I know your question is old but I believe it was answered incorrectly. I saw Michael Dorn during the years of TNG twice and he was a big guy. Not fat of course but a stocky, solid man. With age he has lost a great deal of that weight. So much so that I worried in 2012 that he would announce an illness.
Look back at pictures of Worf such as his profile pics for the show and you'll see that his arms clearly are not padded nor his chest. Perhaps his shoulders are but that would've been a sign of the times.

He wore padding as Worf to make him look more muscular.