Luffy's elasticity powers are a result from eating the Gum-Gum Fruit, which makes him virtually immune to all blunt force attacks except attacks filled with Haki. The fruit also gave him the ability to stretch at will. Combined with the elasticity of his body, he uses that ability to accelerate parts or the whole of his body as if shot by a slingshot to deliver punches, kicks, headbutts, body checks, or simply for propulsion. But like everyone who consumed a Devil Fruit, Luffy is unable to swim and when drenched in sea-water or in contact with an artifact blessed by the sea quickly loses his strength. He also has great physical strength as he was able to knock over 2 large apartment buildings at the same time (Water 7 arc).
Luffy develops two techniques to improve on his rubber abilities. The first of these is Gear Second. He uses his legs as a pump to increase his blood vessels, causing it to increase his attack power and overall speed instantly. However, the technique drains his stamina and if overused makes him temporarily unable to move afterward, as well as shortening his life span. The second is Gear Third, which is activated by biting a hole into his thumb and blowing air into his bones. He is then able to move the air around his bone structure and strike with limbs comparable in size to those of giants. The side effect to using Gear Third is that Luffy temporarily shrinks to a fraction of his normal size after releasing the air for a length that corresponds to the amount of time he was using Gear Third. He is capable of using both techniques simultaneously.
Further into the series, Luffy demonstrates the still innate ability to use Haki (覇気?, lit. "ambition") to make people or animals in his proximity faint. Additionally, this ability can negate a devil fruit users power and allow physical contact and damage. He has a very rare variation of Haki, "King Ambition". He first used it on Motobaro without realizing what he did.
