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 training with King Kai, whose planet is 10x Earth's normal gravity. 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 normal gravity.
On his way to Namek, Goku trains in a Capsule Corporation spaceship designed by Dr. Brief. It contained a Gravity Machine to artificially enhance gravity. He trains up to 100x the Earth's normal 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. After seeing Vegeta training in it, Yamcha also tries to train in the gravity chamber, with 300x Earth's normal gravity. However, he fails to withstand it. In his battle against Pui Pui, Vegeta describes having trained with 450x, possibly scaled back to avoid being injured as before.
Several years later, in the Baby Saga, while the heroes Goku, Pan, and Trunks are in space looking for the 7 Black Star Dragon Balls, Giru detects the One-Star Dragon Ball in a Deserted Spaceship which is about to fall into a star 70x Earth's normal gravity. After claiming the One-Star Dragon Ball, the heroes attempt to escape it's gravitational pull, get aboard their ship and fly off before time runs out. After trying to use their space scooters to escape, seeing how they cannot withstand the suns force, they decide to fly instead. However, Pan is seen slowly being pulled back, struggling to propel herself forward from the star's gravitational pull.