The "fourth gear" is a new move developed by Luffy during his two-year practice, fighting with beasts as big as monsters in order to subdue them. Luffy in this state has a strong huge body and elasticity, and can even fly in the air with elasticity like a monkey.

However, after entering the "fourth gear", you can't stand normally, so you can only use the elasticity of rubber to bounce. Moreover, the "fourth gear" cannot be used for a long time because of the tight time and radical consumption. Once you change from the fourth gear to the original one, you can't use domineering for 10 minutes.

Extended data:

In the "fourth gear" state, Luffy can fly at high speed by compressing the foot muscles injected with air into the inner thigh and using the elastic force released by the elastic legs and feet, or it can temporarily stay in the air, similar to the "moon walk" in one of the six formulas. However, compared with walking on the moon, the fourth gear is much faster and the steering in the air is more flexible.

Luffy is very confident in the strength of his fourth gear. Luffy said to Doflamenco, "This will make you unable to fight back." Then he gave Doflamenco a beating. Later Luffy explained to the arena that the fourth gear only needs one punch to solve Doflamenco, and then it will knock Doflamenco down with one punch.

Baidu encyclopedia-fourth gear