Lance Armstrong is fighting to not only keep his seven Tour de France titles, but also maintain his reputation as one of sport's most remarkable athletes.

The American lost his latest legal bid to halt the U.S. Anti-Doping Agency's case against him, which has come more than a year after his retirement from cycling and subsequent move to triathlon competitions.

The 40-year-old, who fought back from testicular cancer to win cycling's biggest race from 1999 to 2005, has described himself as the "most tested athlete in the world" and long denied any involvement with illegal doping.

"Lance has passed nearly 500 tests over 20 years of competition," declared spokesman Mark Fabiani in response to allegations from disgraced former teammate Tyler Hamilton -- who has admitted taking performance-enhancing drugs during his career.

However, the former chairman of the World Anti-Doping Agency, Dick Pound, has long argued that Armstrong was involved in the dark art of doping.

"Look all around him and everyone else is doing it, so what should you think?" Pound told the New York Times.

After months of legal arguments, the two parties are now left with no option other than solving the dispute between themselves. So where did the charges come from, and how did the two sides develop such a bitter relationship?

What are the charges?

In June 2012, the USADA charged Armstrong with doping and trafficking of performance enhancing drugs.

Along with the cyclist, several members of Armstrong's former team were charged. These included Luis Garcia del Moral and Michele Ferrari, both team doctors, trainer Jose "Pepe" Marti, team physician Pedro Celaya and Johan Bruyneel, director of the U.S. Postal Service (USPS) team.

"Armstrong is facing some pretty serious charges from USADA," explains Peter Flax, editor of Bicycling Magazine.

"He's been accused of the use of of prohibited performance-enhancing drugs and methods, as well as being involved in the possession, trafficking, and concealment of these activities. The list of drugs and doping methods is pretty much the kitchen sink of what was possible in the era in which Armstrong rode."

It is believed the charges stem from a federal investigation by Food and Drug Administration special agent Jeff Novitzky. His investigation didn't result in any charges, but Novitzky -- who led the fight against the Balco Laboratory and doping in Major League Baseball -- is understood to have helped with the USADA case.

What is the USADA?

The U.S. Anti-Doping Agency is the body responsible for monitoring in and out of competition drug testing for U.S. Olympic and Paralympic sports.

It is responsible for enforcing the World Anti-Doping Agency code, and its bans apply around the world.

"USADA's job is to protect clean sport rather than enforce specific criminal laws," its chief Travis T. Tygart said at the time of the federal case's collapse.

"Our investigation into doping in the sport of cycling is continuing and we look forward to obtaining the information developed during the federal investigation."

What is the evidence?

The USADA alleges that Armstrong took steroids throughout his career, and says it has testimony from former teammates to support the charges. The organization has refused to reveal who has provided the evidence.

"A significant number of Armstrong's former teammates, in return for immunity or preferential treatment from USADA, have testified about doping activities that they participated in or witnessed," Flax told CNN.

"Some of them, like Floyd Landis, are people who have made public accusations in the past, but others -- most notably George Hincapie, Armstrong's most loyal lieutenant during all seven of his Tour de France victories -- have never offered testimony about doping on that team."

Landis, a rider with the USPS team from 2002 to 2004, has publicly claimed that he saw Armstrong using blood transfusions to increase the level of oxygen-carrying red blood cells in his system, as well as taking the blood-boosting drug EPO.

In 2006, Landis became the first person other than Armstrong to win the Tour, but was stripped of the title for failing a drugs test. The disgraced cyclist has even gone as far as accusing Armstrong and Bruyneel of paying the International Cycling Union (UCI) to cover up a positive test in 2002.

Armstrong dismissed the charges, and accused his former colleague of threatening riders with drug allegations.