Adrenaline
Super-human power
Most of us are familiar with the TV series “The incredible Hulk” in which the bodybuilder Lou Ferrigno played the role of the Hulk.
The process by which the scientist Bruce Banner usually transforms into the Hulk is presumably the result of the chemical catalyst, adrenaline (a.k.a. epinephrine). As in normal human beings, Banner's adrenal medulla secretes large amounts of adrenaline in time of fear, rage, or stress, which hormonally stimulates the heart rate, increases blood-sugar levels, and inhibits sensations of fatigue. Whereas the secretion heightens normal physical abilities in normal human beings, in Banner's case it triggers the complex chemical-extra-physical process that transforms him into the Hulk. The total time of transformation falls anywhere between seconds to 5 minutes, depending on the initial adrenalin surge, which will be determined by the original stimulus. Soon after the transformation, the amount of adrenalin in the Hulk will return to more normal, reduced levels. When the Hulk transforms back into Banner, the excess muscle mass and energy is lost, presumably to the same place he derives it.