BEIJING — When Liu Xiang, China’s track and field superstar, crashed to the ground at the London Olympic Games on Tuesday after stumbling over the first hurdle in his 110-meter men’s hurdles heat, an announcer on the state broadcaster openly wept and subway riders thronging platform television screens gasped in horror.


But instead of the scorn and anger that met Mr. Liu four years ago when a similar injury to his Achilles’ tendon forced him from the Olympic stadium in Beijing just before the race began, the overwhelming majority of those using the nation’s most popular microblog site reacted with magnanimity and grace.


“I believe, I steadfastly believe that Liu Xiang is our hero,” wrote one user on Sina Weibo. “He was, he is, and he always will be.”


Within an hour of Mr. Liu’s dramatic tumble, millions had posted messages, most of them supportive and laudatory. If there were voices of disgust, they were directed at the Chinese government, with its rigid Soviet-style sports system and a single-minded fixation on winning gold medals.


“With this oppressive national sports system, he only had one choice — to win respect and hurt himself,” one fan wrote. Another writer called the tumble “an entire generation’s tragedy.”


By any measure, this should be a season of unvarnished celebration for China. It has pulled slightly ahead of the United States in the battle for medals, and the Games have produced a new national hero in Sun Yang, the first Chinese man to win an Olympic gold in swimming.


But in recent days, a tide of self-doubt and introspection about the human costs of China’s Olympic prowess has arisen amid worries that the nation’s draconian sports system is sometimes producing damaged goods. Floundering athletes can even be cast aside after their careers are over — a point driven home last year when a former gold medal gymnast was found begging on the streets of Beijing. According to the state media, 240,000 retired athletes are grappling with injuries, poverty and unemployment.


Sometimes the victors inadvertently reveal the sacrifices they were forced to endure during their years of training. Last week, shortly after winning her third Olympic gold medal, the Chinese diver Wu Minxia was told that her grandparents had died years earlier and that her mother had been diagnosed with cancer. Ms. Wu’s father explained that the family preferred to lie to his daughter all those years rather than risk harming her Olympic prospects.


“We accepted a long time ago that she doesn’t belong to us,” the father, Wu Yuming, told a Shanghai newspaper. “I don’t even dare think about things like enjoying family happiness.”


Like many Chinese athletes, Ms. Wu had been plucked from her family as an adolescent and sent to live at a state-financed sports academy, where training is grueling. Many athletes do not see their families for years. Last week, after Lin Qingfeng claimed a gold medal in men’s weight lifting, his father told reporters that he did not recognize his 23-year-old son, whom he had not seen for six and a half years, until he heard his name mentioned on television. “It’s been a long time,” Mr. Lin’s mother said, “since he’s had a meal at home.”


Yan Qiang, a veteran sportswriter, defended China’s emphasis on winning medals, saying they have helped to unify the nation. “We still need gold medals to boost social morale,” he said in an interview. “The people need it. And the athletes are willing to gamble their youth for a brighter tomorrow.”


The obsession with Olympic glory is inextricably tied to the country’s recent history. In the first half of the 20th century, Chinese intellectuals called their nation “the sick man of Asia,” lamenting its failure to produce Olympic-worthy athletes. Shortly after founding the People’s Republic of China, Mao Zedong sent a delegation of 40 men and women to the 1952 Summer Games in Helsinki, Finland; all but one arrived too late to compete.