Gravity (重力; Jūryoku) is a concept addressed frequently in the Dragon Ball universe.
Weight training (gravity times mass) is used early in the series as a means of acquiring strength. This begins with the use of weighted clothing, such as the shells worn by Goku and Krillin given to them by Master Roshi. Goku and Piccolo also later drop weights hidden in their clothes prior to battling Raditz.
Later, weight training is made more intense through a different means. Rather than add weight through clothing, heavier gravity environments are utilized. This begins with Goku trains with King Kai, whose planet is 10x the Earth's. The other human Z fighters later train here while the others are adventuring on Namek. Planet Vegeta and Planet Zoon also have 10 times the Earth's gravity.
Later, Goku trains in a Capsule Corporation spaceship designed by Dr. Brief on his way to Namek. It contained a Gravity Machine to artificially enhance gravity. He trains up to 100x the Earth's gravity in it and does various bodyweight exercises.
Vegeta (who would have access due to Bulma being his wife) was seen training with even greater extremes. In the Garlic Jr. Saga he trains with 300x. In the Trunks Saga, Vegeta used it set to 500x, but was injured as a result. In his battle against Pui Pui he then describes having trained with 450x, possibly scaled back to avoid being injured as before.
Yamcha also tries to train in the gravity chamber, with 300x Earth gravity, after seeing Vegeta training in it. Although he was not able to stand it.