If they are squating or deadlifting 2-3 times their bodyweight they will have to be pretty strong just to hold the weight. Doing lifts that activate most of the body also facilitate better growth squats and deadlifts are some of these types of movements (anyone who's done a squat workout to exhaustion knows it blows you out), doing an olympic style lift or a clean, jerk, and press movement is as close to a single total body exercies that you can get. It is possible to get big arms without specificaly working the arms (diet is a big factor). Big is reletive, compared to some pro bodybuilders these guys will be pencil necked girly men, (in best Arnold voice) but compared to us roadies they are huge.