Planks :)

[ny biker]

I respectfully disagree... push ups get the pecs, sure, but they are gread for the whole shoulder system, trapezeius, lats... plus if you are doing them right ( not sagging or pointing your butt in the air) it's core also.

I said primarily. Meaning it's an alternative to something like a chest press in my workout. But most of the exercises in my workout involve a combination of muscles.