Other source:
Gohan's real training is about to begin, as Piccolo trains him in the martial arts. On Kami's Lookout, Yamcha, Tien, Krillin and Chiaotzu want to get the same training as Goku did. So, Mr. Popo takes them to the Pendulum Room where the past, present, and future intertwine. Krillin and the others use the room and are sent to Planet Vegeta in the past, facing two powerful Saiyan warriors. After a horrifying battle, the Z Fighters continue their training with more motivation.
