Joey Chestnut says he's been training like Rocky in the Rocky IV montage -- killing himself to get his 4th of July hot dog eating title back ... and says he's in the BEST eating shape of his life!!!!
Chestnut -- sporting a playoff beard -- shockingly lost his championship belt to Matt Stonie last year -- who destroyed 62 hot dogs in 10 minutes ... defeating Chestnut, who only put down 60.
But Joey tells TMZ Sports ... he's been busting his ass to get back in top form -- and brags that he recently broke his own wiener record of 69 .