Lance Armstrong -- I'M BACK ON MY BIKE

For the first time since he was banned from pro cycling for LIFE, a sponsorless, titleless, cancerless Lance Armstrong was seen on his bike this week ... training ... just for the hell of it.

TMZ has obtained photographs of Armstrong in Waikoloa Village, HI yesterday -- riding his bicycle on a local highway with another rider.

Sources tell TMZ, Armstrong has been hanging around the Hawaiian town for the last week -- riding his bicycle, swimming at the local public pool, and visiting Hawaii Volcanoes National Park.

In the photos, Armstrong is wearing a Livestrong jersey, despite stepping down as chairman from the foundation earlier this month in the wake of his doping scandal.

He's also wearing a helmet made by Giro -- one of the sponsors that kicked Lance to the curb this month.

As for the bike, Lance's rep tells us Armstrong has traded out his iconic Trek for a Crumpton -- "a local bike maker from Austin, TX."

Lance's rep also says, "[Armstrong] will continue to stay active and try to be the fittest 40 year old out there (he's now 41)."