Look at your bone structure. If you have thick joints and can easily gain weight, ENDO. If you have small joints that make your muscles look bigger but you have to fight for every once, u are an ECTO. If your in between and muscular and lean, u are a MESO. That is a short explanation of it. If you have a combination of these qualities (like most have) then u can take it from there. I am an Endo-Meso, but lean more towards the Endo side