Today's athletes also train harder than ever before. Roger Bannister, who in 1954 became the first person to run a mile in under 4 minutes, trained for only 35 minutes a day. "That's barely considered a warm-up today," Abbott writes in her article.
But what happens when athletes push themselves too hard?
Some athletes may develop a condition called Unexplained Underperformance Syndrome (UPS), or overtraining syndrome. Symptoms include increased rate of infection, general fatigue, muscle ache, and stomach problems. As many as one in ten athletes may develop UPS.
"Almost everyone recovers from UPS," Jim Giles, a Nature reporter who wrote about the condition, said in a telephone interview from London.
But UPS can ruin an athlete's preparation for major events. "One sports scientist told me that if an athlete gets it before competition, it's all over," Giles said.
What causes UPS is under heavy debate. According to one theory, athletes may damage muscle by overreaching. To deal with this damage to the tissue, levels of some cytokinesmolecules used to exchange signals between cellsincrease.
As well as calming inflammation, cytokines suppress the ability of immune system cells to attack pathogens, leaving athletes vulnerable to illness.
One precaution that athletes should take to avoid UPS is to rest at least six hours between training sessions, according to Michael Gleeson, a sports scientist at Loughborough University in Leicestershire, England.
"Psychological issues seem to be quite a big factor as well," Giles said. "But no one knows exactly how those contribute to the physiological changes."
To some people, elite sports may be deadly. Last year, Cameroonian soccer player Marc-Vivien Foé died while playing a match. Seven months later, so did Hungarian footballer Miklos Feher.
Both athletes suffered from an inherited heart condition called hypertropic cardiomyopathy (HCM). It is the leading cause of sudden death in people under the age 30, according to Nature. The median age of HCM sufferers who die while engaged in sports is just 17 years old.
HCM is caused by the accumulation of an abnormal protein inside sarcomeres, a basic component of heart-muscle cells. This causes the cells to grow too large. As the muscles thicken, the heart can develop an irregular beat and runs the risk of stopping completely.
According to Nature, about 0.1 to 0.2 percent of people in the world have HCM. Each year about one percent of these people die. The extra strain of excessive exercise is believed to be able to trigger sudden death in people with HCM.
In Athens the Olympic athletes will also face human-made obstacles. The Greek capital, home to more than three million people, is one of Europe's most polluted cities.
Two pollutants of great concern are ozone and particulates (tiny bits of soot and other matter), both of which can irritate the lungs and cause asthmatic symptoms. On particularly bad days, the ozone levels in Athens far exceed the levels deemed healthy by the World Health Organization.
Outdoor athletes, such as cyclists, are most at risk. Elite athletes can cycle about 150 liters of air in and out of their lungs every minute during competitionten times more than "normal" humans. This, of course, exposes them to more pollution. They also inhale much more deeply, taking pollutants into the deepest regions of the lungs, Nature writes.
But Athens's pollution problem may be lighter than that of the upcoming 2008 summer games in Beijing. There, the particulate concentration is three times higher than it is in Athens.
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