Prolly the collar... and here's why: Look at how the pectoral muscles behave... they move in more direct proportion to their respective collar than the chest itself. Standing in front of a mirror bare-chested, you can see that your left nipple and breast/pec moves in dynamic concert with the left collarbone/shoulder joint... now try and make it move via the chest, aside from the not-so-dynamic in/out of breathing. You can make 'em move through the lateral or forward movement of the rib cage, but twisting the chest doesn't produce near as much range of motion as moving the collar does. Just my humble opinion :) /P