Morgan415864, you need the meshes and a skintone linked to the athletic bodyshape (or slimBB whichever shape you choose) and yes they are a custom skintone. If you want him to have this shape while showering, you must be sure to have a "showerproof" athletic skintone which you can find
here .
You will also need clothes linked to the athletic bodyshape meshes which you can find
here and
here . Many of our talented creators (like Wirelessguy and Innocent for example) have clothing to match the bodyshapes. Just browse around their sections of the forum as well as others.
If you dress him in maxis clothes he will then be in the maxis bodyshape. I love the slim bodybuilder shape, it's my favorite! :happy8: Good luck and I hope this gets you started.