Dragon Ball Z - episode 19 - 12 Sep, 1989

Gohan's training with Piccolo continues to intensify, but it's Goku who faces the biggest challenge. Goku begins his training, but it is unlike anything he's ever experienced before. The intense gravity of King Kai's planet makes training difficult, but when he learns that the Saiyans are used to extreme fighting conditions, Goku is inspired to give it his all. But will it be enough? (Source: dbzepisode.org)