Usually it's pretty hard for me to work hard enough to make my traps sore as they're pretty developed. BUT I tried something new last night. I did some heavy(for me) shrugging first (365x8 for the last set) Then grabbed 2 70lb dbs and layed down straddling an incline bench at around a 45 degree angle. Let the dbs hang down and then just shrug. For the first set I thought it was crap, but during the second I would hold the contraction for 3-4 seconds and by the third set I have serious lactic acid built up.