Lance Armstrong persevered through the most difficult bicycle races on the planet and survived testicular cancer, but this week, the 40-year-old found a battle he had no interest in continuing. Armstrong said late Thursday night that he will stop fighting allegations that he used banned substances during his stellar career.

After Armstrong’s announcement, the U.S. Anti-Doping Agency said it would ban the cyclist for life and recommend he be stripped of his record seven Tour de France titles.

“It is a sad day for all of us who love sport and our athletic heroes,” said Travis Tygart, chief executive of the USADA, which led the latest charge to expose Armstrong as a cheat. “This is a heartbreaking example of how the win-at-all-costs culture of sport, if left unchecked, will overtake fair, safe and honest competition.”

Tygart and USADA charge that Armstrong’s wins, which made him a global sports icon following his battle against cancer, were aided by banned substances, including steroids and blood doping. In deciding to give up his fight, Armstrong still maintained his innocence, saying the wins were legitimate and within the rules.

“There comes a point in every man’s life when he has to say, ‘Enough is enough.’ For me, that time is now,” Armstrong said in a statement Thursday night.

Armstrong called the USADA investigation an “unconstitutional witch hunt” and said he saw no reason to participate in any further proceedings that might clear his name.

“If I thought for one moment that by participating in USADA’s process, I could confront these allegations in a fair setting and — once and for all — put these charges to rest, I would jump at the chance,” Armstrong said. “But I refuse to participate in a process that is so one-sided and unfair.”

The fate of his Tour de France titles now lies with the International Cycling Union, the sport’s governing body.

In June, USADA announced it had assembled 10 former Armstrong teammates who were willing to testify that Armstrong cheated, and it had also found tests results that were “fully consistent” with blood doping.

Armstrong, who retired from professional cycling in February 2010, responded by suing the agency, hoping to block the case from going forward.

Armstrong questioned USADA jurisdiction in the matter, saying, “At every turn, USADA has played the role of a bully, threatening everyone in its way and challenging the good faith of anyone who questions its motives or its methods, all at U.S. taxpayers’ expense.”

On Monday, U.S. District Judge Sam Sparks threw out Armstrong’s case but noted that
USADA’s “conduct raises serious questions about whether its real interest in charging Armstrong is to combat doping, or if it is acting according to less noble motives.”

Armstrong had the option of going to arbitration but announced late Thursday that he would stop contesting the matter.

“The toll this has taken on my family, and my work for our foundation and on me leads me to where I am today — finished with this nonsense,” he said.

Armstrong shared a familiar defense Thursday, noting that he had been tested his entire career in a variety of ways and results never showed conclusively that he violated any rules, even though whispers, rumors and allegations mounted in recent years.

“Whatever they asked for I provided. What is the point of all this testing if, in the end, USADA will not stand by it?” he said.

USADA oversees anti-doping efforts in Olympic sports in the United States. The agency does not have the authority to bring criminal charges but is empowered to levy charges that result in suspensions and the rescinding of awards.

The U.S. Attorney’s Office in Los Angeles investigated doping allegations against Armstrong for nearly two years, ending its probe in February without filing any criminal charges.

While the record books soon will likely no longer reflect that Armstrong ever won a Tour de France, the cyclist apparently is at peace with his career and accomplishments.

“I know who won those seven Tours, my teammates know who won those seven Tours, and everyone I competed against knows who won those seven Tours. . . . Nobody can ever change that,” he said.

Armstrong had spent years cultivating his wildly successful and familiar brand around the idea of perseverance and overcoming adversity. Armstrong won his first Tour de France title in 1999, three years after he had testicular cancer diagnosed. His fame transcended the sports world, as his books became bestsellers and his foundation raised millions of dollars with its iconic yellow “Live­strong” bracelets.

Armstrong said he will focus his efforts on his foundation, which he says has raised nearly $500 million to fight cancer.

“We have a lot of work to do and I'm looking forward to an end to this pointless distraction,” he said.