I don't know what it is about GS upperbody, but everytime I revisit these workouts I'm amazed at how tough they are! Granted, I heavy up on most everything but they are still killer , most specifically biceps. My forearms are so full by the end of the sequence I can barely get through. Anybody else experience this with GS? I've done STS many times over and am currently doing Xtrain, but nothing burns like GS for some reason.