Finally, hard evidence GB Packers running back Eddie Lacy took up the offer to train with P90X creator Tony Horton -- and we gotta say ... the dude looks like he's already getting results.

Check out the photo Tony's training pal Bobby Stephenson posted on Facebook -- showing Eddie and Tony after a workout with the caption, "Crushing Shoulders and Arms P90X Style."

Packers coach Mike McCarthy had said he wanted Lacy to shed some serious LBs before next season -- and that's when Horton volunteered his services.

Check out what Lacy looked like 31 weeks ago ... looks like Lacy is taking the workout plan very very seriously.