in her 1996 book, "Little Girls in Pretty Boxes."

"They are among the youngest competitors at the Games," Ryan wrote in an email exchange about Olympic gymnasts. "They know little of the world beyond their sport. They are carrying the hopes of their parents, coaches and federation officials on their shoulders. They have one shot. And if they fail, they fail on the biggest stage there is. That's a lot to handle for teenagers who are barely old enough to drive. . . .

"Maybe we expect them to be more joyful than other elite athletes because unlike every other athlete in the Olympics, most of the female gymnasts look like children."

Just because a routine is physically grueling, Geddert says, doesn't mean it can't be artistic. Similarly, just because a gymnast doesn't telegraph joy doesn't mean she's not experiencing it.

Gymnasts manifest joy in different ways. Gabby Douglas, 16, who'll compete for the individual all-around title, radiates a smile that rivals Korbut's, which stretched from one pigtail to the other. Jordyn Wieber, by contrast, has never been "a smiley person," as U.S. team coordinator Martha Karolyi puts it.

Wieber's quest for all-around gold ended in tears, when she missed the cut for the finals. But she stormed back with a lion's heart two days later to help the U.S. to the team gold medal, proving the very definition of a champion.

"I think Jordyn enjoys what she's doing," says Geddert, who is also Wieber's personal coach. "I don't think any of these kids don't enjoy it because they put in 30, 35 hours a week training - and for 10 years. For some, maybe it's the challenge that's enjoyable. But if it's not enjoyable, you can't make them endure what they have to go through. I mean, we're in America! We can't make 'em do it."