One question asked by Gibney, who narrates the film, is why an athlete whose reputation seemed secure after his retirement returned to competition. Was it a sense of invincibility? Was it the prospect of a future without the thrills and risk-taking of his glory days?

The first half of the film looks back on Armstrong's youth, when he was a ferociously competitive, self-described bully. His stated belief that "losing equals death" was probably reinforced by his near-miraculous recovery from testicular cancer through treatment that included brain surgery in late 1996. The following year, he founded what became the Livestrong Foundation for cancer research and the support of cancer survivors. The film barely addresses the accomplishments of Livestrong, from whose board Armstrong resigned in November 2012.

The second half focuses on Armstrong's return to competition without the benefits of the blood booster EPO, testosterone, human growth hormone or blood transfusions. Or so he maintains. In that competition, he placed third. The film goes into clinical detail about how such drugs and procedures enhance performance.

Instead of bombshell revelations, of which there are none, "The Armstrong Lie" offers a thorough history of Armstrong's cycling career and the elaborate measures he took to cover his tracks. Interviews with former colleagues like Frankie Andreu and George Hincapie portray Armstrong as a scary, vindictive control freak who pressured fellow riders to take drugs and enforced a code of omerta. Doping was so widespread and its benefits so pronounced that serious competitors had little choice but to go with the program.

The movie rehashes the vigorous assertion by Andreu's wife, Betsy, that she was in the hospital room in 1996 when Armstrong admitted to cancer doctors that he used performance-enhancing drugs. To this day, Armstrong denies her story. Michele Ferrari, the Italian sports doctor who is serving a lifetime ban from Olympic sports for doping athletes, describes his quest for more and better enhancement. He comes across less as a demonic enabler than as a detached scientist.

The movie has wonderful footage of the 2009 Tour de France, in which Armstrong came from behind to take third place. The winner, the Spanish cyclist Alberto Contador, is described as a younger version of Armstrong. Long-distance shots of cyclists riding by a field of sunflowers and over bridges add a touch of beauty to the film, while other sequences shot in the midst of competition provide blasts of adrenaline.

More glaringly than most sports documentaries, "The Armstrong Lie" reinforces the sad truth that the adage "It's not whether you win or lose, it's how you play the game" doesn't apply to professional sports. Maybe it never did. Winning is everything.

"The Armstrong Lie" is also a reminder that celebrity and hero worship, once attained, are almost irresistibly addictive. Armstrong, for all his gifts and hard work, emerges as a hollow man, corrupted by glory, protecting what remains of his reputation. Even in disgrace, he is determined to "control the story."

Gibney, who admits to having been "a fan," explored this kind of hubris more forcefully in his documentary "Enron: The Smartest Guys in the Room" (2005), whose villains had none of Armstrong's glamour. Fallen idols die hard.