From a mate whos a chemist.
A general class of decongensants but also has stimulant effects, found in party pills at raves to help clear the senses and give you a high.
They're all isomers of methylhexanamine, similar compositions but different structures
chemical ways of getting around drug restriction laws in countries for raves etc.
A bit more potent though. Used for angyna, where people think they are having heart attacks, because it causes blood vessels to dilate leading to the rush as the brain gets hypooxygenated.
Has other effects...
Poppers are the nitrited versions of these compounds.
So a bigger effect but somewhat short lived
In body builders the amylamines help blood flow so add the excerise to build muscles without depriving them of blood supply for sugar and oxygen. Guess it leads to a more vigorous work out.