In the first week of competition at this year's Olympic Games, nine world records fell in the swimming pool, including 17-year old Missy Franklin's new standard in the 200-meter backstroke and Rebeccas Soni's personal best in the 200 breaststroke, even though many of the previous records were set by swimmers wearing now-banned extra-buoyant suits.
Chinese weightlifter Zhou Lulu beat Russian rival Tatiana Kashirina with a combined total of 333 kilograms (734 pounds) in a two-part event, after Kashirina became the first woman ever to snatch more than 150 kilograms (331 pounds). And on the track, Usain Bolt broke the Olympic record in the 100 meters, coming with 0.05 seconds of his world record mark of 9.58 seconds.
After more than 100 years of modern Olympic competitions -- alongside often-repeated claims that the human race is butting up against the limits of athletic performance -- how is it that athletes keep getting better?
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The answer, experts say, involves a combination of incremental technological improvements, as well as a growing population of people attempting a larger variety of sports that they start earlier and stick with longer.
The mind plays a big role, too, especially when it comes to toppling seemingly insurmountable barriers, like the four-minute mile of the past or the two-hour marathon of the future.
"There is almost certainly a species limit in terms of physical capabilities, and I suspect we might be in the range of that," said Carl Foster, an exercise physiologist at the University of Wisconsin, Lacrosse. "But every time scientists say humans are not going to go any faster, they've been shown to be wrong. You can take that one to the bank."
In nearly every sport, from running to rowing to cross-country skiing, athletes have been getting faster over the last 75 years. But as time has passed, the rate of improvement has slowed down, leading many experts to speculate that we are reaching the limits of human athletic performance.
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Through calculations of maximum power output, oxygen use, heart function and other factors, some researchers have attempted to predict what the absolute limits of human ability will be. Much-debated estimates include 1:58 for the marathon (a five-minute improvement over the current men's record of 2:03.38), and 9.48 for the men's 100m.
For now, performances keep getting better. One reason (excluding suspected and confirmed doping scandals), Foster said, is that professional athletic opportunities have exploded in sports beyond the traditional options of football, basketball, baseball and hockey. The best swimmers, gymnasts and runners can now make a living at sports that once petered out at the college level -- allowing them to focus on training and recovery instead of squeezing workouts in around full-time jobs.
Inspired by media exposure during Olympic events and drawn in by an abundance of youth programs, kids are starting sports at younger ages. And with improvements in sports medicine, athletes are often able to compete long into their 20s and 30s.
For skill-based sports like swimming, an extended career can give an athlete the time needed to fine-tune techniques and maximize efficiently. And with plenty of airtime on TV and YouTube, along with easy access to slow-motion replays, including underwater cameras in the swimming pool, amateur athletes and coaches can now learn from the pros in ways they never could before.
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One of the biggest reasons athletic performances continue to improve is simply a matter of numbers: More people in more places are trying more sports, increasing the chances that individuals with innate talent will end up in a sport they'll excel at.
After Title IX paved the way for women to participate en masse in sports in the 1970s, women's world records fell rapidly for decades before finally leveling off.
Likewise, both men's and women's running records got faster after the 1968 Olympics in Mexico City, where East African runners had great success, inspiring kids from the area to give the sport a shot. And some of the best swimming performances in London came from Chinese swimmers, who were likely drawn to pursue the sport more seriously after watching the action in Beijing.
With the Jamaicans dominating many track events this year, there's likely to be a popularity -- and a performance -- boom emerging from the Caribbean Islands, said Michael Joyner, an exercise researcher at the Mayo Clinic in Rochester, Minn. Still under-represented in sports but likely full of potential, he added, are athletes from India and South American countries, and Native Americans from the Four Corners region of the United States.
Technological advancements often play a role in incremental improvements, too, Joyner said. Lighter bikes, deeper swimming pools, fiberglass pole-vaulting poles, synthetic tracks: Each improvement propels athletes to better performances, even if they're no more fit or talented than their predecessors.
When someone finally does break a time-to-beat, a fresh record can give the next generation of Olympians a whole new idea of what's possible. When inspired, the mind can exert powerful control over the body.
"There's no evidence that people going faster today have better engines than people 30 or 40 years ago," Joyner said. "Believing something can be done frequently means it can be done."